CONTENTS

SCIENTIFIC AND TECHNICAL

Paton B.E., Ishchenko A.Ya. and Ustinov A.I. Application ofnanotechnology of permanent joining of advancedlight-weight metallic materials for aerospace engineering ............... 2

Tsybulkin G.A. Stabilisation of electrode melting rate inrobotic arc welding ....................................................................... 9

Kunkin D.D. System for TIG welding process control oflow-thickness steels ..................................................................... 12

Khokhlova Yu.A., Chajka A.A. and Fedorchuk V.E.Mechanism of the effect of scandium on structure andmechanical properties of HAZ of the arc welded joints onaluminium alloy V96 ..................................................................... 14

INDUSTRIAL

Khaskin V.Yu. Laser-assisted hardening and coatingprocesses (Review) ...................................................................... 18

Kovalchuk V.S. Determination of cyclic fatigue life ofmaterials and welded joints at polyfrequency loading .................... 25

Krivchikov S.Yu. Improvement of tribotechnicalcharacteristics of hardfaced cast iron automobilecrankshafts .................................................................................. 31

BRIEF INFORMATION

Pismenny A.S., Shvets V.I., Kuchuk-Yatsenko V.S. andKislitsyn V.M. On issue of brazing metals using powderbraze alloys of different dispersity ................................................ 34

Theses for a scientific degree ...................................................... 36

NEWS

Technical workshop of welding specialists in Simferopol ............... 39

Conference «Brazing-2008» in Toliatti ........................................... 41

Developed at PWI ................................................................... 8, 42

Index of articles for TPWJ’2008, Nos. 1--12 ................................... 43

List of authors .............................................................................. 47

© PWI, International Association «Welding», 2008

English translation of the monthly «Avtomaticheskaya Svarka» (Automatic Welding) journal published in Russian since 1948

International Scientific-Technical and Production Journal

Founders: E.O. Paton Electric Welding Institute of the NAS of Ukraine Publisher: International Association «Welding» International Association «Welding»

Editor-in-Chief B.E.Paton

Editorial board:Yu.S.Borisov I.A.Ryabtsev

A.Ya.Ishchenko V.F.KhorunovB.V.Khitrovskaya I.V.Krivtsun

S.I.Kuchuk-YatsenkoYu.N.Lankin L.M.Lobanov

V.N.Lipodaev A.A.MazurV.I.Makhnenko I.K.PokhodnyaO.K.Nazarenko K.A.Yushchenko

A.T.Zelnichenko

International editorial council:N.P.Alyoshin (Russia)

U.Diltey (Germany)Guan Qiao (China)

D. von Hofe (Germany)V.I.Lysak (Russia)

N.I.Nikiforov (Russia)B.E.Paton (Ukraine)

Ya.Pilarczyk (Poland)P.Seyffarth (Germany)

G.A.Turichin (Russia)Zhang Yanmin (China)

A.S.Zubchenko (Russia)

Promotion group:V.N.Lipodaev, V.I.Lokteva

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All rights reserved.This publication and each of the articles

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December2008# 12

APPLICATION OF NANOTECHNOLOGY OF PERMANENTJOINING OF ADVANCED LIGHT-WEIGHT METALLIC

MATERIALS FOR AEROSPACE ENGINEERING

B.E. PATON, A.Ya. ISHCHENKO and A.I. USTINOVE.O. Paton Electric Welding Institute, NASU, Kiev, Ukraine

The paper deals with the possibility of making solid-phase joints of advanced structural quasi-crystalline and intermetallicalloys, aluminium composites and nanomaterials by diffusion and friction stir welding using nanostructured fillers. It isshown that these welding processes allow producing permanent joints of difficult-to-weld materials applied in fabricationof aerospace products, parts of gas turbine engines, electrical engineering and heat exchanger units, in repair andrestoration operations.

K e y w o r d s : aluminium alloys, aluminium composites, quasi-crystalline alloys, intermetallic materials, weldability, perma-nent joint, solid-phase joint, self-propagating high-temperaturesynthesis, diffusion welding, friction stir welding, nanostruc-ture, mechanical properties, welded structures, aerospace engi-neering

At the start of the XXI century it has become necessaryto cardinally improve the scientific-technical level ofeconomics all over the world. Solving this problemrequires conducting extensive research, as well as massintroduction of advanced technologies into produc-tion. According to the predictions of many competentorganizations, development of nanomaterials andnanotechnologies is a high priority. These are exactlythe materials and technologies which, alongside oth-ers, will promote an essential improvement of produc-tive efficiency in such spheres as mechanical engineer-ing, power engineering, construction, agriculture,medicine, etc.

By now new light aluminium alloys and compositematerials with extraordinary properties due to the qua-sicrystalline or nanodispersed structure of semi-fin-ished products have already been developed for fab-rication of aerospace engineering structures [1, 2]. Itshould be noted that with regular welding processes,metallic materials are heated to a temperature, whichresults in their melting or activation of diffusion proc-esses in the joint zone. In the case of application ofnanostructured composite materials, alloys based onintermetallics or other high alloys heating up to a hightemperature leads to irreversible structural transfor-mations [3] and degradation of the initial physico-me-chanical properties of the material [4]. In this con-nection, an urgent problem is lowering of temperatureand reduction of the duration of weld formation proc-ess in order to preserve the initial structure and levelof material properties in the joint zone. Among thediverse currently available welding processes those ofsolid-phase joining, i.e. without metal melting, shouldbe more widely accepted. These include, primarily,diffusion welding and friction stir welding [5].

The idea of solving such a problem, on the whole,is based on that the temperature of the solid-phasejoining process can be reduced, if rapidly crystallized-amorphized homogeneous strips [6] or composite thin-film materials with a nanolayered structure [1] areused as welding fillers. In such materials the non-equi-librium state of the fine structure leads to an essentiallowering of temperature, at which the diffusion proc-esses are running intensively. Formation of soundjoints is promoted by application of multilayerednanostructured films, consisting of metals enteringinto an exothermal reaction of intermetallic synthesis.

Let us consider a number of specific examples ofnanolayered filler application and the results of PWIwork in this field for light materials for aerospaceapplications.

For solid-phase joining of high-temperature mate-rials, including intermetallic alloys, thin nanostruc-tured foils from multilayered compositions of variousmetal elements of Ti/Al, Ni/Al, Cu/Al, etc. havebeen developed and are used as welding fillers. Theirmanufacture is based on the process of layer-by-layerconsolidation of elements from the vapour phase, usingelectron beam vacuum technology (Figure 1). Thedeposition technology enables adjustment of the proc-ess of layered structure formation in a broad range ofthicknesses of individual layers ---- from severalnanometers up to tens of micrometers (Figure 2, a).

At heating the nanostructured foils are prone todevelopment of the reaction of self-propagating high-temperature synthesis (SPHTS) of intermetallic com-pounds, which runs very quickly and is characterizedby exothermal effect. The necessary condition for join-ing materials without melting due to activation ofdiffusion processes in the solid state is a stable runningof SPHTS reaction. As shown by experience, this re-quires application of multilayer foils of more than30 µm thickness (Figure 2, b).

Diffusion bonding of microdispersed high-strength aluminium composite of AMg5 + 27 % Al2O3

system with application of interlayers from nano-structured multilayer foils turned out to be more ef-fective than arc welding [4]. The metal matrix of this

© B.E. PATON, A.Ya. ISHCHENKO and A.I. USTINOV, 2008

2 12/2008

material contains a large quantity of the strengtheningphase in the form of insoluble particles of aluminiumoxide, and, therefore, it is difficult to treat and toweld. Figure 3, a shows the structure of the compositein the initial condition, differing by a set of valuableproperties, namely high specific modulus of elasticity,room and higher temperature strength, wear resis-tance, low coefficient of linear expansion. This mate-rial is widely applied in products for aerospace andtransportation engineering.

Performance of fusion welding of the consideredaluminium composite is difficult in view of the in-creased viscosity of weld pool metal and susceptibilityof reinforcing Al2O3 particles to agglomeration. Thestrengthening particle conglomerates forming in thewelds lower the strength and corrosion resistance ofthe produced joints [7]. In diffusion welding at lowertemperatures segregation of the strengthening phaseparticles and chemical reactions between the compos-ite material components are practically absent. In thisconnection the solid-phase process of joining a mi-crodispersed composite based on aluminium reinforcedby Al2O3 ceramic particles is preferable [8]. Weldstrength in regular diffusion welding using one-layerplastic aluminium foil does not exceed 50--60 % ofbase material strength (Figure 3, b).

For activisation of the diffusion welding processand improvement of weld strength, interlayers (fill-ers) from multilayered nanostructured foils of twotypes, namely Ti/Al and Cu/Al were used (Fi-gure 4). The first of them was 60 to 150 µm thick at 50to 150 nm thickness of the nickel and aluminium nano-layers and corresponded to the stoichiometric composi-tion of Ni3Al intermetallic, and the second, having ap-proximately the same thickness, corresponded to thecomposition of Al + 33 % Cu eutectic [9].

It is established that replacement of regular alu-minium interlayer (basic variant) by nanolayered con-densate foil allows lowering the composite weldingtemperature by 80--100 °C, providing sound formationof the permanent joint at a lower welding pressure,which does not cause any noticeable macroplastic de-formation in the welded materials. When Cu/Al foilis used, a complete dissolution of the filler in the jointzone is also noted (Figure 3, c, d). Weld metalstrength increases up to the base metal level (Fi-gure 5). Coefficient of joint strength is equal to 0.87to 0.90.

Diffusion welding of intermetallic alloy based onγ-TiAl titanium aluminide using interlayers from mul-tilayered nanostructured Ti/Al, Ni/Al, Ti/Ni foilsis a practically real and effective method of joiningadvanced high-temperature materials [10--12]. As anexample, let us consider Ti--48Al--2Nb--2Mn (at.%)intermetallic alloy operating at 700--1100 °C, i.e. muchhigher than the operating temperature of currentlyavailable titanium superalloys (T ≤ 600 °C) [13]. Thiswill enable application of the above alloy for gas tur-bine engines, flying vehicle skin, parts of load-carry-ing structures of aerospace engineering products, etc.

Alloys based on γ-TiAl are light (density of 3.8--4.0 g/cm3) and resistant to oxidation at up to 900--1000 °C temperature. Their modulus of elasticity atroom temperature is equal to 160--175 GPa, and at900--1000 °C it decreases to 150 GPa. Industrial ap-plication of the above material is restrained by its lowductility at standard temperature (δ = 0.1--0.5 %).Semi-finished product treatability is made difficult bythe high deformation resistance of the material.

Figure 1. Schematic of the process of electron beam deposition ofmultilayered condensates: 1 ---- electron beam sources (guns) forheating; 2 ---- substrate; 3 ---- separating impermeable screen; 4 ----crucibles for ingot evaporation; 5 ---- electron beam guns for evapo-ration

Figure 2. Microstructure of a multilayered nanostructured Ni/Alcondensate, produced by electron beam vapour phase deposition invacuum, in the initial condition (a) and after SPHTS reaction atthe temperature of 500 °C (b)

12/2008 3

In the initial condition Ti--48Al--2Nb--2Mn (at.%)alloy develops a fully lamellar structure, which is

presented by practically equiaxed grains of 60--120 µmsize with plates (lamels) of γ- and α-phase with dif-ferent orientation within each grain. Dispersed inclu-sions with an increased niobium content uniformlydistributed through the matrix volume, form againstthe background of the lamellar structure. Alloy mi-crohardness is equal to 3000--4000 MPa.

Permanent joints of components from this materialwere made by diffusion welding in vacuum using mul-tilayered Ti/Al, Ti/Ni, Ni/Al foils of the total thick-ness from 10 up to 20 µm by layer-by-layer depositionfrom the vapour phase of individual nanosized layersof the respective components using electron beam tech-

Figure 4. X-ray diffraction spectra of foils of γ-TiAl intermetallics(a) and nanodispersed eutectic composition Al + 33 % Cu (b):l ---- Al; m ---- Al2Cu; I ---- radiation intensity; θ ---- angle ofdiffraction

Figure 3. Microstructure of base metal ---- AMg5 + 27 % Al2O3 composite (a) and its permanent joints produced by diffusion weldingusing single-layer aluminium interlayer (b), as well as multilayered nanostructured foil corresponding to intermetallic composition ofNi3Al (c) or eutectic composition of Al + 33 % Cu (d) (a ---- ×200; b--d ---- ×400)

Figure 5. Tensile strength σt of base metal (1) and joints of AMg5 +27 % Al2O3 aluminuim composite produced by diffusion weldingusing nanolayered foil of Al--Cu system (2) and single-layer alu-minium strip (3)

4 12/2008

nology. Welding was performed in U-394 unit de-signed for diffusion welding and fitted with circularelectron beam heaters of blanks. Equivalent jointswith a favourable structure were obtained using nano-layered Ti/Al foil of the total thickness of 20 µm inthe following welding mode: welding temperatureTw = 1200 °C; welding time τ = 20 min; pressure P == 45 MPa.

Metallographic analysis of the structure revealeda continuous uniform weld 15--18 µm wide (Figure 6,a), the metal of which corresponds to the main γ-TiAlintermetallic phase as to its composition (Figure 7).A fine-grain zone, formation of which is due to therecrystallization process, is revealed near the weld at5--10 µm distance. Microhardness values of 3500--4200 MPa in the joint zone are close to analogous indexof the base metal (3000--4000 MPa) in the initial con-dition, which is indicative of equivalent strength of theweld metal compared to base material (Figure 6, b).

When foils of Ni/Al and Ti/Ni systems are used,the joint zone develops structural components withmicrohardness 2--3 times higher than that of the basematerial ---- Ti--48Al--2Nb--2Mn alloy (at.%). Increaseof microhardness (Figure 8) can promote lowering ofjoint ductility.

The above confirms that vacuum diffusion weldingusing nanolayered Ti/Al foils allows producing soundhomogeneous equivalent joints of Ti--48Al--2Nb--2Mnintermetallic alloy.

Friction stir welding of quasi-crystalline high-temperature alloy of Al--Fe--Cr--Ti system withoutfillers is an example of producing an original alloywith quasi-crystalline strengthening and a new frictionstir welding process with layer-by-layer stirring of theweld metal (Figure 9, a). The weld metal structure andits mechanical properties are improved owing to inten-sive plastic deformation under the conditions of three-dimensional compression in friction stir welding.

High-temperature aluminium alloy based on Al--Fe--Cr--Ti system was in the form of extruded semi-finished products with a nanostructured matrix,formed at rapid solidification of the initial materialin the form of finest granules (actually, powders) withparticles of less than 100 µm size. Alloy strengtheningis due to presence in its composition of nanosized quasi-crystalline intermetallic particles [14]. Intermetallicphases present in the above alloy composition, containtransition refractory elements, which strengthen thesolid solution (aluminium matrix) and reduce the dif-fusion rate in it (Figures 10 and 11). Extruded semi-finished products are characterized by the followingmechanical properties: σ0.2 = 485 MPa, σt = 542 MPa,δ = 7 % (at room temperature), σ0.2 = 283 MPa, σt == 297 MPa, δ = 3.5 % (at 300 °C). The alloy belongsto a new material class designed for engineering ap-plications in the case, when it is necessary to reducethe weight of a structure operating at increased (up

Figure 6. Microstructure of the joint zone of an alloy based on γ-TiAl intermetallics (Ti--48Al--2Nb--2Mn) produced by diffusion welding(temperature of 1200 °C) using nanolayered foil corresponding to γ-TiAl intermetallic compound in its composition (a ---- ×200; b ----×300): t ---- diamond indentor imprints

Figure 7. Nature of distribution of manganese, aluminium, niobiumand titanium in the joint zone of an alloy based on γ-TiAl inter-metallics (Ti--48Al--2Nb--2Mn) produced by diffusion welding at1200 °C using nanolayered foil corresponding in its composition toγ-TiAl intermetallic compound: l ---- distance from weld axis

Figure 8. Nature of distribution of HV microhardness in the weldzone at diffusion welding of Ti--48Al--2Nb--2Mn intermetallic alloywith application of interlayers from nanolayered foils of differentsystems: 1 ---- Ni--Al; 2 ---- Ti--Ni; 3 ---- Ti--Al

12/2008 5

to 300--400 °C) temperature and ensure sufficientlyhigh specific strength. These requirements are urgentfor many types of vehicle structures, for instance inaircraft and engine construction.

The results of investigation of friction stir weldingand of the produced joint properties showed that theweld metal forms a more dispersed and uniform grainstructure than in the base metal with the size of matrixd ≤ 300 nm and quasi-crystal particles d ≤ 100 nm, ul-timate strength of the joints being 370 MPa.

Scanning electron beam microscopy revealed thespecific nature of the structure of base metal andwelds, which is formed under the conditions of inten-sive plastic deformation (Figure 12, a, b).

Friction stir welding of nanodispersed aluminiumcomposite Al + Al2O3 without fillers is another exam-ple of acceptance of new developments by industry.Electron beam vapour-phase technology enablesmanufacturing compact billets of nanostructured ma-terial in the form of sheets [7, 15], and well as othershapes, typical for three-dimensional structures (cy-lindrical, conical, semi-spherical). Friction weldingwith multilayer stirring ensures their joining underthe conditions, when base material properties are pre-served to a great extent.

Experimental verification of this idea was startedwith welding of samples of sheet aluminium compos-ite, reinforced by insoluble particles of Al2O3 oxide.Such a material operates at a higher temperature thando regular aluminium alloys.

Composite structure is characterized by columnarcrystals directed normal to the flat sample surface(Figure 12, c, d). Oxide inclusions of the size of 10--50 nm, are uniformly distributed, particle spacing be-ing 60--100 nm. Composite hardness is HRB 99--100 MPa, its strength being σt = 340 MPa.

Plates of nanodispersed Al + 7 % Al2O3 compositewere joined by friction stir welding at the speed of14 m/h, working tool rotation frequency being1420 rpm. Figure 9, b gives the appearance of theproduced weld. Metallographic studies showed thatduring welding transformation of columnar crystal-lites into equiaxed grains occurs in the joint zone,their size being reduced 3--5 times (Figure 12, c, d).Base metal hardness is equal to 680--700 MPa, thatof weld metal being 780--900 MPa. Friction stir weld-ing provides equivalent joints, owing to improved ho-mogeneity and dispersed state of the structural con-stituents.

Thus, considered are the examples of joining dif-ficult-to-weld regular and nanodispersed materials us-ing nanostructured fillers in the form of strips, foilsand films made by the method of layer-by-layer con-solidation of metals from the vapour phase using elec-tron beam technology. Thin foils from activated mul-tilayered nanostructured compositions of Ti/Al,Ni/Al, Ni/Ti and other metals prone to SPHTS re-action of intermetallic compounds, have been devel-

Figure 9. Schematic of friction stir welding of nanodispersed alu-minium composite Al + 7 % Al2O3 (a) and weld appearance (b):1 ---- rotating working tool; 2 ---- direction of tool displacement inwelding; 3 ---- weld

Figure 10. Quasicrystalline particles of intermetallic phase precipitating in rapidly solidified fine granules of Al--3Fe--3Cr alloy: a, b ----images obtained by the method of scanning electron microscopy in back-scattered electrons, a, and characteristic X-ray radiation

6 12/2008

oped for their practical application in welding variousmetallic materials.

Advanced technologies of joining different kindsof nanostructured materials are realized using diffu-sion welding or friction stir welding. Use of new fillersand welding technologies enables successfully joiningadvanced structural materials with special propertiessuch as those of intermetallics of Ni--Al and Ti--Alsystems, high-strength quasicrystalline aluminium al-loys, nanodispersed or nanolayered light compositematerials.

Diffusion welding allows joining predominantlycompact small-sized products and components for air-

craft and rocket engines, and is also applied in manu-facturing of equipment for nuclear engineering, elec-trical and electronic engineering.

Friction stir welding is used in manufacture of prod-ucts of large dimensions and diverse shape, for instance,flat panels and shells, panels and volume frames, tanksfor liquid fuel and cases of various machines. Butt, filletor overlap welds (straight and curvilinear, extended,intermittent and spot) are made [5].

The authors are expressing their sincere gratitudefor active participation in performance of this re-search to Yu.V. Milman, Corresp. Member of NASU,

Figure 12. Microstructure of base metal (a, c) and weld metal (b, d) made by friction stir welding: a, b ---- extruded strip fromquasicrystalline alloy of Al--Cr--Fe system; c, d ---- nanodispersed aluminium composite Al + 7 % Al2O3 (×400)

Figure 11. X-ray diffraction of fine granules of Al--3Fe--3Cr (a) and Al--2.5Fe--2.5Cr--0.5Ti--0.5Zr (at.%) alloys (b): r ---- quasicrystallinephase

12/2008 7

A.I. Sirko and L.A. Olikhovsky, Cand. of Sci.(Eng.), G.K. Kharchenko, Dr. of Sci. (Eng.), Yu.V.Falchenko and A.G. Poklyatsky, Cand. of Sci.(Eng.), V.E. Fedorchuk, A.N. Muravejnik, Yu.A.Khokhlova, A.A. Chajka, Eng.

1. Movchan, B.A. (2004) Electron beam technology of vapor phaseevaporation and deposition of inorganic materials with amor-phous, nano- and microdimensional structure. Nanosistemy,Nanomaterialy, Nanotekhnologii, 2(4), 1103--1126.

2. Inoue, A., Kimura, H. (2000) High-strength aluminum al-loys containing nanoquasicrystalline particles. Mater. Sci.and Eng. A, 286(1), 1--10.

3. Ustinov, F.I., Olikhovskaya, L.A., Polishchuk, S.S. (2006)Metastable nanostructural states in coatings of Ni--Al systemmade by vapor phase deposition. Metallofizika i Nov.Tekhnologii, 6, 32--37.

4. Ryabov, V.R., Muravejnik, A.N., Bondarev, A.A. et al.(1999) Study of structure of welded joints of dispersion-strengthened aluminium alloy. Tekhnologiya Lyog. Splavov,1/2, 139--144.

5. Ishchenko, A.Ya., Podielnikov, S.V., Poklyatsky, A.G.(2007) Friction stir welding of aluminium alloys (Review).The Paton Welding J., 11, 25--30.

6. Milman, Yu.V. (2005) Mechanical behavior of nanostruc-tured aluminium alloys containing quasicrystalline phase.Mater. Sci. Forum, 482, 77--82.

7. Ishchenko, A.Ya., Tretyak, N.G., Lozovskaya, A.V. et al.(1993) Weldability of nanodispersed material of Al--Al2O3

system produced by vapor phase condensation. Avtomatich.Svarka, 5, 16--19.

8. Ishchenko, A.Ya., Kharchenko, G.K., Falchenko, Yu.V. etal. (2006) Vacuum solid-phase joint of dispersion-strengthe-ned composite materials. Nanosistemy, Nanomaterialy, Na-notekhnologii, 4(3), 747--756.

9. Ishchenko, A.Ya., Falchenko, Yu.V., Ustinov, A.I. et al.(2007) Diffusion welding of finely-dispersed AMg5/27 %Al2O3 composite with application of nanolayered Ni/Al foil.The Paton Welding J., 7, 2--5.

10. Povarova, K.B., Bannykh, O.A. (1999) Principles of produ-cing of intermetallic-base structural alloys. Part 1. Materia-lovedenie, 2, 27--33; Part 2. Ibid., 3, 29--37.

11. Yushtin, A.N., Zamkov, V.N., Sabokar, V.K. et al. (2001)Pressure welding of intermetallic alloy γ-TiAl. The PatonWelding J., 1, 33--37.

12. Duarte, L.I., Ramus, A.S., Vieira, M.F. et al. (2006) Solid-state diffusion bonding of gamma-TiAl alloys using Ti/Althin films as interlayers. Intermetallics, 14, 1151--1156.

13. Ustinov, A.I., Falchenko, Yu.V., Ishchenko, A.Ya. et al.(2008) Diffusion welding of gamma-TiAl based alloysthrough nanolayered foil of Ti/Al system. Ibid., 16, 1043--1045.

14. Milman, Yu.V., Sirko, A.I., Iefimov, M.O. et al. (2006)High strength aluminium alloys reinforced by nanosize qua-sicrystalline particles for elevated temperature application.High Temperature Materials and Processes, 25(12), 19--29.

15. Poklyatsky, A.G., Ishchenko, A.Ya., Yavorskaya, M.R.(2007) Strength of joints on sheet aluminium alloys pro-duced by friction stir welding. The Paton Welding J., 9,42--45.

8 12/2008

STABILISATION OF ELECTRODE MELTING RATEIN ROBOTIC ARC WELDING

G.A. TSYBULKINE.O. Paton Electric Welding Institute, NASU, Kiev, Ukraine

One of the approaches to reduction of external disturbances affecting the electrode melting rate in robotic arc weldingis considered. The procedure providing synthesis of the compensating circuit, based on the invariance principle, isdescribed. Computer simulation results are presented.

K e y w o r d s : arc welding, robotics, stabilisation of condi-tions, compensation of disturbances, structural synthesis

It is a well known fact that the key destabilisingfactors in automatic metal arc welding are unpre-dictable changes in: a) voltage at output terminals ofthe welding current source; b) electrode wire feedspeed; and c) distance between the tip of the current-conducting nozzle and free surface of the weld pool.The issues of decreasing the effect of these factors onquality of the welded joints are described in numerousstudies, which suggest a number of interesting ap-proaches [1--8]. The idea they share consists in stabi-lisation of the arc welding process parameters in oneway or another. Study [7] puts forward cross-connec-tions between the welding current source voltage andelectrode wire feed speed to provide partial stabilisa-tion of the above parameters. Study [8] proposes usingthe absorption principle to achieve a more substantialdecrease in the effect of the destabilising factors. Thisprinciple is based on compensation of external distur-bances through adding a specially synthesised com-pensation connection to a structural scheme of thewelding circuit.

Meanwhile, robotic arc welding is characterised bythe feasibility of compensating for the harmful effect ofthe destabilising factors with no structural changes inthe welding circuit proper. In particular, the fluctuationsof voltage that form at the output terminals of the weld-ing current source can be compensated for in some casesby means of corrective control of distance between thetip of the torch located in a gripping device of the in-dustrial robot and free surface of the weld pool as func-tion of the above voltage.

The present study considers the problem of syn-thesis of structure of the compensating circuit andalgorithm of the corrective control of position of thewelding torch using a manipulation robot on the basisof current information on a change in voltage of thewelding current source.

Consider a mathematical model of the welding cir-cuit in the form of a structural scheme (Figure 1) byusing the following designations: ve ---- metal electrodefeed speed with respect to the torch nozzle; vm ----electrode melting rate; ∆v = ve -- vm; H ---- distancebetween the tip of the current-conducting nozzle and

free surface of the weld pool; h ---- electrode extension;l ---- length of the arc gap; E ≡ dua/dl ---- intensityof the electric field in the arc column; ua ---- arc volt-age; u0 ---- sum of the near-electrode voltage drops;us ---- voltage at the output terminals of the weldingcurrent source; ∆u = us -- ua -- u0; M ≡ dvm/di ----steepness of the electrode melting characteristic atrated values irated of the welding current and electrodeextension hrated; R* = R + Sa -- Ss, where R is the totalresistance of lead wires, electrode extension and slid-ing contact in the torch nozzle; Sa ≡ dua/di; Ss ≡≡ dus/di ---- steepness of volt-ampere characteristicsof the arc and welding current source at rated valueirated of the current; L ---- inductance of the weldingcircuit; and D = d/dt ---- operator of differentiation.

According to the structural scheme shown in Fi-gure 1, write down equation of the electrode meltingrate in the operator form:

vm = W ve -- DH +

1E

Dus

, (1)

where

W = W(D) = 1

TeTsD2 + TsD + 1

; Te = LR∗

; Ts = R∗

EM .

It can be seen from expression (1) and Figure 1that the external disturbances affecting speed ve, dis-tance H and voltage us may lead to deviation of elec-trode melting rate vm from its rated values, which,naturally, may impact quality of the welded joint. Inrobotic arc welding, the fluctuations of electrode wirefeed speed ve are insignificant, as a rule. Unpredictablechanges in voltage us at the output terminals of thewelding current source are most often related to loadinstability in the industrial mains. In this connection,consider a case where ve = const, and disturbance ofthe rated arc welding conditions is caused by a short-time change in voltage us.

Figure 1. Structural scheme of welding circuit (for designationssee the text)© G.A. TSYBULKIN, 2008

12/2008 9

It can be easily seen from analysis of expression(1) that to ensure independence of electrode meltingrate vm upon fluctuations of us it is enough to meetthe following condition:

1E

Dus -- DH = 0, (2)

which, according to the theory of automatic control[9--12], can be called the invariance condition withrespect to disturbances. It is known that the mainproblem of the invariance theory is to find such struc-tural solutions, at which arbitrary-type external dis-turbances could have a minimal negative effect onbehaviour of a controlled process. The most favourablesituation for solving this problem is when it is possibleto directly measure the external disturbances, al-though the laws of their changes with time may notbe known beforehand. In our case, any deviations inξ(t) = us(t) -- us rated, where us rated is the rated valueof voltage of the welding current source, can be readilymeasured. Therefore, to meet condition (2) it is suf-

ficient to ensure the automatic control of distance Hin accordance with the algorithm:

H(t) = Hrated + ∆H(t), (3)

where

∆H(t) = 1E

ξ(t). (4)

It is clear that algorithms (3) and (4) in the aboveform are physically unrealisable, as the actuators,whose task is to provide spatial movement of the weld-ing torch, have some lag effect. Therefore, let us mod-ify expression (4) as follows by using the mathemati-cal model of an inertial link:

∆H(t) = 1

E(TD + 1) ξ(t), (5)

where T is the time constant of the actuators.Structure of the compensating circuit based on al-

gorithms (3 and (5) is shown in Figure 2. It can beseen from this Figure that the requirement to structureof the circuit, formulated as the two-channel principle[10], is met: disturbance ξ(t) is transmitted via twochannels, and the total effect at exit of these channelsis σ = ∆u -- ∆u* = ξTD/(TD + 1), where ∆u* = ∆u atξ = 0 is much lower than ξ(t) at low T. Hence, elec-trode melting rate vm becomes invariant to some extentwith respect to disturbing effect ξ(t).

Characteristic peculiarity of this method for com-pensation of disturbances is that the compensationdevice (CD) (Figure 2), which in fact is an externaldevice with respect to the welding circuit, does notintroduce any changes into its structure, in contrastto other known methods. The ξ(t) signal read outfrom the sensor of voltage us arrives, after preliminaryprocessing, directly to the control device of the ma-nipulation robot, which, according to algorithm (5),moves the welding torch to calculated distance ∆H(t),

Figure 2. Structural scheme of compensation circuit

Figure 3. Results of computer simulation (see explanations in the text)

10 12/2008

thus decreasing the effect of disturbance ξ(t) on elec-trode melting rate vm(t).

Computer simulation of dynamics of the processesoccurring in the circuit during arc welding was carriedout to experimentally check the efficiency of the sug-gested approach to stabilisation of electrode meltingrate vm. Numerical values of parameters of the circuitand arc welding process were as follows: L = 7⋅10--4 H;R = 0.015 Ohm; Sa = 0.005 V/A; Ss = --0.02 V/A;us = 24 V; u0 = 12 V; ve = 50 mm/s; H = 17 mm;E = 2 V/mm; and M = 0.38 mm/(A⋅s).

Variation in voltage us at the output terminals ofthe welding current source was regarded as an externaldisturbance, the law of changes of which was set bythe following relationship:

us(t) = 24 -- ξ(t), (6)

where

ξ(t) = 4 exp [-- n(t -- 1.5)2]. (7)

(Graphs of function (6) at n = 2 s--2 and n = 5 s--2 areshown in Figures 3, a, and 4, a, respectively.)

Results of simulation of process (1) at the distur-bances of type (7) are presented in Figures 3 and 4,which show graphs of changes of vm(t) in the weldingcurrent without CD (Figure 3, b, and Figure 4, b)and with CD (Figure 3, c, d, and Figure 4, c, d). Itcan be seen by from these graphs that at the absenceof CD (see Figure 1) disturbance (7) leads to a sub-stantial change in electrode melting rate vm(t) (Fi-gure 3, b, and Figure 4, b). Upon connecting CD (seeFigure 2), the effect of disturbance (7) on electrodemelting rate vm(t) becomes much mitigated (Figure 3,c, d, and Figure 4, c, d).

As might be expected, the extent of compensationof disturbance ξ(t) in the given scheme depends uponthe lag effect of the actuators that move the torch.

Figure 3, d shows graph vm(t) plotted for T = 0.05 s,and Figure 4, d ---- for T = 0.1 s. It can be seen fromthese graphs that the extent of compensation of dis-turbances grows with decrease in the lag effect of theactuators.

It can be well seen by comparing graphs in Figure 3,c, d, and Figure 4, c, d that the «slower» disturbancesaffect electrode melting rate vm to a lesser degree thanthe «rapid» ones. This shows that the disturbances thespeed of changes of which is lower than the speed ofattenuation of the transient processes are compensatedfor most efficiently in the welding circuit.

Therefore, as shown by the results of computer simu-lation, adding an extra connection between the weldingcurrent source and torch movement control device tothe system of robotic control of the metal arc weldingprocess can be a very efficient method for compensationof slow fluctuations in voltage of this source.

1. Paton, B.E. (1958) Some problems in the field of automaticcontrol of welding processes. Avtomatich. Svarka, 4, 3--9.

2. Paton, B.E., Lebedev, V.K. (1966) Electric equipment forarc and slag welding. Moscow: Mashinostroenie.

3. Dyurgerov, N.G., Penivshi, V.A., Sagirov, Kh.N. (1966)About stability of metal-electrode pulse-arc welding process.Svarochn. Proizvodstvo, 7, 13--14.

4. Gladkov, E.A. (1976) Automation of welding processes.Moscow: N.E. Bauman MVTU.

5. Lebedev, A.V. (1978) Efficiency of stabilisation of meanvalue of the current in semiautomatic welding. Avtomatich.Svarka, 10, 37--41.

6. (1986) Automation of welding processes. Ed. by V.K. Lebe-dev, V.P. Chernysh. Kiev: Vyshcha Shkola.

7. Paton, B.E., Shejko, P.P., Zhernosekov, A.M. et al. (2003)Stabilization of the process of consumable electrode pulse-arc welding. The Paton Welding J., 8, 2--5.

8. Tsybulkin, G.A. (2007) Compensation of external distur-bance action on consumable electrode arc welding mode.Ibid., 4, 5--8.

9. (1987) Reference book on automatic control theory. Ed. byA.A. Krasovsky. Moscow: Nauka.

10. Tsybulkin, G.A. (1979) Invariance and stability of one classof combined software systems with variable scale of programtime. In: Theory of invariance and its application. Pt 2.Kiev: Naukova Dumka.

11. Kukhtenko, A.I. (1963) Problems of invariance in automat-ion. Kiev: Gostekhizdat Ukr. SSR.

12. Tsypkin, Ya.Z. (1996) Synthesis of structure of stabilisingand invariant regulators. Doklady RAN, 347(5), 607--609.

Figure 4. Results of computer simulation (see explanations in the text)

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SYSTEM FOR TIG WELDING PROCESS CONTROLOF LOW-THICKNESS STEELS

D.D. KUNKINE.O. Paton Electric Welding Institute, NASU, Kiev, Ukraine

The version of the pulsed-arc welding mode using a low-amperage welding current source with the PWM regulation andan experimental control system with application of microprocessor devices is presented.

K e y w o r d s : TIG welding, pulsed arc, microprocessor, regu-lation using pulse-width modulation, thin-sheet metal

The TIG welding of steels up to 0.5 mm thickness iswidely used in instrument making (assembly of hous-ings and screens) and to a smaller degree in automotiveindustry in performance of repair-restoration works.Other fields of its narrowly specialized applicationare possible as well where use of standard weldinginvertors is inadvisable.

In this work the issue was solved to build a controlsystem for welding of a thin-sheet metal with the leastmaterial expenses and consumption of time. For re-ducing heat input into the metal and probability ofburn-through the direct current welding with low-and medium-frequency modulation (pulsed-arc weld-ing) was used. Regulation of the current duration inthe pulse and in the pause, and frequency of repetitionof the pulses was performed using the ATMEGA8515microcontroller (of the Atmel company). In the modu-lated current welding by means of changing of mini-mum four regulated parameters (pulse duration, fre-quency of its repetition, current amplitude in thepulse, and the base current level) it is possible toestablish optimal conditions for welding. On the ex-perimental specimen it is convenient to use a unifiedprogrammable module for processing commands of awelder and controlling regulated parameters with in-dication of the set values, which allows adopting thecontrol system according to different requirements andtasks [1, 2].

As object of the control a low-amperage weldingcurrent source was used, developed at the sub-unit ofthe E.O. Paton EWI ---- State Scientific-EngineeringCenter of Welding and Control in the Field of NuclearPower Engineering of Ukraine. This source of currentis a component of the simulator for a welder (Figure 1)and represents a pulse-width down-converter with thecontrol system.

Stabilization of the welding current using the feed-back signals, received from the current sensor 3, isperformed according to the law of the pulse-widthmodulation, implemented by the TL 494 microcircuit1. For matching output signal of the microcircuit 1and the power transistor the IR 2110 microcircuit-driver 2 is used. The current feedback signal from the

sensor is compared with the reference voltage level,due to which signal of the error is produced that iscompared with the saw-tooth signal. As a result thepower transistor control pulses are formed with a fre-quency which is determined by parameters of the ex-ternal time-setting circuit of the saw-tooth voltagegenerator (STVG), in our case it equaled 20 kHz.Duration of open state of the transistor is directlyproportional to difference between the error signaland the reference voltage. Due to stored energy of thechoke L1 the current pulses transform into continuouscurrent, mean value of which is maintained at constantlevel with a certain accuracy.

Conditions of the pulsed-arc welding were imple-mented as follows. The microcontroller ensures gen-eration of the signal, time diagram of which is pre-sented in Figure 2. In the program adjustment by theoperator of the pulse cycle duration and the pausedirectly in the course of the device operation with50 µs discreteness is foreseen. A welder using the keys«higher»/«lower» (or digital potentiometers) setsvalues of the coefficients which correspond to the du-ration of the pulse Tpulse and the pause Tpause (from 0to 225) which are multiplied by 50 µs. Frequency ofthe output pulses may be determined using the formula

fout = 1/(TpulseT + Tpause + dt) [Hz],

where dt is the «dead time» duration (duration of thecontrol resistor switched-off state before each newcycle) equal to 10 µs; T is the program time unit equalto 50 µs.

Pulsed signal of the assigned frequency is fed fromthe microcontroller 6 to the optron key 5. The keyshunts the reference voltage attenuator resistor 4, thecompared level of the reference voltage sharply in-creases, due to which open state of the power transistorincreases, and value of the welding current approachesthe maximum one. Ratio between maximum and mini-mum values of the current may be changed by theoperator. Frequency of the jump-like change of thereference signal is determined by frequency of themicrocontroller pulse generation and is selected bythe operator as combination of the pulse and the pauseduration. Its selected values are imaged on the seven-segment indicator of the dynamic indication unit 7.

Maximum frequency of the output signal, whichis the modulation frequency, equals fout =© D.D. KUNKIN, 2008

12 12/2008

= 1⋅106/(1⋅50 + 1⋅50 + 10) = 9.1 kHz. It should benoted that such fout value of the welding current en-ables increase of the arcing stability but does not effectits energy parameters because of inertia of the heatprocesses. Minimum value of the output signal fre-quency equals 39.2 Hz.

In the course of carrying out the experiments ac-ceptable stability of the arcing without burns-throughwas achieved at the following parameters of the proc-ess: steel ---- the galvanized ST0 sheet of 0.55 mmthickness; duration of the pulse and the pause was4.9 ms (Tpause = Tpulse = 98) which corresponds to thefrequency of pulses fout = 100 Hz at relative pulseduration of 50 %. Range of the jump-like change ofthe reference voltage constitutes 50 % of the basevalue. So, for maximum current (10 A) the range ofits pulsations equals approximately 5 A, whereby volt-age values in the arc gap vary from 16 to 20 V. Os-cillogram of the modulated welding current is pre-sented in Figure 3.

Proceeding from results of the carried out workone may draw the following conclusions.

Described method of building the control systemfor pulsed-arc welding of a thin-sheet metal is eco-nomical and at the same time sufficiently flexible so-lution for different fields of application. Shortcomingof such method for achieving welding current pulsa-tions consists in periodic change of amplification fac-tor of the error signal amplifier due to which accuracyof the current stabilization in the pulse is worse thanin the pause. Adjustment of the pulse and the pausecurrent levels does not occur independently, it is per-formed simultaneously, due to which the operatorneeds long time to perform adjustment of the necessarycurrent values. The advantage consists in convenienceof digital independent regulation of the pause pulseduration. If it is necessary to significantly change fre-quency range of the welding current (in direction ofthe frequency reduction), there is not need to replacediscrete elements of the control system. Range of the

Figure 1. Structural scheme of device for pulsed-arc welding

Figure 2. Control signal of microcontrollerFigure 3. Modulated current for pulsed-arc welding (2 A ---- 5 msscale)

12/2008 13

pulse and the pause duration regulation changes de-pending upon the program time unit.

In future it will be advisable to single out fromthe data array, obtained during performance of ex-periments in welding of metals of various thicknesses,optimal ranges of regulation of main parameters ofthe welding current for achieving established mini-mum influence of temperature, depth of penetration,

and stability of the welding process. Presented controlscheme may be used with certain amendments for asimilar welding current source of 4 kW power.

1. Baranov, V.N. (2004) Application of AVR microcontrollers:schemes, algorithms. Moscow: Dodeka-XXI.

2. Trampert, V. (2007) Measurement, control and regulationusing AVR microcontrollers. Kiev: MK-Press.

MECHANISM OF THE EFFECT OF SCANDIUMON STRUCTURE AND MECHANICAL PROPERTIES

OF HAZ OF THE ARC WELDED JOINTSON ALUMINIUM ALLOY V96

Yu.A. KHOKHLOVA, A.A. CHAJKA and V.E. FEDORCHUKE.O. Paton Electric Welding Institute, NASU, Kiev, Ukraine

Heating of base metal in arc welding of high aluminium alloy V96 leads to melting of low-melting point (eutectic)phases along the grain boundaries in HAZ. These phases are the cause of hot cracking of HAZ, while after cooling theydecrease the level of mechanical properties of the joints. Scandium additions to the alloy slow down recrystallisationprocesses, thus promoting formation of a dispersed structure of the eutectic precipitates along the grain boundaries and,consequently, improvement of mechanical properties of the joints.

K e y w o r d s : aluminium alloys, arc welding, hot shortness,structural transformations, eutectic, scandium, strength, mi-cromechanical tests, Berkovich indenter, microhardness, Youngmodulus, ductility coefficient

Heating of base metal in arc welding of high alloyV96 leads to melting of low-melting point componentsto form brittle interlayers in the fusion zone aftercooling, thus causing initiation of solidification cracks[1] (Figures 1, 2). Alloys of this type are categorisedas the strongest aluminium alloys. They are intendedfor production of light extruded and forged parts inmachine building, and used as experimental structuralmaterials [2]. Scandium, which is an expensive mate-rial, is usually added to alloy V96 to prevent initiationof solidification cracks. Scandium additions are knownto have a positive effect on mechanical properties ofaluminium alloys, which shows up in modification of

cast structure, increase in recrystallisation tempera-ture, as well as precipitation hardening and structuralstrengthening.

The effect of scandium on many advanced alu-minium alloys has been well studied up to now [3],and many scandium-containing aluminium alloys areavailable. However, the effect of scandium on theprocesses occurring in HAZ and weld metal remainslittle investigated as yet.

The purpose of this study was to investigate themechanism of the effect of scandium on improvementof structure and micromechanical properties of theeutectic formed along the fusion boundary in HAZduring arc welding.

The procedure used to conduct a set of mechanicalinvestigations provides for making of simulation speci-mens of the alloys, whose chemical and structural

Figure 1. Microstructure near HAZ of the arc welded joint on alloy V96

© Yu.A. KHOKHLOVA, A.A. CHAJKA and V.E. FEDORCHUK, 2008

14 12/2008

composition corresponds to that of the eutectic of brit-tle interlayers formed within the fusion zone of thewelds. Arc welded joints of two modifications of theV96 type alloy were used as a material for the inves-tigations. Chemical composition of initial alloys V96and V96 + Sc is given in the Table and shown in asection of the 460° isothermal tetrahedron of the Al--Mg--Cu--Zn system (8 wt.% Zn), comprising the fol-lowing phases (Figure 3) [4, 5]: α ---- Mg, Zn, Cusolid solution in Al; θ ---- CuAl2; S ---- Al2CuMg; T ----AlCuMgZn (forms Al2Mg3Zn3 and Al6CuMg4phases); M ---- AlCuMgZn (forms phases MgZn2 ofthe Mg--Zn system and AlCuMg of the Al--Cu--Mgsystem); Z ---- AlCuMgZn (forms phases Mg2Zn11 ofthe Mg--Zn system and Al10Cu7Mg3 of the Al--Cu--Mgsystem).

Scandium is characterised by low (0.35 %) solu-bility in solid aluminium. Primary intermetallicsemerge as early as at its concentration that is a bithigher than the limiting one. They form under con-ventional casting conditions and have the form ofcoarse, non-uniformly distributed inclusions [6].

The process of melting and solidification of bothalloys occurs in two stages. First the low-melting pointeutectic melts at a temperature of 480 °C. This short-time process ends quickly, and melting of the solidsolution occurs starting from 580 °C. In cooling, firstthe solid solution and then eutectic solidify [7]. Theentire solidification range is approximately 170 °C,the portion of the eutectic solidification range beinginsignificant (less than 2 %). The data obtained onformation of the eutectic in a wide temperature rangeof 480--580 °C are indicative of the probability ofoccurrence of the eutectic precipitates and embrittle-ment of the HAZ metal at a considerable distancefrom the fusion boundary, while those on a wide rangeof solidification of the alloy and low content of the

eutectic at the final stage of solidification are indica-tive of an increased sensitivity to hot cracking in theweld metal.

Fine structure of the weld metal, characterised bythe presence of continuous eutectic precipitates alongthe boundaries and cells of dendrites, is formed in

Figure 2. Microstructure of fracture along the grain boundaries at the sites of concentration of brittle interlayers of low-melting pointcomponents (×800) and near HAZ (×1200) of the arc welded joints on alloys V96 and V96 + Sc

Figure 3. Section of isothermal tetrahedron 460° of Al--Mg--Cu--Znsystem (8 wt.% Zn)

Chemical composition (wt.%) of initial alloys V96 and V96 + Sc*

Alloy Zn Mg Cu Sc Mn Zr

V96 8.4--8.8 2.5--2.7 2.4--2.6 -- 0.20--0.26 0.15--0.18

V96 + Sc 8.6--8.9 2.6--2.8 2.1--2.4 0.27--0.31 0.19--0.25 0.15--0.18

*Balance ---- aluminium.

12/2008 15

welding of alloy V96. Addition of scandium to thealloy leads to refining of grains, formation of a sub-dendrite structure, and change in the character of dis-tribution of the eutectic. Grain size in the weld metalcontaining 0.3 % Sc decreases from 0.100--0.500 to0.030--0.001 mm. The eutectic precipitates are locatedonly along the sub-dendrite grain boundaries (see Fi-gure 1). Isolated intermetallics of a regular geometricshape, 3--7 µm in size, form in the weld metal on alloyV96 + Sc.

Examination of structure of the HAZ region at aliquid--solidus temperature revealed different eutecticformations in both alloys. Their shape and size areaffected by the initial structure of the base metal. Forexample, in the case of continuous stringer-type pre-cipitates of the redundant phases the eutectic precipi-

tates are thin and extended, whereas at the presenceof isolated inclusions they form local eutectic volumes.The latter are concentrated in locations of the redun-dant phases. With distance to the fusion boundaryand increase in temperature, first the high-angle grainjunctions melt to form continuous interlayers. Withan addition of scandium to the base metal, the meltingprocess becomes less reactive. It is mostly of a localcharacter (except for extended eutectic structure for-mations), and decrease in the recrystallisation extenttakes place. Inclusions of the aluminium-scandiumphases persist in HAZ in a somewhat modified form.They are distributed both in the bulk of grains andin the eutectic clusters.

Chemical composition of the eutectic precipitatesalong the grain boundaries was determined by themethod of X-ray microanalysis of HAZ of the jointson alloys V96 and V96 + Sc made by arc weldingusing no filler wire.

Eutectic precipitates in alloy V96 had the follow-ing chemical composition, wt.%: 28 Zn, 15.9 Cu, 10.5--11.0 Mg (compact eutectic inclusions), and 27.7 Zn,16 Cu, 12.0--12.5 Mg (continuous boundary inclu-sions), i.e. the eutectics had an almost identical com-positions independently of their form. Eutectic pre-cipitates in alloy V96 + Sc were characterised by awide range of changes in the content of elements.Detailed X-ray microanalysis of different points ofthe precipitates made it possible to detect two typesof the eutectics. The first was characterised by anincreased content of the following elements, wt.%:

Figure 4. Microstructure of eutectic in simulation specimens of arcwelded joints on alloys V96 (a) and V96 + Sc (b) (×600)

Figure 5. Indentations (a, c ---- ×600) and loading-unloading diagram (b, d) for eutectics of alloys V96 (I) and V96 + Sc (II)

16 12/2008

25--27 Zn, 17.9--18.2 Cu and 11.7--12.0 Mg; and theother ---- by their decreased content (15.5--18.2 Zn,8--21 Cu and 4.6--5.3 Mg) and presence of 3.1--8.4 Sc.

Ingots that simulated structure and chemical com-position of the eutectic of melted interlayers near thefusion boundary in arc welding were melted. The in-gots of the required chemical composition were pro-duced from the alloys containing the following ele-ments, wt.%: 28 Zn, 16 Cu, 13 Mg, balance ---- alu-minium, and 17 Zn, 10 Cu, 5 Mg, 6 Sc, balance ----aluminium. The use was made of electrolytic copperand zinc, and high-purity aluminium A995. Scandiumwas added from the master alloy containing2 wt.% Sc, which was preliminarily melted in a cru-cible and then gradually cooled to room temperature.Intermetallic inclusions settled on the mould bottomto form the ingot layer containing 16 % Sc. Accordingto the data of X-ray microanalysis, the distributionof scandium in height of an ingot was as follows,wt.%: 16.600 in the lower part, 0.511 in the middle,and 0.470 in the upper part. Scandium was added tothe charge from the lower layer of the ingot. Meltingwas performed in a graphite crucible of the mufflefurnace. Molten metal was cast into a special shape,which made it possible to immediately produce speci-mens of the MI-3 type for mechanical tests and ex-amination of their structure and chemical composition.

As shown by metallographic examinations, castspecimens had primarily the eutectic structure. Thespecimens that corresponded to the Al--Zn--Cu--Mgalloy eutectic had a more non-uniform and coarse-den-drite structure (Figure 4, a). The scandium-containingeutectic was more dispersed. However, it containedisolated coarse scandium intermetallics (Figure 4, b).

Mechanical properties of the alloys correspondingto eutectics Al--Zn--Mg--Cu and Al--Zn--Mg--Cu--Scwere determined on the specimens of the above type,which fractured by the brittle mechanism without for-mation of the plasticity regions. The character of frac-ture changed from that of a deep penetration to thestraight-lined one, the eutectic having an increasedstrength value (in the presence of scandium). Strengthof the specimens of alloy V96 + Sc was 141 MPa, andthat of alloy V96 ---- 134 MPa.

Micromechanical tests were carried out with the«Micron-Gamma» computerised probe system usingthe Berkovich trihedral indenter [8, 9]. Microhardnessof the eutectic of alloy V96 of a different shape andetching ranged from 0.024 to 0.390 GPa. Light eutec-tic had the maximal value of microhardness, and theminimal value of microhardness was detected in themiddle of dark coarse secondary dendritic structures(Figure 5, a). Microhardness of alloy V96 + Sc was0.325--1.324 GPa, and that of the dark phase was1.324 GPa. Microhardness of isolated coarse scandiumintermetallics differed but insignificantly from thatof the scandium-containing eutectic (Figure 5, b), thevalues of Young modulus being 40 % higher comparedwith the scandium-containing eutectic. The values ofmicrohardness of the eutectic of alloy V96 + Sc were41 % higher than those of alloy V96. The ductilitycoefficient of the eutectics remained at the same level.

Therefore, embrittlement in welding of alloy V96occurs at a substantial distance from the fusion bound-ary. Scandium additions to alloy V96 slow down therecrystallisation processes and decrease the liquationlevel. Modification of the alloy leads to improvementof its structure and preservation of ductility, and pro-vides increase of 41 % in microhardness, 40 % in Youngmodulus, and 5 % in strength.

1. Ovsyannikov, B.V., Doroshenko, N.M., Zamyatin, V.M.(2005) Solidification cracks in ingots of high-strength alu-minium alloys. Tekhnologiya Lyog. Splavov, 1--4, 117--121.

2. Fridlyander, I.N. (2002) Aluminium alloys in aircraft of the1970--1999 and 2000--2015 periods. Ibid., 4, 12--17.

3. Fridlyander, I.N., Chuistov, K.V., Berezina, A.L. et al.(1992) Aluminium-lithium alloys. Structure and properties.Kiev: Naukova Dumka.

4. Mondolfo, L.F. (1979) Structure and properties of alu-minium alloys. Moscow: Metallurgiya.

5. (1977) Constitutional diagrams of aluminium- and magne-sium-base systems: Refer. Book. Moscow: Nauka.

6. Volkov, V.A. (1987) Effect of alloying elements on theprocesses of decomposition of Al--Li and Al--Sc alloys: Syn.of Thesis for Cand. of PhM Sci. Degree. Kiev.

7. Berezina, A.L., Volkov, V.A., Domashnikova, B.P. et al.(1987) Some peculiarities of decomposition of oversaturatedsolid solution of Al--Sc system alloys. Metallofizika, 9(5),43--45.

8. Grigorovich, V.K. (1976) Hardness and microhardness ofmetals. Moscow: Nauka.

9. Oliver, W.C., Pharr, G.M. (2004) Measurement of hardnessand elastic modulus by instrumented indentation: advancesin understanding and refinements to methodology. J. Mater.Res., 19, 3--20.

12/2008 17

LASER-ASSISTED HARDENINGAND COATING PROCESSES (REVIEW)

V.Yu. KHASKINE.O. Paton Electric Welding Institute, NASU, Kiev, Ukraine

The paper considers the state-of-the-art in the field of heat hardening, alloying, cladding and coating processes, in whichthe main role is given to laser radiation. Flow diagrams of the above processes are presented, and their advantages anddisadvantages are noted. Prospects for further development of these processes are analysed by examples of their practicalapplication.

K e y w o r d s : laser technologies, heat treatment, alloying,cladding, coating, hybrid and combined processes, advantagesand disadvantages, practical application, prospects for develop-ment

Laser-assisted processes are of an increasingly wideinterest to deposition of functional coatings [1, 2].They include laser (cladding and surface modifica-tion), as well as hybrid or combined (laser-plasmacoating, laser treatment with high-frequency heating,etc.) processes. These processes are implemented byusing radiation of technological lasers: gas (CO2-la-ser), solid-state (Nd:YAG-laser), diode (Table 1) andfibre ones [3]. Based on the chronology of emergence,the laser-assisted processes can be ranked as follows:heat treatment, alloying, cladding, spraying, and hy-brid welding.

Laser heat treatment consists in affecting a work-piece by the focused laser beam, and can be imple-mented with or without melting of the surface treated.In the latter case, it is necessary to preliminary depositcoatings that absorb the laser radiation [4, 5]. Mainadvantages of this process include locality of the heateffect (the heating spot is normally 0.1--10.0 mm insize), flexible power supply to the treatment site, andpossibility of producing layers with high hardness andwear resistance, modified to a depth from several mi-crometers to 1--3 mm [6]. As this process is accompa-nied by refining of grains, it allows hardening of met-als without formation of hard phases. Disadvantages

of the process include formation of internal stressesalong the hardening strips, which may lead to crack-ing, as well as probability of pore formation in hard-ening with melting due to evolution of gases causedby burning out of non-metallic inclusions from thebase metal [5, 7]. The presence of gases leads to for-mation of bubbles in the molten pool metal, and be-cause of a short time of existence of the pool thebubbles have no time to escape to the surface.

One of the first ingenious developments utilisingto the full extent the optical advantages of laser ra-diation for the heat treatment processes is special op-tics, which integrates the energy with the help of asegmented mirror by superimposing many separate ele-ments of the beam [8]. Microprocessor-controlledscanning heads were developed at the end of the 1980s,which were used for laser heat treatment and cladding.Scanning of the laser beam has often been used up tonow to uniformly distribute the energy for treatmentof complex-configuration workpieces [9], thus provid-ing substantial flexibility of the heat hardening andcoating processes.

Laser alloying is intended for forming a compara-tively small (approximately 0.2--0.6 mm in diameterand 0.1--3.0 mm deep) molten pool on the surfacetreated, with metallic and non-metallic (e.g. gaseous)alloying elements added to it [4, 5, 10--12]. As a resultof movement of the heat source relative to the surfacetreated, a layer with modified physical-chemical char-

© V.Yu. KHASKIN, 2008

Table 1. Parameters of different types of high-power lasers used for hardening and coating processes

Laser parameters CO2-laserPumped Nd:YAG laser

Diode laser

Lamp-pumped Diode-pumped

Wavelength, µm 10.6 1.06 1.06 0.8--0.94

Efficiency, % 5--10 1--3 10--12 30--50

Maximal power, kW 40 4 4 6

Average power density, W/cm2 1⋅106--1⋅108 1⋅105--1⋅107 1⋅106--1⋅109 1⋅103--1⋅105

Interval between service maintenances, h 2000 200 10000 10000

Transmission of radiation via optic fibre No Yes Yes Yes

Quality of radiation, mm⋅mrad 12 25--45 12 100--1000

18 12/2008

acteristics is formed on the latter. Advantages of laseralloying include [4, 5] the possibility of alloying themetal surface to a depth of 2--3 mm to form bothchemical compounds and solid solutions of alloyingelements in the metal structure, formation of struc-tures with a high dispersion degree and minimal heat-affected zone (HAZ) owing to minimisation of theheat effect on the substrate, and substantial reductionof residual strains, compared with the plasma method.Drawbacks of this process are similar in many respectsto those of laser heat treatment. The difference consistsin the formation of pores, blowholes and splashescaused by addition of alloying elements (gaseous ones,in the first turn) to the molten pool.

Laser cladding as a method for deposition of coat-ings originates from laser alloying, which was devel-oped a bit earlier [4, 5, 10--12]. In cladding, a coatingof the preset thickness with the preset physical-chemi-cal characteristics is formed on the surface treated dueto feeding a cladding consumable (mostly in the formof powder, or more rarely ---- in the form of wire) tothe zone affected by the laser beam focused into a spot1--5 mm in diameter. This process may have modifi-cations, including laser cladding on the cladding con-sumable layers preliminarily deposited on the sub-strate. These layers are first produced by thermalspraying or by using a covering consisting of a claddingpowder and binder, and then they are remelted byusing the laser beam [13]. Cladding on the prelimi-narily deposited layers is usually called laser remelting[14]. The resulting coating adheres to the substratematerial through a transition zone of a comparativelysmall size (5--10 to 50--200 µm) [4]. Strength of ad-hesion of the coating to the base metal is sufficientlyhigh, and is close to strength of the latter.

One of the important points of the cladding tech-nology is the method of feeding a cladding materialonto the substrate. As shown by investigations of lasercladding and welding methods, whereas treatment bythe wire cladding process can be realised almost inany spatial position, the advantage of powder consu-mables consists in a more efficient absorption of laserradiation [15]. Flat cladding can be performed bypreliminarily distributing the powder over the surfacetreated [16]. Application of powder consumables inother spatial positions normally requires that the coat-ings be deposited by flame [17] or plasma spraying[18], or by furnace drying of the paste-like covering[19]. If a powder cannot be preliminarily distributedover the surface of a workpiece, it should be fed byusing special feeders during the cladding process. Atpresent, a wide acceptance has been received by lasercladding using powder additives fed directly to zoneaffected by the laser beam from special powder feedersof different designs [20].

Advantages of laser cladding include the possibil-ity of deposition of the clad layers with preset prop-erties from 0.1 to 3.0 mm thick [4, 5]; considerablemitigation of the effect of redistribution of compo-nents from the substrate material to deposited layer,

thus providing a better accuracy of prediction of theresults and properties of the deposited layers as closeas possible to those of the base material [4, 19]; for-mation of equiaxed fine-crystalline (highly refined)structures of the deposited metal and a small size (upto 0.1--0.5 mm) of HAZ [21]; and minimisation ofallowance for final machining, the size of which isabout 0.3--0.5 mm on each side, due to a low (200--300 µm) roughness of the surface treated [22, 23].

Drawbacks of laser cladding include the presenceof transverse cold microcracks in the deposited andmicrolalloyed layers, which are formed as a result ofrelaxation of high tensile stresses [14]; possibility offormation of both internal and external pores causedby the presence of non-metallic inclusions, residualmoisture contained in the cladding powder and con-tamination of the surface treated; and comparativelyhigh cost of the process resulting from a high cost oflaser equipment [4, 5]. The issues of monitoring, de-creasing and complete elimination of cracking in lasercladding were investigated in different times by manyauthors (e.g. [4, 5, 14]). Comparatively recently, theUkrainian scientists have suggested a mathematicalmodel for this phenomenon, which relates distancebetween the cracks to mechanical properties of thecoatings and their thickness [24]. As follows from theabove-said, the promising methods for elimination ofthe process drawbacks are those that combine reduc-tion of residual thermal stresses in the deposited layersand careful preparation of the powder additives andsurfaces being treated. Such methods include, in par-ticular, modification of the thermal cycle of the clad-ding process through using an additional heat source(e.g. the laser beam combined with the plasma jet).

Laser cladding is used to produce wear- and cor-rosion-resistant microcrystalline, amorphised andamorphous coatings from a very wide range of mate-rials [21]. However, in the first half of the 1980s thelaser cladding technology was applied primarily forrepair of worn-out parts operating under conditionsof sliding friction, impact loads, abrasive wear, etc.[4, 5, 22, 23]. Reconditioning laser cladding has notlost its topicality up to now even in industrialisedcountries [25]. Moreover, the technology was devel-oped for underwater laser cladding [26].

Intensive research was carried out in the 1980s onthe process of laser thermal spraying [27, 28]. But asthe coatings produced by this method were close intheir properties to those produced by plasma weldingmethods, further on this process became less popularthan laser cladding. Spraying consumables for thisprocess are powders and wires fed at a speed of 0.5--11.0 m/min (Figure 1). Spraying can be carried outat a speed of 0.5--5.0 m/min and distance betweenthe head and workpiece equal to 50--150 mm by usingthe 1--5 kW CO2-laser [27]. The process gas fed at apressure of 0.1--0.5 MPa can be either inert (e.g. ar-gon) or reactive (nitrogen, oxygen). There is a modi-fication of powder spraying by laser, which includesheating of a spraying powder with the laser beam [28].

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Differences between the processes of flame spraying,laser cladding and laser powder spraying are demon-strated in Figure 2. With laser cladding the heatingspot is just a bit smaller than with laser spraying.However, in the latter case there is no direct impactby the beam on the substrate, which increases localityof the heat effect. Strength of adhesion of the sprayed

layers to the substrate is inversely proportional tothickness of the layers. Study [29] dedicated to mathe-matical modelling of laser powder spraying presentsthe calculations made for the two most promisingmodifications of the process, i.e. with coaxial feed ofthe radiation and powder, and with heating of thepowder by the radiation (Figure 2, c).

The process flow diagram shown in Figure 1, usingwire feeding without a powder, was employed for laserspraying of titanium and titanium nitride on a steelsubstrate by spraying titanium wire in the Ar + N2gas mixture to produce heat-resistant coatings [30].Because of a lower cost of wire compared with pow-ders, the use of wire for laser spraying allows the costof this process to be reduced. However, it should benoted that coatings deposited by this method are closein their properties to those produced by arc metallising[31]. Advantages of laser spraying are similar to thoseof the thermal (e.g. microplasma) spraying processes[32]. The major drawbacks of this process are thenecessity of subjecting the surface treated to prelimi-nary jet-abrasive blasting, and a much lower strengthof adhesion of the deposited layers to the substrate,compared with laser cladding.

At present the laser spraying method is applied toproduce thin coatings with the amorphous or crystal-line microstructure, having roughness that matchesroughness of the surface treated [33]. Such coatingsare characterised by properties of both metals andsemiconductors. Another promising area of develop-ment of this method is deposition of ceramic coatings,i.e. laser spraying of aluminium oxide [34]. In thiscase the coatings can be applied to a sub-layer, e.g.of nickel alloys.

Another aspect of application of laser spraying isprecision synthesis of 3D parts. The authors of study[35] propose to use robot to produce almost any 3Dparts from metal, ceramic or polymer powders. Thesynthesis processes were developed on the basis ofselective laser sintering [36]. One of the most prom-ising areas today is the DMD (direct metal deposition)technology, which is employed most often for manu-

Figure 1. Flow diagram of the laser spraying process involving wirespraying and powders additionally fed to produce composite coat-ings: 1 ---- powder feed; 2 ---- nozzle; 3 ---- spraying wire; 4 ---- gas;5 ---- laser beam; 6 ---- spraying jet; 7 ---- substrate

Figure 2. Flow diagrams of the processes of thermal spraying (a), laser cladding (b) and laser powder spraying (c) [26]

20 12/2008

facture of dies and moulds (Figure 3). In contrast tothe process described in [35], the DMD technologycan be regarded as 3D laser cladding, rather thanspraying. During the DMD process the laser beam isfocused on a metal billet, i.e. 3D mould (a piece thatapproximately copies the shape of a workpiece), oron a damaged metal part, where it forms the moltenmetal zone. A thin jet of the metal powder is injectedwith the help of a transportation gas to the moltenzone. The all-metal part is formed layer by layer as aresult of computer-controlled movement of the laserbeam and powder jet in accordance with the CAD(computer aided design) model.

Another method of laser coating is vacuum laserdeposition, which is also called the laser-plasma spray-ing. When using the modulated laser beam, durationof its pulses may be 60--350 s at a power density ofup to 2--5 GW/cm2. This method is employed to spraythin (less than a micrometer) films. Examples of sur-face deposition of films can be thin films of high-tem-perature superconductors, films of such materials asGaAs, InGaAs, PbTe, Bi, ZrO2, SrTiO3, ZnO, as wellas diamond-like films [37]. Thin surface films are pro-duced by using laser radiation in the CVD (chemicalvapour deposition) and PVD (physical vapour depo-sition) processes [38]. As a rule, here the laser beamplays an auxiliary role to improve the existing proc-esses, which can be seen from their names: LACVD(laser assisted CVD) and LEPVD (laser enhancedPVD). Advantages of these processes include the pos-sibility of achieving high physical-mechanical propertiesof a coating, formation of surfaces that need no sub-sequent finishing and have roughness identical to thatof the substrate; and drawbacks include the presence ofspecial chambers and vacuum equipment, complexity ofpreparation of a workpiece for coating deposition, andundesirable deposition of a consumable on the surfaceof the equipment inside the vacuum chambers.

Development efforts are active now on such com-bined processes as cladding, coating and heat treat-ment performed by laser with concurrent high-fre-quency heating [39]. The process of laser inductioncladding can be implemented by the similar flow dia-gram (Figure 4) at the presence of a feeder that feedsa cladding powder.

One of the examples of application of laser induc-tion heat treatment is surface remelting of cast ironcams to produce a wear-resistant ledeburite layer. Thehigh-frequency process component allows eliminatinginternal residual stresses and microcracks in the modi-fied layer. It is this factor (along with the possibilityof considerably increasing the speed of treatment ordecreasing the laser power) that is the main advantageof the laser induction processes. Their drawbacks in-clude volumetric heating of a workpiece to high (500--1000 °C) temperatures, which may lead to thermaldeformations. Therefore, it is reasonable to apply thecombined laser-induction treatment to axisymmetricpieces (e.g. bodies of revolution). Another drawback

is a high energy intensity of the combined process.The constant electric field can also be used in suchprocesses, in addition to the high-frequency electro-magnetic field.

Modifications of the combined treatment involvinglaser radiation are laser-light technologies [40]. Thelight-beam technologies were actively developed inthe 1970--1980s [41]. The light-beam treatment meth-ods are applied to advantage for welding and brazing(e.g. car radiators). But this process is of the highest

Figure 3. Flow diagram of the process of 3D synthesis of parts bythe DMD technology: 1 ---- CO2-laser radiation; 2 ---- focusingoptics; 3 ---- powder feeding; 4 ---- shielding gas; 5 ---- sensors ofoptical feedback system; 6 ---- piece being formed; 7 ---- billet ormould; 8 ---- platform

Figure 4. Flow diagram of laser induction heat treatment and clad-ding with concurrent high-frequency heating [39]: 1 ---- laser ra-diation; 2, 3 ---- focusing and scanning optics, respectively; 4 ----inductor; 5 ---- shaped laser beam; 6 ---- workpiece regions heatedby means of inductor; 7 ---- workpiece

12/2008 21

interest to heat treatment, including the combinedlaser-light one [40]. In the latter case the light-beamheating plays the same role as the induction or electricone, although it has such a drawback as increasedpower intensity.

In the last decade the purely laser technologieshave been progressively replaced by the hybrid andcombined ones. They include the laser-plasma proc-esses using the combined action of the arc plasma andlaser heat source. Investigations of the processes ofinteraction of the focused CO2-laser beam with theelectric arc plasma column, which were conducted bythe E.O. Paton Electric Welding Institute, show thata special type of the gas discharge, i.e. the combinedlaser-arc one, can be formed in this system [42]. Itsproperties differ from properties of both electric arcand optical discharge maintained by laser radiation.Ability of the combined discharge to generate the high-temperature plasma with a high degree of non-equi-librium (non-isothermicity) even at the atmosphericpressure of an ambient gas makes it attractive forapplication with plasma-chemical technologies, in-cluding the CVD ones. Theoretical and experimentalstudies conducted by the E.O. Paton Electric WeldingInstitute show that the above properties of the com-bined discharge can be used as a basis for developmentof a new class of plasma devices, i.e. integrated laser-

arc plasma torches [43, 44]. A range of integratedlaser-arc direct- and indirect-action plasma torches,which are unique for the world practice, is availablefor such new hybrid processes as laser-microplasmawelding, cladding and spraying, as well as hybridlaser-plasma deposition of diamond and diamond-likecoatings developed by the E.O. Paton Electric Weld-ing Institute [44].

The trend in development of the laser-plasma proc-esses is towards modification of surfaces and deposi-tion of coatings 0.1--3.0 mm thick [45, 46]. Laser-plasma hardening and thermal strengthening are astriking example of surface modification [45]. Thisprocess is similar in many respects to laser heat hard-ening [4--6]. The main difference lies in the possibilityof replacing a certain portion of the laser energy bythe arc plasma energy. Of high interest are the proc-esses of laser-plasma spraying (Figure 5). They com-bine the effect of laser heating of the surface andplasma coating deposition, where focusing spot 3 ofthe laser beam is combined with coating formationzone 5 (Figure 5) [46]. This technology is called thelaser assisted atmospheric plasma spraying [47]. Thisprocess provides a dense layer characterised by in-creased adhesion strength. Companies LERMPS-IPSeand IREPA-Laser developed and patented the PRO-TAL technology, which provides the effect of surfacepreparation by ablation of the substrate surface layerdue to incomplete overlapping of the plasma sprayingzone by the laser heating zone. As a result, there isno need to use jet-abrasive blasting [47, 48].

Following the Japanese and French scientists [48],investigations of the laser-plasma spraying process werealso carried out in Germany (Fraunhofer Institute), Rus-sia and Ukraine. In particular, the plasma-laser fixtureand technologies for production of coatings by usingdynamic focusers were developed in Russia [49]. TheUkrainian scientists [50] suggested a mathematicalmodel, describing motion and heating of powder parti-cles in laser, plasma and hybrid spraying.

Experiments were conducted on application of thecombined laser-plasma processes for depositing cuttingtools with the coatings characterised by increased heatand wear resistance, as well as decreased coefficients ofsliding friction under contact service loads [45].

Figure 5. Flow diagram of combined laser-plasma spraying of coatings [46]: 1 ---- sample; 2 ---- powder transporting plasma jet; 3 ----laser radiation; 4 ---- deposited layer; 5 ---- coating formation zone

Figure 6. Flow diagram of the optimised proportion of geometricparameters of the process of laser-plasma powder cladding usingNd:YAG laser radiation (workpiece ---- anode) [54]

22 12/2008

In Ukraine, the priority in the field of combinedlaser-plasma deposition of coatings belongs to theE.O. Paton Electric Welding Institute, which hasbeen active in this area since the beginning of 2000[44]. Initially, the investigations were conducted byusing continuous CO2-lasers, in contrast to the foreigndevelopments involving pulsed Nd-YAG laser [46] orcontinuous Nd:YAG and diode lasers [51]. At present,the E.O. Paton Electric Welding Institute is masteringthe laser-plasma coating techniques by using the abovetypes of the lasers. The hybrid coating method, wherethe laser beam is transmitted along the plasma axis,is more advanced in terms of a combined use of thelaser and plasma energy [42, 43, 52]. Transportationof the powder material in this case is implementedwith preliminary heating by the energy of the laser-plasma discharge [51]. Unlike the hybrid method, themethod shown in Figure 5 should be regarded as acombined one. In this case, only the plasma energy isused to heat the spraying powder.

The laser-plasma cladding technology is being up-graded now, in addition to the laser-plasma sprayingone. This process uses the direct-action plasma torchesand mostly powder consumables [53]. Its main advan-tage is additional constriction of the plasma arc bythe focused laser beam (Figure 6). The authors ofstudy [54] are of the opinion that the pulsed radiationof Nd:YAG-lasers is most promising for this purpose,as it can be flexibly fed via an optic fibre in theoptimised spatial position. Compared with laser clad-ding, the laser-plasma cladding process makes it pos-sible to substantially reduce residual stresses in thedeposited layers. However, one of its main drawbacksis still a high thermal effect on a workpiece.

Analysis of advantages and disadvantages ofplasma, laser and laser-plasma cladding and sprayingprocesses shows the following. Peculiarities of themajority of the plasma spraying processes are the ne-cessity to employ preliminary surface preparation(most often, jet-abrasive blasting), use of sub-layersin a number of cases, and some discontinuity (micro-porosity) of the coatings (Table 2).

In the case of plasma cladding, a workpiece mayexperience a high heating, which leads to residualthermal deformations. The laser and laser-plasmaprocesses make it possible to minimise heating of aworkpiece, increase the strength of adhesion of thedeposited layers to the substrate, use no sub-layers,and simplify the surface preparation operation. At thesame time, the laser cladding processes have somedrawbacks, such as the stressed state of the depositedlayers and presence of pores and microcracks in them.The hybrid (combined) laser-plasma processes are par-tially or fully free from the above drawbacks, whichis provided by interaction of their components or theircombined effect on workpieces. For example, constric-tion and stabilisation of the plasma arc by laser ra-diation allows increasing the process speed and de-creasing the total heat input; preliminary heating ofthe powder with the combined discharge, along withmodification of the thermal cycle of the laser treatmentprocess due to addition of the plasma component, al-lows reducing residual stresses, eliminating pore andcrack formation; and cleaning of the workpiece surfaceby laser ablation and its melting make the preliminarysurface preparation operation simpler, etc.

Therefore, analysis of the processes of laser andhybrid (combined) hardening and coating depositionshows that owing to their application it has becomepossible to produce corrosion- and wear-resistant coat-ings with improved physical-mechanical properties,provide synthesis of 3D objects, and deposit thin films(e.g. diamond and diamond-like) characterised by spe-cial properties. Prospects for further development ofthe laser-plasma (laser-arc) processes of surface modi-fication and coating deposition relate to eliminationof drawbacks inherent in each of their componentstaken separately (laser and arc heat sources), as wellas to increase in the efficiency of their interaction.

1. Grigoriants, A.G., Misyurov, A.I. (2005) Possibilities andprospects for application of laser cladding. TekhnologiyaMashinostroeniya, 10, 52--56.

2. Kovalenko, V.S. (2001) Laser technology at a new stage ofdevelopment. The Paton Welding J., 12, 3--8.

Table 2. Comparison of characteristics of laser and thermal spraying processes

Coating process characteristic Thermal spraying Laser coating

Heat source Gas flame, electric arc or plasma High-intensity laser radiation

Coating to substrate bond Mechanical bond of low or moderate strength* High-strength metallurgical bond

Coating structure Lamellar; from porous to almost dense* Dense; crack- and pore-free layers

Thermal load on working zone Low temperature of heating* Insignificant heating

Dilution of substrate metal No Insignificant

Coating thickness From 0.05 to several millimetres 0.5--3.0 mm

Coating material Wide range of metals, alloys, hard metals,ceramics and polymers*

Metals and alloys; alloys with hard particles;hard metals; ceramics

Productivity From low to high* From low to moderate/(high)*

Cost From low to high* From moderate to high

*Depending upon the process type.

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3. Vuoristo, P., Tuominen, J., Nurminen, J. (2005) Laser coat-ing and thermal spraying ---- process basics and coating prop-erties. In: Proc. of ITSC (Basel, Switzerland, May 2--4,2005), 1270--1277.

4. Grigoryants, A.G., Safonov, A.N. (1987) Laser techniqueand technology: Refer. Book. Book 3: Methods of surface la-ser processing. Ed. by A.G. Grigoriants. Moscow: VysshayaShkola.

5. Abilsiitov, G.A., Golubev, V.S., Gontar, V.G. et al. (1991)Technological lasers: Refer. Book. Vol. 1: Calculation, de-sign and service. Ed. by G.A. Abilsiitov. Moscow: Mashi-nostroenie.

6. Khaskin, V.Yu., Pavlovsky, S.Yu., Garashchuk, V.P. et al.(2000) Properties of hypereutectoid complex-alloyed steelsafter laser heat treatment. The Paton Welding J., 5, 51--54.

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8. Dourte, D., Spawr, N.J., Pierce, R.L. Optical integrationwith screw supports. Pat. 4195913 US. Publ. 04.80.

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12. Katayama, S., Matsunawa, A., Arata, Y. (1986) Laser ni-triding and hardening of titanium and other materials. In:Proc. of Int. Conf. on Electron and Laser Beam Welding(Tokyo, July 14--15, 1986). Oxford, 323--324.

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50. Borisov, Yu.S., Bushma, A.I., Krivtsun, I.V. (2005) Modellingof movement and heating of powder particles in laser, plasmaand hybrid spraying. Dopovidi NAN Ukrainy, 1, 86--94.

51. Beyer, E., Nowotny, S. Method for applying a coating bymeans of plasma spraying while simultaneously applying acontinuous laser beam. Pat. 6197386 US. Publ. 06.03.2001.

52. Devoino, O.G., Kardapolova, M.A., Krivtsun, I.V. et al.(2007) Structure and microhardness of coatings of high-chromium cast iron powder in hybrid spraying and plasmaspraying with subsequent laser glazing. In: Proc. of 3rd Int.Conf. on Laser Technologies in Welding and MaterialsProcessing (Katsiveli, Crimea, Ukraine, 29 May--27 June,2007). Kiev: PWI, 19--23.

53. Hai-ou Zhang, Ying-ping Qian, Gui-lan Wang (2006) Studyof rapid and direct thick coating deposition by hybridplasma-laser manufacturing. Surface & Coatings Technol.,201, 1739--1744.

54. Wilden, J., Bergmann, J.P., Dolles, M. (2005) Riporti su-perficiali laser: aumento di efficienza e flessibilita tramiteprocessi ibridi. Riv. Ital. Saldatura, Nov.--Dic., 809--816.

24 12/2008

DETERMINATION OF CYCLIC FATIGUE LIFEOF MATERIALS AND WELDED JOINTS

AT POLYFREQUENCY LOADING

V.S. KOVALCHUKE.O. Paton Electric Welding Institute, NASU, Kiev, Ukraine

Procedure and analytical dependences are proposed for calculation of cyclic fatigue life of materials, as well as weldedjoints at polyfrequency loading by the initial data, corresponding to the single-frequency loading. Conducted experimentalverification of the derived dependences on large-scale samples, including welded samples, confirmed their validity in abroad range of variation of polyfrequency loading parameters, the spectrum of which consists of 3--7 components.

K e y w o r d s : metal structures, welded joints, polyfrequencyloading, cyclic fatigue life, calculation

Elements of bridges, crane beams, products of trans-portation and power engineering, ships, aircraft andmany other metal structures during operation are ex-posed to simultaneous impact of several alternatingloads differing in amplitude and frequency. In thegeneral case these loads, due to the impact of externaland inner factors, can vary arbitrarily in time, and beof a random nature. In particular, span structures ofbridges are loaded by car and railway transport; off-shore deep-water platforms are exposed to sea waves;metal structures of tower type constructions, tubularstructures are exposed to the impact of inner and outerpressure, as well as air or gas flows.

With the essential difference in the frequencies ofindividual loads with a random change of amplitudesand phases, such loading patterns of a complex spec-trum can be presented in a simplified form by deter-ministic polyfequency modes, having a simple cycleform:

F(t) = ∑ i = 1

n

fi(t)

or polyharmonic modes (Figure 1), in which all thecomponents change by the polyharmonic law:

F(t) = ∑ i = 1

n

Ai sin (ωit + ϕi),

where Ai, ωi are the amplitudes and angular frequen-cies of the harmonic components, respectively; ϕi arethe initial phases (frequency and initial phase of eachcomponent usually are random values in a certain fre-quency band ωmin ≤ ω ≤ ωmax and phase interval of0 ≤ ϕ ≤ π).

Since individual elements of mechanically coupledsystems differ by filtering (selective) properties, thewideband loading spectrum usually excites a relativelynarrowband reaction in them. In many constructionsonly the loads with the lowest frequencies are of pre-

vailing importance, as with increase of componentfrequency in the above-resonance loading region theirlevels decrease markedly. This enables a schematicpresentation of the actual loading of such items bypolyfrequency modes, restricting ourselves to two toseven spectral components in many cases.

At polyfrequency loading the individual compo-nents can vary essentially in frequency, so that thefatigue resistance of materials and welded joints candepend not only on the interrelation of componentparameters, but also on the nominal frequency values.

The available local and foreign experimental datashow that additional superposition of the high-fre-quency component on the main cycle of variable load-ing leads to accelerated damage accumulation and in-tensive lowering of the cyclic fatigue life of materialsand welded joints. In particular, at bifrequency load-ing it is established that the adverse influence of thesecond component is enhanced with increase of therelative values of its amplitude and frequency [1, 2].It may be supposed that increase of the load spectrumcomposition will also be accompanied by lowering ofthe product life. However, quantitative determinationof fatigue resistance of materials and joints at poly-frequency loading is difficult. This is due, first of allto the fact, that the existing approaches to assessmentof the material cyclic life at complex alternating load-ing patterns are usually based on the hypothesis oflinear summation of damage. The dependences calcu-lated on its basis are in satisfactory agreement withthe experimental data only for some values of rela-tionships of parameters and materials, but in mostcases they can lead to considerable errors [3, 4]. Sug-gestions based on the use of nonlinear dependences ofdamage summation, energy transformation and energytheory of fatigue fracture do not provide an acceptableaccuracy, either [4].

Numerous experimental data obtained on struc-tural steels of different classes and strength levels andtheir welded joints showed [5] that the coefficient offatigue life lowering under the conditions of bifre-quency loading κ1-2 can be found from the followingrelationship:

© V.S. KOVALCHUK, 2008

12/2008 25

κ1-2 = N1/N1−2 = (f2/f1)ϑ(σa2/σa1), (1)

where N1, N1-2 are the fatigue lives measured by thenumber of load cycles up to initiation of fatigue crackof certain size at the same levels of stresses of single-frequency loading and low-frequency component ofbifrequency loading, respectively; f1, f2 are the fre-quencies; σa1, σa2 are the amplitudes of the low- andhigh-frequency components, respectively; ϑ is the co-efficient of proportionality, dependent on the materialmechanical properties.

If the material, kind of joint, stress concentration,residual stresses, cycle asymmetry, temperature, fa-tigue fracture criterion and other conditions of single-and bifrequency loading are identical, coefficient κ1-2is invariant to the above parameters at all the stresslevels in the range between the endurance and yieldlimits of the material. This enables determination ofthe cyclic life at bifrequency loading N1-2 from theavailable calculated or experimental values of fatiguelife N1 corresponding to single-frequency loading:

N1-2 = N1/κ1-2. (2)

It may be assumed that a certain dependence of thecoefficient of fatigue life lowering exists also at a largenumber of simultaneously acting alternating loads, i.e.at polyfrequency loading. Then, having the data on thevalue of this coefficient at the respective parameters ofpolyfrequency loading, the cyclic life of materials andjoints can be determined in a similar fashion. However,finding such coefficients experimentally is complicatedby an unlimited number of possible combinations ofamplitude, frequencies, and components. In addition,the law of damage accumulation at one or several com-ponents of the cyclic stress spectrum has not been es-tablished so far, particularly at the stage of fatigue crackinitiation.

Establishment of a functional dependence betweenthe parameters of polyfrequency loading and coeffi-cient of variation of cyclic life can be essentially sim-plified, if the regularities of damage accumulation un-der the conditions of single- and polyfrequency load-ing are similar. As regards the bifrequency loading,the conclusion about the similarity of these regularitiesfollows from analysis of the earlier derived results ofexperimental studies of structural materials and

Figure 1. Cycle shape at harmonic a1, b1 and polyharmonic loading with 2 (a2, b2)--5 (a5, b5) components: I ---- initial phases of all thecomponents of ϕ = 0; II ---- initial phase of the basic component b1 is equal to ϕ = 0, of all the other phases ϕ = π

26 12/2008

welded joints. In this case, the invariance of coefficientκ1-2 to a number of design, technological and servicefactors is attributable to similar manifestation of theirinfluence on the fatigue processes both at single- andat bifrequency loading. In the latter case, the cyclicfatigue life decreases only under the impact of anadditional high-frequency component, this leading atfixed values of amplitude and frequency relationshipsto parallel shifting of the initial S--N curve into theregion of lower fatigue life, and of the kinetic diagramof fatigue fracture ---- into the region of higher ratesof fatigue crack propagation. Parallel arrangement ofS--N curves or fatigue fracture diagrams points to thefact that the regularities of the processes of damageaccumulation on the same levels of single- and bifre-quency loading are similar and differ only by the co-efficients of proportionality. It follows that at a fixedlevel of alternating stresses and one fatigue fracturecriterion, which a fatigue crack of certain dimensionsusually is, the fatigue damage accumulated under theconditions of single- and bifrequency loading, is thesame. Evidently, it makes sense to assume a condi-tional or real fatigue crack of length L as the accu-mulated damage criterion. In this case, comparison offatigue testing results can be performed by averagevalues of the levels of accumulated damage from in-dividual alternating load cycles, without allowing forthe material damageability kinetics, which dependson many factors for each kind of loading taken sepa-rately. Then the average damage rate per one cycle ofalternating loading V on σa stress level can be foundfrom the following expression:

V = L/N, (3)

where L is the accumulated damage, equivalent to thereal or conditional fatigue crack, expressed in unitsof length (depth or area); N is the cyclic fatigue lifebefore damage accumulation L, expressed by the num-ber of load cycles.

With such an approach the accumulated damageunder the conditions of single-frequency loading canbe presented in the following form:

L1 = V1N1, (4)

and under bifrequency loading in the form of

L1-2 = V1-2N1-2. (5)

It is obvious that fatigue damage at bifrequencyloading is caused by the simultaneous action of N1cycles of the basic, usually low-frequency loading,and N2 cycles of superposed load smaller in magnitude,but of a higher frequency. In this case, the total dam-age value is equal to

L1-2 = L1 + L2. (6)

Considering that in order to determine the coeffi-cient of fatigue life lowering at bifrequency loading,the compared cycle numbers N1 and N1-2 should beselected at the same values of fatigue crack lengths

L1 = L1-2, equality of their values V1N1 = V1-2N1-2taking into account expression (1) yields the followingdependence:

V1-2/V1 = κ1-2. (7)

From expression (7) it follows that the averagerate of fatigue damage accumulation at bifrequencyloading is κ1-2 times higher than at single-frequencyloading. To evaluate the degree of the influence ofeach component of bifrequency loading on the processof fatigue damage accumulation, it is necessary tocompare the damage accumulated under the conditionsof single- and bifrequency loading at the same numberof cycles of single-frequency loading and low-fre-quency component of bifrequency loading, i.e. N1 == N1-2. Then the damage from the low-frequency com-ponent L1 can be found from expression (4), and thatfrom high-frequency component L2 ---- from relation-ship

L2 = L1-2 -- L1 = V1-2N1-2 -- V1N1 = N1(V1-2 -- V1).

After replacement in this expression of V1-2 = V1κ1-2by its value from expression (7), damage L2 can beexpressed as L2 = N1V1(κ1-2 -- 1), and taking (4) intoaccount ---- in the form of

L2 = L1(κ1-2 -- 1). (8)

This expression shows that the process of fatiguedamage accumulation L2 from the additional high-fre-quency component proceeds (κ1-2 -- 1) times more in-tensively than that from the basic low-frequency com-ponent of bifrequency loading. On this basis totaldamage caused by simultaneous action of the low- andhigh-frequency components of bifrequency loading,can be presented as

L1-2 = L1 + L1(κ1-2 -- 1) = L1κ1-2, (9)

and the average rate of their accumulation in the formof

V1-2 = L1κ1-2/N1-2. (10)

By analogy with the bifrequency loading, the totalfatigue damage accumulated at polyfrequency load-ing, can be determined as the sum of damage from allthe components

L1--n = L1 + L2 + … + Ln. (11)

After substitution into expression (11) of the re-spective values and simple transformation, the de-pendence for determination of fatigue damage at poly-frequency loading L1--n by the data of single-frequencyloading L1 can be presented in the following form:

L1−n = L1

1 + ∑

i = 2

n

(κi -- 1)

. (12)

By analogy with dependence (9) the coefficient oflowering of cyclic fatigue life at polyfrequency loadingcan be found from expression (12) in the followingform:

12/2008 27

κ1-2 = 1 + ∑ i = 2

n

(κi -- 1). (13)

This dependence allows determination of cyclic fa-tigue life at polyfrequency loading N1--n similar to (2)by the following formula:

N1−n = N1/

1 + ∑

i = 2

n

(κi -- 1)

. (14)

At practical application of expressions (13) and(14) it is important to correctly select the procedureof determination of values κi for individual compo-nents by expression (1). Two approaches can actuallybe applied: first is to determine value κi relative to acommon basic component, which has the largest am-plitude of σa1 stresses, i.e. κ2, 1; κ3, 1; κ4, 1, etc., andthe second is to determine κi value by the ratio ofparameters between individual components in the se-quence of lowering of σai stress amplitudes, i.e. κ2, 1;κ3, 2; κ4, 3, etc.

It is seen from Figure 1 that the greatest changeof cycle shape of the basic component (a1, b1) is causedby the component second by its level and frequency.The third component has the greatest influence on thecycle shape of the second component, etc. Proceedingfrom that it may be assumed that at a small numberof components there will be no essential differencesin finding κ1--n with both variants of κi determination.However, at a great number of the components, thesecond variant will be a preferable, and, therefore, amore general solution.

The final conclusion about the adequacy of theproposed method and selection of the respective vari-ant of determination of κi coefficients can be derivedbased on the results of experimental verification. With

this purpose, flat samples (Figure 2) with a centralhole, as well as those with a butt welded joint, weremade and tested for fatigue at single- and polyfre-quency soft axial tension. As noted above, at polyfre-quency loading the individual components can differessentially by frequency, and fatigue resistance ofwelded joints can depend not only on the interrelationof the component parameters, but also on the nominalvalues of frequencies. Considering that the degree ofthe influence of loading frequency on the cyclic lifedecreases noticeably with increase of strength prop-erties of structural materials [6], in order to eliminateor markedly lower the influence of this factor on test-ing results, the samples were made of high-strengthsteel with the yield limit of about 1000 MPa. To deriveinitial data under the conditions of zero-to-tensionsingle-frequency loading, fatigue testing of base metalsamples was performed at the frequencies of 3, 30 and300 cycles per minute, included into the frequencyrange, in which the greatest change of fatigue resis-tance is usually observed, and which covers the fre-quencies of the main alternating loads of many weldedmetal structures. At polyfrequency loading the spec-trum consisted of several components of different fre-quency and amplitude. In the real structures, the levelsof higher frequency components are lower than thoseof the basic alternating load, and they usually decreasewith increase of the nominal frequency, while thephase shift between them can change arbitrarily intime. Modes of sample testing at polyharmonic loadingwere assigned in a similar fashion. Ratios of stressamplitudes of three-frequency loading σa1:σa2:σa3 wereset in the ranges close to 1:0.4:0.2, and ratios of fre-quencies f1:f2:f3 ---- in the ranges of 1:3:9 and 1:9:81with zero initial phase of the basic component, andinitial phase ϕ = π of the other components unfixedduring testing. Part of samples with the number ofcomponents equal to 4--7 was tested in a similar fash-ion. Asymmetry and number of cycles at polyharmonicloading were determined by the basic component, hav-ing the lowest frequency and highest amplitude. Theinitial stage of crack propagation was taken as thecriterion of fatigue fracture of these samples. Duringtesting the fatigue cracks usually initiated on the innersurfaces of the hole located on the sample horizontalaxis, and propagated along the length and depth nor-mal to the applied load. At fatigue cracks coming tothe sample side surface and reaching the length of upto 3--4 mm, testing was interrupted. Results of fatiguetesting of base metal samples from high-strength steelat single-frequency loading are presented in thegraphic form in Figure 3, curve 1, and at polyharmonicloading ---- in the Table.

Taken as the main kind of welded joint, was a buttweld which is widely accepted in load-carrying struc-tural elements, and has a high fatigue resistance underalternating loading conditions. Dimensions of weldedsamples (see Figure 2, b) were selected from the con-dition of the possibility of development of high resid-

Figure 2. Schematics of samples for fatigue testing at single- andpolyfrequency loading from base metal with a central hole (a) andwith a butt welded joint (b)

28 12/2008

Results of fatigue testing of samples of base metal and welded joints of high-strength steel at polyharmonic axial tension (r = 0, ϑ == 1.67)

Samples

Sample loading mode

Frequency, Hz Stresses, MPa

f1 f2 f3 f4 f5 f6 f7 σa1 σa2 σa3

Base metal 1.62 4.86 14.58 -- -- -- -- 210 84 43

0.54 1.62 4.86 -- -- -- -- 210 83 84

0.18 1.62 14.58 -- -- -- -- 189 70 25

0.18 1.62 14.58 -- -- -- -- 198 80 41

0.06 0.54 4.86 -- -- -- -- 195 76 40

0.02 0.18 1.62 14.58 -- -- -- 203 77 61

0.02 0.06 0.18 1.62 14.58 -- -- 219 93 65

0.02 0.06 0.18 0.54 1.62 14.58 -- 213 88 62

0.02 0.06 0.18 0.54 1.62 4.86 14.58 225 67 56

Butt joints 0.54 1.62 4.86 -- -- -- -- 154 63 30

0.54 1.62 4.86 -- -- -- -- 141 56 29

0.54 1.62 4.86 -- -- -- -- 132 52 27

0.54 1.62 4.86 -- -- -- -- 95 28 15

0.18 1.62 14.58 -- -- -- -- 84 34 17

0.18 1.62 14.58 -- -- -- -- 123 50 25

0.18 1.62 14.58 -- -- -- -- 140 42 21

0.18 1.62 14.58 -- -- -- -- 158 48 24

0.02 0.06 0.18 1.62 14.58 -- -- 100 41 30

0.02 0.18 0.54 1.62 4.86 14.58 -- 100 38 35

0.02 0.06 0.18 0.54 1.62 4.86 14.58 120 48 42

Table (cont.)

Samples

Sample loading modeCycle number, thou

Coefficient κ

Stresses, MPa Exp. Calculation

σa4 σa5 σa6 σa7Polyharmo-

nicSingle-

frequencyκexp

Variant 1κc1

Variant 2κc2

Base metal -- -- -- -- 25.0 91 3.6 3.20 3.64

-- -- -- -- 14.0 91 6.5 5.41 7.56

-- -- -- -- 20.0 115 5.3 5.48 6.51

-- -- -- -- 14.1 110 7.8 7.98 9.97

-- -- -- -- 6.9 105 15.2 7.69 10.08

39 -- -- -- 2.6 96 36.9 19.22 30.83

46 23 -- -- 3.61 75 20.8 10.00 22.47

43 32 18 -- 2.07 80 38.6 9.63 17.14

46 31 22 11 2.74 66 24.1 9.21 15.50

Butt joints -- -- -- -- 7.0 32 4.5 3.16 3.51

-- -- -- -- 5.0 44 8.8 3.20 3.66

-- -- -- -- 12.0 60 5.0 3.18 3.65

-- -- -- -- 30.0 80 2.7 2.50 3.39

-- -- -- -- 44.4 250 5.6 7.83 9.68

-- -- -- -- 6.0 70 11.7 7.89 9.71

-- -- -- -- 11.9 44 4.7 5.01 8.27

-- -- -- -- 4.5 28 6.2 5.10 8.31

15 5 -- -- 7.65 60 7.8 6.87 12.60

29 20 10 -- 2.6 60 23.0 24.56 16.10

40 30 24 12 1.03 30 29.0 22.49 18.60

12/2008 29

ual stresses in them during welding and inducing therequired working stresses at fatigue testing in theSCHENCK servohydraulic machine of PC1 type withthe force of 1000 kN. Samples were made from sheethigh-strength steel of 20 mm thickness. Sample blankswere cut along the rolling direction using Kiev-4 typemachine for air-plasma cutting of metal. Plate surfaceswere treated by milling with subsequent grinding ofthe working part to the thickness of 10 mm. Two-sidedsymmetrical edge preparation was performed at theangle of 45° with 2 mm toe. Sample welding wasconducted by DCRP mechanized process. Sv-03GKhN3MD electrode wire of 3 mm diameter andFIMS-20P flux were used as welding consumables.To ensure a high cracking resistance of the metal ofthe weld and HAZ, sample edges to be joined werepreheated to 373 K before welding. Each sample waswelded separately in four passes in the horizontal po-sition, and the start and end of the butt weld werelocated on run-off tabs, welded to the plates beforewelding. After welding, the run-off tabs were removedby air-plasma cutting, and the side faces were milled.

As the rational use of high-strength steels in weldedstructures is achieved at asymmetrical axial tension,the characteristic of the cycle of single-frequency andbasic component of polyfrequency loading was takento be equal to r = 0.3. A fatigue crack 3 mm long onthe sample surface was taken as the criterion for com-pletion of fatigue testing. Fatigue testing of weldedsamples at single-frequency loading was conductedunder the conditions of soft harmonic axial tension at3 Hz frequency. Fatigue cracks initiated in the samplesalong the line of fusion of the weld with the basemetal. Results of fatigue testing of welded samples atsingle-frequency loading are given in Figure 3,curve 2. Testing modes of welded joints at polyhar-monic loading were selected similar to those for basemetal samples with three, five, six and seven compo-nents (Table). Calculated values of total coefficientsof lowering of cyclic fatigue life of base metal andwelded joint samples at polyharmonic loading, deter-mined by the first κc1 and second κc2 variants are alsoshown in the Table. Results of comparison of calcu-

lated κc coefficients of fatigue life lowering with ex-perimental values κexp given in Figure 4, show thatboth the calculation variants yield an acceptable ac-curacy at polyharmonic loading with 3 to 7 compo-nents. However, the second variant of calculation κc2is preferable, as it provides a certain fatigue life marginat loading with 3 to 5 components. It should be notedthat the results of κc/κexp comparison have an in-creased scatter at first glance. However, in this caseit is, probably, difficult to obtain a higher accuracyof experimental κexp and calculated κc values. This isrelated to a change of the value and nature of thetotal load cycles, which at low frequency ratios dependnot only on the amplitude ratios, but also on the lawof the change of phase shift between the components.During loading this regularity is determined by theinitial phase shift, as well as the relationship and orderof the component frequencies. It is impossible to in-fluence the nature of this dependence under the actualconditions of structure operation. Therefore, the sug-gested analytical dependencies use formula (1), notallowing for the phase shift between the componentsand applied at bifrequency loading with frequencyratio of not more than 10, when the phase shift impactcan be neglected. However, at aliquant frequency ra-tios, the phase shift between the components, and,accordingly, the nature and value of the summary loadchange continuously in time from the minimum tomaximum values. In these cases, the effective summaryload will, probably, be its value average over the timeof impact. At multiple ratios of frequencies and fixedphase shifts between the components (see Figure 1),maximum or minimum κexp values can be obtained,depending on their initial values. In building metalstructures the latter cases are improbable, and underthe conditions of fatigue testing in modern equipmentwith program control, they are quite feasible.

CONCLUSIONS

1. Proposed procedure and analytical dependences al-low determination of the coefficients of lowering of

Figure 4. Results of comparison of calculated κc and experimentalκexp values of the coefficients of lowering of cyclic fatigue life forsamples of base metal (BM) and butt welded joint (BWJ) at poly-harmonic loading: 1 ---- first variant of calculation of BM (l) andBWJ (n), respectively; 2 ---- second variant of calculation of BM(s) and BWJ (u), respectively

Figure 3. S--N curves of samples from high-strength steel with acentral hole (1) and with a butt welded joint (2) at single-frequencyaxial tension: ∆, r, m ---- r = 0, respectively f = 3, 30, 300 min--1;l ---- r = 0.3, f = 180 min--1

30 12/2008

cyclic life of materials and welded joints at polyfre-quency loading.

2. Proceeding from the initial data of single-fre-quency loading and assigned parameters of polyfre-quency loading components, it is possible to predictthe cyclic fatigue life of metal structure elements underthese conditions.

3. Data of experimental studies of cyclic life ofsteel base metal and butt welded joints derived in thiswork, confirmed the acceptable accuracy of the pro-cedure and calculated dependencies. At 3 to 7 com-ponents of polyharmonic loading the main part of theresults of comparison of the calculated and experi-mental values of the coefficient of cyclic life loweringis in agreement with a not more than 40 % error.

1. Buglov, E.G., Filatov, M.Ya., Kolikov, E.A. (1973) Resis-tance of materials at bifrequency loading (Review). Proble-my Prochnosti, 5, 13--17.

2. Trufyakov, V.I., Kovalchuk, V.S. (1982) Determination offatigue life at bifrequency loading. Report 1: Review. Ibid.,9, 9--15.

3. Geminov, V.N. (1967) About physical principles of the me-thods of damage summation under nonstationary loadingconditions (Review). In: Strength of materials at cyclicloads. Moscow: Nauka.

4. Troshchenko, V.T., Sosnovsky, L.A. (1987) Fatigue resis-tance of metals and alloys: Refer. Book. Pt 1. Kiev: Nau-kova Dumka.

5. Trufyakov, V.I., Kovalchuk, V.S. (1982) Determination offatigue life at bifrequency loading. Report 2: Proposed pro-cedure. Problemy Prochnosti, 10, 15--20.

6. Kovalchuk, V.S. (1991) Influence of loading frequency onfatigue resistance of steels and welded joints. Avtomatich.Svarka, 1, 30--34.

IMPROVEMENT OF TRIBOTECHNICALCHARACTERISTICS OF HARDFACED CAST IRON

AUTOMOBILE CRANKSHAFTS

S.Yu. KRIVCHIKOVE.O. Paton Electric Welding Institute, NASU, Kiev, Ukraine

Influence of heat treatment modes on tribotechnical characteristics of working mating arrangements of hardfaced crank-shafts operating under conditions of metal against metal friction with lubrication was assessed. It is shown that temperingtemperature influences quantitative ratio between pearlite and carbide-cementite phases in structure of the depositedmetal and its wear resistance.

K e y w o r d s : arc surfacing, deposited metal, structure andhardness, tribotechnical characteristics, heat treatment

A crankshaft is the most loaded part of the internalcombustion engine (ICE). Main loads, which deter-mine its service life, are high contact pressure in rub-bing mating arrangements and big number of alter-nating load cycles. This causes irregular wear andmisalignment of working surfaces, violation of oilfilm, and creation of conditions for dry and marginalfriction. As a result «seizure» and melt-out of inserts,mated with hardfaced crankshaft journals, may occur.

In repair production technology of wide-layer sur-facing using the PP-AN160 self-shielded flux-coredwire is widely used for renovation of worn cast ironICE crankshafts [1]. The deposited metal representsa wear-resistant high-carbon alloy, the crankshaft basemetal is cast iron of the VCh 50-2 grade (ChShG)hardened for pearlite structure. Chemical composi-

tions of the base and the deposited metal are given inTable 1.

Experience of operation and repair of the hardfacedcrankshafts shows that wear resistance of the hard-faced journals exceeds that of the base metal, but wearof the mated with the hardfaced journal insert occursmore intensively than of the deposited metal.

Purpose of this work is experimental investigationof influence of the deposited metal heat treatment ontribotechnical characteristics of working mated ar-rangements of crankshafts.

Testing of friction--sliding pairs with a lubricationwas performed on the SMT-1 friction machine accord-ing to the «roller--block» scheme in agreement withGOST 23224--86. Segments from standard automobileAO 20-1 inserts were used as the blocks. For manu-facturing of the rollers (Figure 1) billets from ChShGwere used, cylindrical surface of which was hardfacedusing the PP-AN160 flux-cored wire, then they were

© S.Yu. KRIVCHIKOV, 2008

Table 1. Chemical composition of deposited and base metal, wt.%

Alloy investigated C Cr Si Mn Ti Al B Mg

Deposited metal 2.4 0.3 1.8 0.8 0.3 0.5 0.08 --

Base metal (ChShG) 2.8 0.2 2.1 1.3 -- -- -- 0.03

12/2008 31

subjected to heat treatment and grinding up to nomi-nal dimensions. Heat treatment was performed underfollowing conditions: heating in the furnace up to theassigned temperature, soaking at this temperature for2 h, and cooling in quite air.

Testing of friction pairs was performed in twostages: under conditions of alignment of mating partsand at the working load. Optimum working load Popwas chosen on basis of preliminary experiments whichshowed that its excess could cause «seizure» of themating arrangements. Total intensity of wear of themating arrangements as a whole IΣ was determined astotal of intensity of wear of the insert Ii and the rollerIr (methodology for determining these values is givenin GOST 23.224--86). In addition, in the process ofthe tests recording of the friction factor change ffr(Figure 2) and temperature of the oil friction heatingTfr was performed. The results obtained (Table 2)prove that heat treatment exerts significant influenceon tribotechnical characteristics of both depositedmetal and the insert and the mating arrangement asa hole. One may see from comparison of intensities ofwear of mating arrangements 1 and 2 that wear resis-tance of the deposited metal exceeds that of the basemetal, but intensity of the insert wear Ii in matingarrangement 2 is 2.2 times higher than in mating ar-rangement 1. According to other indices of wear re-sistance and serviceability the ChShG--insert frictionpair also exceeds the deposited metal--insert matingarrangement.

After heat treatment at Ttemp = 400--420 °C tri-botechnical properties of mating arrangement 2 insig-

nificantly improve: values Ii, IΣ, ffr and Tfr reduce,and Pop increases. By means of Ttemp increase up to520--550 °C listed parameters undergo significantchanges and achieve values at which mating arrange-ment 2 in all tribotechnical parameters exceeds matingarrangement 1. Further increase of Ttemp causes sig-nificant worsening of the deposited metal wear resis-tance and serviceability of the mating arrangement asa whole.

For determining reasons of change of tribotechni-cal characteristics of mating arrangements at heattreatment of the deposited metal the metallographicinvestigations were carried out. It should be notedthat detailed analysis of structural-phase state of themulticomponent alloy, solidification of which oc-curred under non-equilibrium conditions, is a ratherlabor-consuming task. However, it was establishedwith sufficient degree of accuracy that structure ofthe deposited metal consisted of two main phases:products of austenite decomposition (pearlite + resid-ual austenite) and carbide-cementite phase. The latterin plane of the section had an appearance of a branchedreinforcing mesh with areas of different thickness. InFigure 3 this phase has white color, while pearlite-austenite phase has dark color which made it possibleto evaluate their quantitative ratios.

Figure 2. Change of friction factor upon time of aligning of thebase metal--insert (1) and deposited metal--insert (2) mating ar-rangement after heat treatment at Ttemp = 520--550 °C (2) at vsl == 0.8 m/s

Table 2. Tribotechnical characteristics of friction--sliding pairs

Matingarrangement

Type of matingIndices of serviceability Intensity of wear, mm/m⋅10--4

ffr⋅10--2

Pop, MPa Òfr, îÑ Ir Ii IΣ

1 Base metal ChShG--insert 16.0 60 0.29 0.12 0.41 35

2 Deposited metal--insert

without heat treatment 11.0 72 0.24 0.26 0.50 45

after heat treatment at T, °C:

400--420 11.6 68 0.24 0.24 0.48 42

520--550 14.0 50 0.22 0.12 0.34 20

650--700 9.5 80 0.49 0.10 0.59 68

Figure 1. Roller for determining tribotechnical characteristics offriction--sliding pairs: external diameter of 50 mm, thickness of12 mm

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It was established that by means of increase of thetempering temperature carbide-cementite mesh firstgets thinner, then gets torn, and, at last, disintegratesinto separate inclusions of cementite. In initial state(without heat treatment) the deposited metal contains40--46 % of «white» (carbide-cementite) phase ofhardness HV0.5-8000--8200 MPa. MicrohardnessHV0.5 of the solid solution grains («dark phase») is5800--6200 MPa. As a result of heat treatment at tem-peratures 520--550, 650--700 and 800 °C the share ofcarbide-cementite phase constituted 28--33, 21--25 and8--12 % respectively, and its hardness remained un-changed.

By means of increase of Ttemp microhardness ofpearlite monotonously diminished from HV0.5-5200--

5400 (at Ttemp = 400 °C) to HV0.5-4200--4400 (atTtemp = 800 °C) which is connected with a partialdecomposition of secondary cementite into iron andgraphite at heating [2]. Influence of tempering tem-perature on hardness of the deposited metal is pre-sented in Figure 4. Reduction of hardness by meansof temperature increase is, evidently, stipulated byreduction of the solid carbide-cementite phase sharein the deposited metal.

So, on basis of the results obtained one may statethat tribotechnical characteristics of mating arrange-ment 2 may be improved by means of heat treatmentof the deposited metal at Ttemp = 520--550 °C. Increaseor reduction of the temperature is accompanied byworsening of the friction pair serviceability parame-ters, whereby maximum wear resistance of both thedeposited metal and a mated with it insert is ensuredby achievement of optimum quantitative ratio betweentwo main phases of its structure.

1. Krivchikov, S.Yu., Zhudra, A.P., Petrov, V.V. (1994) Cur-rent technologies of arc hardfacing of crankshafts. Svarochn.Proizvodstvo, 5, 4--6.

2. Zhudra, A.P., Krivchikov, S.Yu., Petrov, V.V. (2006) Ef-fect of silicon on properties of low-alloy carbon depositedmetal. The Paton Welding J., 8, 43--44.

Figure 4. Influence of tempering temperature on hardness of de-posited metal

Figure 3. Influence of heat treatment on structure of depositedmetal: a ---- without heat treatment; b--d ---- at Ttemp = 400--420,520--550 and 700--750 °C, respectively (×320)

12/2008 33

ON ISSUE OF BRAZING METALS USING POWDERBRAZE ALLOYS OF DIFFERENT DISPERSITY

A.S. PISMENNY, V.I. SHVETS, V.S. KUCHUK-YATSENKO and V.M. KISLITSYNE.O. Paton Electric Welding Institute, NASU, Kiev, Ukraine

The paper presents results of investigations of copper and brass joints made using silver powder with less than 1 µmparticle size as the braze alloy. Explanation is given of abnormally high formation rate of the seam melt of eutecticcomposition in brazing. Application of powders with higher degree of dispersity has good prospects for joining structuralmaterials for which heating temperature is critical.

K e y w o r d s : brazing, powder braze alloy, silver, dispersity,brazing temperature, process activation

At present new composite despersion-strengthenedand other metal-base materials are used insufficientlywidely because of absence of reliable methods for theirjoining. Because of this reason development of thejoining methods which would not be inferior to theexisting ones in respect to productivity and quality isan actual issue.

In application of welding or high-temperaturebrazing processes an important and not completelysolved issue is loss of strength of the materials beingjoined in the heat-affected zone.

One of efficient methods of reducing brazing tem-perature became application as filler materials ofamorphous films and nanolayer foils which, as it isknown, interact more actively in comparison with tra-ditional braze alloys [1, 2] with the base metal.

In a number of works reduction of the meltingpoint of the materials, dispersed down to the nanosizelevel, is noted [3, 4]. Of interest is application of thisphenomenon for reduction of the brazing temperature.Up till now investigations in these directions werenot carried out which was, evidently, connected withinstability of properties of fine-dispersed metal pow-ders.

The goal of this work consisted in technologicalcheck of possibility of reducing of the copper and brassbrazing temperature due to dispersity increase of thepowder braze alloy.

It is known that in brazing of copper and brassusing silver due to contact melting a molten phase isformed which plays part of the braze alloy. Its com-position corresponds to composition of eutectics of theCu--Ag system with melting point 779 °C [5]. In con-tact melting of brass and silver the eutectic phase ofthe Cu--Ag--Zn triple system is formed which has melt-ing point below 700 °C [6]. For intensification ofdiffusion interaction of the contacting metals the braz-ing temperature should exceed melting point of theeutectics.

In the experiments copper of the M1 grade, brassof the LS68 grade, and silver of commercial puritywere used. A monodispersed silver powder with par-ticles less than 1 µm was produced under laboratoryconditions by means of anode dissolution, and morecourse fraction ---- by mechanical comminuting.

The experiment was carried out as follows: on pe-ripheral areas of the copper substrate shots of silverpowder with size of the particles less than 1 µm, andon central areas ---- more than 100 µm ---- were applied(Figure 1). Silver powder was used in mixture withthe F284 flux. Silver powder shots were arranged be-tween mica plates at distance 0.5 mm from each other.

Heating was performed using hydrogen-oxygenflame in center of the copper substrate from its lowerside. Presence on the copper substrate of dividinggrooves of up to 3 mm depth allowed creating tem-perature field from center to periphery of the substratewith the gradient not less than 50 deg/mm. So, coursefraction powders were subjected to heating up to thetemperature which was by more than 50 °C higherthan temperature of the powder shots with particlesizes less than 1 µm.

Process of the silver powder melting in heatingwas controlled using the MBS-2 optical microscope(magnification power equals 32).

The experiments showed that in heating after melt-ing of the flux first formation of the molten metalphase on the contact boundary of the copper substrate

Figure 1. Scheme of copper substrate heating: 1 ---- spacers frommica plates; 2 ---- copper substrate; 3, 4 ---- silver powder with sizeof particles respectively less than 1 µm and more than 100 µm inmixture with F284 braze flux

© A.S. PISMENNY, V.I. SHVETS, V.S. KUCHUK-YATSENKO and V.M. KISLITSYN, 2008

34 12/2008

with the silver powder, which had size of the particlesless than 1 µm, occurred. On contact boundary withcoarser silver particles the molten metal phase isformed in significant volumes only at heating to ahigher temperature. Time delay of the contact meltingof the powder with a coarser fraction equals about5 s. According to readings of the thermocouples, atthe time of melting of the powder with a coarser frac-tion temperature in this area is by more than 50 °Chigher than temperature of the area with silver powderof finer fraction.

In our opinion intensification of the contact melt-ing in case of comminution of silver particles is stipu-lated by significant increase of the silver powder con-tact surface ---- main component of the melting process.In addition to increase of the contact surface area withthe copper substrate, bringing of silver to the contactboundary occurs due to diffusion and mass transfer inthe flux melt. Probably, in this case more complexprocesses occur that require for further investigations.As a version one may assume that reduction of thesilver melting point occurs due to comminution of itsparticles down to the size less than 1 µm.

Possibility of practical implementation of the ob-served effect was checked in brazing of specimens fromcopper and brass. On specimens of 30 × 5 × 0.3 mmsize a braze alloy material was applied, which repre-sented mixture of the F284 flux and silver with sizeof particles less than 1 µm. The specimens were lapped,compressed between two rods from ceramics usingforce up to 3 N, and subjected to heating by a hydro-gen-oxygen flame.

It was established that formation of the joints atheating within approximately 30 s occurred at the tem-perature close to the eutectic one, while at brazing usingtraditional braze alloys of the Ag--Cu system, for exam-ple a standard PSr72 braze alloy, it was necessary toheat specimens up to the temperature, which was bymore than 50 °C higher than the eutectic one [6].

Investigation of the microstructure and chemicalinhomogeneity of brazed joints of the specimens frombrass and copper, produced with application of silverpowder with particles of less than 1 µm size, werecarried out using the optical microscope «Neophot-32»and the Camebax microanalyzer SX-50.

Microstructure analysis of joints of specimens frombrass (Figure 2) showed that phase transformationsdid not occur in HAZ. Metal of the brazed seam hada homogeneous fine-dispersed structure, and proceed-ing from distribution of the elements (Figure 3) rep-resented an alloy of eutectic composition of the Cu--Ag--Zn system. Width of the brass diffusion zone wasabout 15 µm.

Distribution of copper and silver in copper joints(Figure 4) also proved formation in a brazed seam ofa fine-dispersed alloy of eutectic composition. Thediffusion zone width of silver in copper did not exceed7 µm.

Comparative tensile tests of specimens from copperand brass, brazed using silver powder with size ofparticles less than 1 µm and the PSr72 braze alloy,showed that mechanical properties of produced jointswere practically identical.

CONCLUSIONS

1. Application of silver powders with size of particlesless than 1 µm allows reducing temperature of con-tact-reactive brazing of copper and brass not less than

Figure 4. Ditribution of copper and silver in joint of specimensfrom copper brazed using silver powder with size of particles lessthan 1 µm (length of area ---- 80 µm; step ---- 10.1 µm)

Figure 2. Joint microstructure of specimens from brass brazed usingsilver powder with particles of less than 1 µm size (×100)

Figure 3. Distribution of silver, zinc (a) and copper (b) in jointof specimens from brass brazed using silver powder with size ofparticles less than 1 µm (length of area ---- 750 µm; step ---- 49.7 µm)

12/2008 35

by 50 °C, as well as time of the braze alloy meltformation.

2. Activation of the melting process at increase ofthe powder braze alloy dispersity is stipulated by in-crease of the silver powder surface as the main com-ponent of the contact melting process and intensifi-cation of mass transfer in the flux melt.

3. Application of powders with high degree of dis-persity as the braze alloy materials has good prospectsfor joining thermally unstable structural materials.

1. Ishchenko, A.Ya., Falchenko, Yu.V., Ustinov, A.I. et al.(2007) Diffusion welding of finely-dispersed AMg5/27 %

Al2O3 composite with application of nanolayered Ni/Al foil.The Paton Welding J., 7, 2--5.

2. Kuchuk-Yatsenko, V.S., Shvets, V.I., Chvertko, P.N. et al.(2004) Flash-butt welding of dispersion-hardened copperalloy of Cu--Al2O3 system. Ibid., 11, 2--4.

3. Bogdanov, K.Yu. (2008) Why nanoparticles melt at lowtemperatures? http:www.nanometer.ru/2008/02/9/nanjc-hastici_temperature_plavlenia_60-57.html

4. Zhang, M., Efremov, M.Yu., Schiettekatte, F. et al. (2000)Size-dependent melting point depression of nanostructures:nanocalorimetric measurements. Phys. Rev. B, 62(15), Oct.,10548--10557.

5. Khryapin, V.E. (1981) Reference book of tinman. Moscow:Mashinostroenie.

6. (1984) Reference book on soldering. Ed. by I.E. Petrunin.Moscow: Mashinostroenie.

THESES FOR A SCIENTIFIC DEGREE

E.O. Paton Electric Welding Institute, the NAS ofUkraine

A.S. Milenin (PWI) defended on 8 of October 2008candidate’s thesis on topic «Kinetics of ther-momechanical processes in braze-welding of titanium-aluminium beam structures».

The thesis was devoted to investigation of charac-teristic peculiarities of kinetics of thermomechanicalstate of titanium-aluminium beam structures in proc-ess of their braze-welding for the case of developmentand optimization of the production cycle of dissimilarstructural elements of aviation designation (guides ofarmchairs). On basis of results of numerical and ex-perimental investigations influence of technologicalparameters of the braze-welding process was deter-mined on peculiarities of formation of stress fields inthe area of dissimilar contact and on strained state ofa beam structure after welding. Character of changeof residual stress-strain state of dissimilar structuresafter heat treatment and machining of different kindswas determined.

Methodology for assessing risk of formation of in-termetallic compounds in the area of the surface con-tact of molten aluminium with solid titanium wasfurther developed. Physical explanation of the proc-esses at initial stage of the braze-welding contact for-mation was made. Universal methodology for assess-

ing risk of formation of embrittlement intermetallicinclusions as a result of reaction diffusion in variableand inhomogeneous temperature field in the area ofthe surface contact of titanium with aluminium wasdeveloped. This allowed determining character of in-fluence of the welding heat source on risk of formationof this kind of defects in case of braze-welding of thetitanium-aluminium beam aviation structures.

Peculiarities of the metal plastic strain kinetics inthe process of braze-welding of structures from tita-nium and aluminium from the viewpoint of risk of thehot crack formation in aluminium part of the dissimilarjoint were detected. Increased risk of the cross hotcrack formation in the weld metal of a dissimilar braze-welded joint was demonstrated.

For efficient analysis of the numeric investigationresults the computer means for modeling ther-momechanical processes in braze-welding and post-weld treatment of titanium-aluminium beam struc-tures were included into the problem-oriented soft-ware package.

Complex of investigations for determining inputparameters of the developed models was carried out,which allowed obtaining efficient means for computermodeling of thermomechanical processes in dissimilaritems. The data, obtained using modeling experiments,correlate with high accuracy with results of respectivenumeric investigations.

On basis of numeric analysis of results of ther-momechanical processes in braze-welding and post-weld treatment of titanium-aluminium guides of arm-chairs were determined optimum technological pa-rameters of these production cycles. Numeric investi-gations of influence of variation of the braze-weldeddouble tee beam structure geometric parameters, inparticular position of the dissimilar butt joint, on re-sidual strains of the item bend allowed determiningoptimum ratio of titanium and aluminium parts of thedouble tee profile wall. Developed methodologies forassessing risk of forming defects of a dissimilar struc-ture made it possible to specify allowable ranges ofvariation of the welding technological parameters

36 12/2008

from the viewpoint of minimization of the risk of oc-currence of embrittlement intermetallic layers and hotcracks.

Influence of postweld treatment of different kinds(local and general heat treatment, mechanical dress-ing) on residual stresses in the dissimilar contact area

and shape of a dissimilar beam structure was investi-gated. Optimum technological parameters of theseprocesses were determined.

On basis of results of the carried out investigationsscientifically substantiated additions to technologicalrecommendations were developed.

A.S. Zatserkovny (PWI) defended on 8 of October2008 candidate’s thesis on topic «Modeling of heatexchange processes of low-temperature plasma jetwith evaporating and exothermally reacting particlesof a disperse material».

The thesis is devoted to theoretical investigationand mathematical modeling of thermal and dynamicinteraction of the plasma jet with particles of thedisperse materials under conditions of the plasmaspraying of coatings. Theoretical models for calculat-ing heat exchange of a particle being sprayed withmulticomponent plasma by accounting for energy in-put of ion and electron heat flows and exothermalreaction between the composite particle componentswere suggested.

On basis of analysis of physical processes, proceed-ing in Knudsen plasma layer near surface of the par-ticle being sprayed, analytical expressions for calcu-lating densities of electron and ion currents fromplasma on surface of a particle, the potential fall be-

tween the plasma and the particle, and electron andion components of heat flow from the plasma into theparticle, were obtained. Method for determining pa-rameters of such plasma on external boundary ofKnudsen layer, which enter into the obtained analyti-cal expressions, was determined. Within wide rangeof temperature change of the undisturbed argonplasma and the aluminium particle surface tempera-ture the numeric analysis of composition, temperatureof electrons, and heavy component of the near-surfaceplasma was carried out, and respective values of heatflows into the particle were calculated.

Mathematical model of heat processes, which pro-ceed in a composite particle at its heating in the plasmajet, taking into account exothermal reaction of theintermetallic compound synthesis within its volume,was developed.

Calculation algorithms were found and respectivesoftware was developed using which a detailed com-puter modeling was carried out of movement and heat-ing of both homogeneous (metal) evaporating andcomposite exothermally reacting particles in theplasma jet.

For the purpose of verification of the suggestedmathematical models a series of full-scale experimentsin spraying of Ni--Al composite powder were carriedout. Using obtained experimental data parameters ofthe model of the composite particle movement weredetermined, and parameter, which characterizes rateof the exothermal reaction progress in their volume,was calculated. Suggested mathematical models ofmovement and heating may be adapted for wide rangeof the plasma spraying parameters and composite pow-ders of different composition and structure.

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A.A. Pismenny (PWI) defended on 22 of October2008 candidate’s thesis on topic «Efficiency increaseof power supply of machines for resistance spot weld-ing».

The thesis is devoted to analysis of the power sup-ply and control problems of machines for resistancespot welding (RSW). On basis of analysis the mostpromising directions for further works in this fieldwere determined. The thesis contains systematizedanalysis of known power supply systems for RSW onbasis of which were carried out theoretical and calcu-lation assessments of the most promising systems.

High efficiency of the reactive power longitudinalcompensation systems of single phase machines forRSW of low and medium power up to 1000 kV⋅A wasproved. In comparison with conventional single-phasemachines they have significantly higher power factor,ensure increased stability of electrodes and stabilityof quality of the joints within wide range of theirspecific resistances.

Methodology for calculating power factors andvalues of relative voltages and currents on basis ofassigned values of the angle for switching-on thethyristor contactor at various values of active resis-tance of the load was developed. It was establishedusing the new developed method of calculation thatwithin the range of the thyristor switch-on angles up

to 60 electrical degrees one may obtain high values ofpower factor cos ϕ (up to 0.95), deviation from fullcompensation in direction of under-compensation be-ing 25 %.

Power supply system with a three-phase converterof the number of phases and 30 Hz frequency wasrecognized a promising one for the RSW machines ofmore than 100 kV⋅A power. Quasi-symmetrical workof the converter allows achieving close to uniformdistribution of current over the network phases with-out loading of zero wire, while reduction of the work-ing current frequency allows increasing the machinepower factor cos ϕ by 20--30 % in comparison withtraditional power supply system of the RSW machinesof industrial frequency. In technological relation ap-plication of AC welding at reduced 30 Hz frequencywill allow increasing acting value of current underload and reducing risk of partial melting of the weld-ing electrodes and cases of the metal splashing outfrom the welding zone.

It was suggested to use for welding and micro-welding of parts of small (less than 1 mm) and espe-cially small (below 0.1 mm) thicknesses an inverterconverter of increased frequency of welding currentas alternative of the capacitor-type welding.

The work contains description of the developeddesign, manufacturing and testing of the experimentalmodel of the inverter power supply source of increasedcurrent frequency 500 Hz for resistance spot microw-elding in which a specially developed algorithm forautomatic control of welding conditions is imple-mented. This power supply source ensures process ofhigh-quality welding of items within thickness range0.05--0.50 mm and simulates power supply source withthe current frequency 30 Hz for welding of itemswithin thickness range 5--8 mm.

New power supply source was successfully testedin welding of the carbon group metals with thicknessof welded parts less than 1 mm. Quality of weldedjoints was positively appraised by leading enterprisesof the country.

38 12/2008

TECHNICAL WORKSHOP OF WELDING SPECIALISTSIN SIMFEROPOL

From 9 till 11 of September 2008 at Electric MachineIndustry Plant of OJSC FIRMA SELMA and its rec-reation grounds «Parus» was held technical workshopof welding specialists on topic «State-of-the-art weld-ing equipment and advanced technology of weldingin ship building, ship repair, crane building and pro-duction of hoisting-transportation equipment». Morethan 30 specialists from enterprises and organizationsof Ukraine (Chernomorsky Ship Building Plant;«Okean»; «Tekhnolazer-svarka» Ltd, Nikolaev;«Cranship»; Ship Repair Plant, Kerch; «Lazurit»;«Avrora» Ltd; FSUE-13, SRP «Yuzhny» Ltd, Sevas-topol; OJSC «Azovmash»; STC «Promavtosvarka»;SRP Ltd, Mariupol; CJSC Crane Building Plant,Nikolaev; the E.O. Paton EWI; «Neftegazstrojizolyat-siya», Kiev; «Zaporozhkran»; OJSC «ZaporozhiePlant of Welding Fluxes and Glass Items»; «Arksel»,Donetsk), 20 specialists from Russia (OJSC«Sevmash», Severodvinsk; Verkhnekamsky ShipBuilding Complex, Perm; «Institute BVIIST» Ltd,Moscow; «ITS»; SE «Admiraltejskie Verfi»; TsNI-ITS, St.-Petersburg; OJSC «Chelyabinsk Pipe-Roll-ing Plant»; «Elektrosvarka», Kaliningrad; «Vineta»Ltd, Nikolskoe) and representative of «DrahtzrugStein Wire Welding», Germany, took part in theworkshop. Managers and chief specialists of main serv-ices of SELMA and ITS also took part in the workshop.

In the assembly hall participants of the workshopwere welcomed by director-general of FIRMASELMA G.V. Pavlenko and director-general of ITSM.V. Karasyov. Technical director S.I. Gritsenko andD.N. Rabochinsky presented brief information.

Then tour of main and support workshops and baysof the plant was made where S.I. Grishchenko andM.V. Karasyov acted as guides.

Success of the enterprise in expansion and upgrad-ing of the production nomenclature, improvement ofmanufacturing technology, application of well organ-ized quality assurance system literally at each workingplace, correctly organized saving regime of the re-sources, incentive system of labor payment, and at-tention paid to social issues made deep impression. Asa result, significant growth of production, expressed,for example, in volumes of the equipment sales, isobserved. It achieved 12--13 mln UAH per month.The plant plans to open Trade house, which will allowactivating marketing activity of the enterprise.

At present SELMA is a dynamically developingenterprise, assortment of equipment of which consti-tutes more than 100 names of welding equipment:welding transformers, rectifiers, semi-automatic ma-chines, welding automatic machines and carryingstructures for mechanization of welding and cutting,

installations for air-plasma cutting, machines for re-sistance spot welding and equipment for controllingspot welding machines, and equipment for mechanicalpreparation of edges for welding. List of producedequipment constantly expands due to development ofnew kinds of welding equipment which meets state-of-the-art requirements of production and applicationof latest achievements of science and technology.

A number of reports were presented at the work-shop within two days. Block of presentations of theSELMA specialists included the following papers:«General review of produced products. New items.Promising directions of the welding equipment devel-opment at SELMA. Welding converters of the KSUtype» (chief designer G.L. Pavlenko); «Welding auto-matic machines for welding and surfacing. Promisingdirections of the equipment development for automat-ic welding at SELMA (V.A. Pankratiev); «Machinesfor mechanical preparation of edges for welding of theMKS and the MKF types» (V.A. Kozarin).

G.L. Pavlenko characterized main kinds of pro-duced by SELMA products, dwelled in detail uponnew developments, for example, the VS-450 rectifier(analogue of Varco star 400), universal sources withchoppers for manual and semi-automatic gas-shieldedand TIG welding, welding converters of the KSUtype, welding automatic machines and automaticheads, structures for automation of welding processes(GK-200 «Proteus» etc.). In future it is planned toproduce automated complexes for air-plasma cutting,equipped with the SELMA sources.

SELMA started production of welding automaticmachines in 1999, having taken as basis automaticmachines of the A2 and A6 type (ESAB). They includethe ADF-1000 and the ADF-1250 automatic machineswith smooth or staged regulation of the welding wirefeeding of 2--5 mm diameter.

12/2008 39

Edge-spalling machines, produced by SELMA, en-sure minimal (close to zero) tolerance in processingof edges and rate of processing more than 2 m/min.They have no disadvantages peculiar for Italian ma-chines (small service life of the reduction gearbox).There is positive experience of using the MKS 214machine at Volzhsky Pipe Plant.

In report of M.V. Karasyov (ITS) activity of thegroup of enterprises, which enter into ITS, was pre-sented. The group includes SELMA company, OJSCESVA (Kaliningrad), «Welding» Ltd. (Lithuania),representative offices and warehouses (Ekaterin-burg ---- ITS-Ural; Krasnoyarsk ---- ITS-SIBIR, ITS-VOLGA; Samara, Moscow ---- ITS MOSCOW, ITS-ENGINEERING, Irkutsk--welding equipment--Irkutsk, etc.), and industrial-warehouse complexPARNAS (St.-Petersburg).

Group of the ITS enterprises annually producesand delivers more than 80 thou units of welding equip-ment in territory of Russia, more than 50 thou unitsin territory of Ukraine, more than 2 thou weldinginstallations are supplied far abroad.

All together volume of production constitutes morethan 149 thou units of welding equipment. Nomen-clature of the items constitutes more than 80 names.Share in CIS among Russian companies constitutes upto 75 % of the whole national welding equipmentoperating in territory of Russia. Share in CIS amongwhole welding equipment of Russian and foreign com-panies is about 50 %.

General number of employees at all ITS enterprisesis 1700. The company has its own recreation grounds«Parus» near Evpatoriya. Production department ofITS in St.-Petersburg specializes in completion on or-der of automated installations for industrial needswith application of standard equipment of SELMAand other companies.

From new kinds of equipment of the ITS enter-prises M.V. Karasyov noted high reliability of welding

converters (choppers), their high efficiency, whichachieves 93 %, and low power consumption. There aregood prospects for their application in ship building.One of advantages of using choppers is achievementof reduced content of hydrogen in the weld metal.Experimental data are available which prove that ap-plication of the converters in composition of the VDU-1500 multipost source (8 converters) in multiarc weld-ing using flux-cored wire allows obtaining fine-grainstructure of the weld metal in welding of pipe steels.According to data of the speaker, application of theKSU-320 converter allows ensuring high efficiency ofits use due to reduction of power consumption, reduc-tion of sputtering in welding, and high technologicalproperties. Among novelties of the equipment, whichare widely used in recent years, the speaker noted theVDU-511 and VD-506DK rectifiers, the installationsfor automatic submerged-arc welding VDU-1500 (di-rect current) and TDFZh-1250 (alternating current).Production of welding complex PROTEUS (TU 3441-028-11143754--2006) deserves attention. It is designedfor automatic gas-shielded or gas mixture-shielded or-bital welding of position joints of pipelines of 406--2540 mm diameter. It includes: two self-propelledwelding heads, a power unit, a guiding belt of 120 mmwidth, a manual programming device (12 programs),a remote control panel, a set of appliances and re-placeable parts, and a welding current source (VD-506DK UZ).

At the workshop presentations of TsNIITS special-ists were also made: N.A. Steshenkova «Developmentof civil ship building within framework of FTsP for2009--2016. Prospects of building of ships of new gen-eration, including gas carriers» and «Innovation tech-nologies of welding suggested for mastering withinframework of FTsP of civil ship building develop-ment»; V.A. Nikitin «Application of robots for weld-ing of ship structures».

The floor was given also to S.V. Golovin (VNIIST)who made report «Quality of welded structures ----the base for increasing reliability, working life andcompetitiveness of ship building»; A.N Alimov (Ark-sel) «Production of seamless flux-cored wires»; A.I.Romantsev (OJSC ChTZ) «New pipe electric weldingworkshop»; R.N. Barannik (Zaporozhie Plant ofWelding Fluxes and Glass Items) «Mastering of pro-duction of new kinds of ceramic fluxes».

Participants of the workshop expressed their grati-tude to representatives of SELMA and ITS for excel-lently organized work of the workshop, its saturatedprogram, and satisfaction with level of presented re-ports.

Prof. V.N. Lipodaev, PWI

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CONFERENCE «BRAZING-2008» IN TOLIATTIOn 10--12 of September 2008 International Conferenceon Brazing was held in Toliatti ---- the highest forumin CIS in this field. Sixty papers from Russia, Ukraineand Germany were presented at the conference.

At plenary meeting great attention was attractedby presentations made by V.S. Novosadov (MoscowUniversity of Food Production) «Phenomenologicaltheory of boundary and diffusion kinetics of solutionin capillary gap»; V.F. Khorunov (E.O. Paton Elec-tric Welding Institute, Kiev) «Brazing of intermetal-lic alloys. Achievements and problems»; V.N. Se-myonov (SPA «Energomash», Khimki) «Model ofphysical-chemical interaction of the EP202 alloy withcopper-silver braze alloy and strength of their bondat interface»; L.S. Lantushenko (OJSC «Kriogen-mash», Balashikha) «Fluxless brazing of aluminiumalloys». These reports generalized results of long-terminvestigations in the field of theory of the metal ma-terial joining, prospects of using intermetallic com-pounds as structural materials, manufacturing of mis-sile engines, achievements in the field of fluxless braz-ing of aluminium alloys.

Interesting information (TSU, Toliatti) containedreports of L.V. Loshkaryov «On possibility of acous-tic-emission control of metals and compounds», andof D.L. Merson «New method of NDT of phisical-me-chanical properties of metals and joints». A pleasantdecoration of the plenary meeting became demonstra-tion of achievements of the jewelry art chair of ToliattiState University.

Doubtless success of the organizers was arrangementwithin the framework of the conference of the seminar«State-of-the-art welding equipment and technology ofwelding and brazing of the Abicor Binzel groups». Sixpresentations were made with subsequent demonstrationof spot plasma welding and manual plasma brazing withapplication of the SBI source and the ABICOR torch;robotized welding and brazing with application of theFANUC robot, the KEMPPI power source and the ABI-COR torch; braze-welding process of galvanized partson the KEMPPI apparatus Pro Evolution. This is a verybright demonstration of close cooperation of Russianspecialists with Western companies.

One more prove of this is significant number (7)of presentations from Germany in addition to thosemade at the seminar. One has to single out from thesepresentations works, carried out under managementof Prof. J. Wilden. So, in paper «New technology forjoining sensitive to heating materials» were presentedresults of investigations of the joints produced withapplication of «cold arc» (cold metal transfer), hybridprocess (cold arc plus laser) in joining, for example,of steels, aluminium with steel, whereby zinc-basealloy was successfully used as a braze alloy. In thework «Nanotechnology and boundary effects as newpossibilities for successful joining of materials» inter-esting results of investigations of the joints producedwith application of nanomaterials were presented. As

basis for such experiments the data published in worksof Soviet scientists were used.

Rather interesting was presentation of V.E.Soshkin et al. «State-of-the-art efficient fiber refrac-tory materials for high-temperature insulation of non-organic binders» which suggested new ways for solu-tion of thermal insulation issues, in particular, in vac-uum furnaces.

Big number of interesting presentations were madeby employees of TSU. Among them one has to note workof R.S. Luchkin «Diffusion model of reliability of brazedunits of copper alloys under conditions of electrochemi-cal corrosion», presentations made by A.Yu. Kras-nopevtsev «Brazing of high-alloy steels in low vacuumand argon» and B.N. Perevezentsev «Influence of alloy-ing elements on mechanical properties of titanium struc-tures brazed with aluminium-base braze alloys». Thelatter work is important from the viewpoint of serialproduction of titanium honeycomb structures.

Actively works in Russia (Moscow) «Union ofprofessional brazing operators» under management ofI.N. Pashkov. On behalf of this Union a number ofpapers were presented which mainly concerned theirparticular issues, but, undoubtedly, containing usefulinformation for the industry. One has to especiallynote efforts of this Union in organization of trainingprocess in higher educational institutions of Russiawith specializing in brazing (with participation ofV.S. Novosadov). It is known that invaluable contri-bution in this field was made by employees of TSU.This experience will be used on all-Russia scale.

It should be noted that in Russia continue to ac-tively work such companies as Alarm, MIFI-Ameto(Moscow) which ensure provision of Russian enter-prises with braze alloys on different bases for widerange of materials. In papers on behalf of these com-panies their latest achievements were reflected.

Low-temperature brazing was presented at the con-ference by informative presentations of E.S. Nazarov(SPE «KVP Raduga» Ltd, Moscow) and N.P.Litvinenko (FSUE SPE «Istok», Fryazino).

Assessing work of the conference as a whole, oneshould note increased activity of Russian specialistsin this field, appearance of a big galaxy of scientistsand production workers which occupy leading posi-tions in development of braze alloys, fluxes, technolo-gies, and preparation of training programs. Still thereare few fundamental works carried out with involve-ment of state-of-the-art methods of investigations, butavailable scientific potential will allow doing this innear future, moreover that active interaction of Russiaand Europe is evident.

One can not but note good, as usually, organizationof the conference, exceptional kindness to guests ofthe TSU employees. One wishes to express them biggratitude and further successes.

V.F. Khorunov, Cor.-Member of the NASof Ukraine, PWI

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INDEX OF ARTICLES FOR TPWJ’2008, Nos. 1--12BRIEF INFORMATIONAnalysis of the causes of fracture of blades in axial-flowcompressor of unit GTK-25I (Yushchenko K.A., SavchenkoV.S., Chervyakova L.V., Izbash V.I. and Solyanik V.G.) 7

Application of explosion energy for treatment of weldedjoints on decomposers and mixers at the Nikolaev AluminaPlant (Dobrushin L.D., Petushkov V.G. and BryzgalinA.G.) 5

Calibration of an optical system for evaluation of tempera-ture field distribution in the welding zone (Kolyada V.A.and Shapovalov E.V.) 4

Influence of network voltage fluctuation on process ofpulsed arc welding (Zhernosekov A.M.) 2

News 1--6, 8--10

On issue of brazing metals using powder braze alloys ofdifferent dispersity (Pismenny A.S., Shvets V.I., Kuchuk-Yatsenko V.S. and Kislitsyn V.M.) 12

Optimization of the geometry of current-conducting nozzletip for mechanized arc welding (Abramov A.A. andZavgorodny V.V.) 1

Reduction of evacuation time of large-sized vacuum cham-bers of electron beam welding installations (NazarenkoO.K.) 3

Theses for scientific degree 2, 8, 9, 12

Upgraded equipment for AUST of end sections of pipes (NajdaV.L., Mozzhukhin A.A., Lobanov O.F., Ignatenko V.A., Ole-jnik Yu.A., Efimov I.V., Kopylov A.P. and Zakharov A.F.) 6

DEVELOPED at PWI 1--7, 9, 10, 12

50 years of electron beam welding at theE.O. Paton Electric Welding Institute 10

FROM HISTORY OF WELDINGDevelopment and progress of arc welding in active gases(Litvinov A.P.) 7

Transition to integrated development of welding production(Kornienko A.N. and Litvinov A.P.) 3

INDUSTRIALAdjustment of thermal power of hydrogen-oxygen flame atflame treatment (Korzh V.N. and Popil Yu.S.) 2

Agglomerated fluxes ---- new products of OJSC «Zaporozh-stekloflyus» (Golovko V.V., Galinich V.I., GoncharovI.A., Osipov N.Ya., Netyaga V.I. and Olejnik N.N.) 10

Application of 10KhSNDA, 15KhSNDA rolled stock in met-al structures of the railway-road bridge across the Dnieperriver in Kiev (Kovtunenko V.A., Gerasimenko A.M.,Zadorozhny V.A. and Ryndich V.V.) 9

Carbide phases and damageability of welded joints of steampipelines under creep conditions (Dmitrik V.V., TsaryukA.K. and Konyk A.I.) 3

Change of mechanical properties of welded joints of carbonand low-alloyed steels at electromagnetic impact (TsaryukA.K., Skulsky V.Yu., Moravetsky S.I. and Sokirko V.A.) 7

Characteristic defects in FSW of sheet aluminium alloysand main causes for their formation (Poklyatsky A.G.) 6

Determination of cyclic fatigue life of materials and weldedjoints at polyfrequency loading (Kovalchuk V.S.) 12

Development and application of tubular welded structures(Garf E.F. and Snisarenko V.V.) 5

Electroslag surfacing of rotating kiln gear shaft teeth(Kozulin S.M., Lychko I.I. and Podyma G.S.) 5

Ensuring the stability of submerged-arc welding process atlow current density (Dragan S.V. and Yaros Yu.A.) 1

E.O. Paton Electric Welding Institute Technology Park --operation experience and prospects (Mazur A.A.) 1

Experience and prospects of using equipment for weldingof rails in Peoples Republic of China (Ma P. and BondarukA.V.) 10

Experimental estimation of carrying capacity of butt weldedjoints of structural shapes in elements of structures sub-jected to low-cycle load (Yavorsky Yu.D., Kuchuk-Yat-senko S.I. and Losev L.N.) 4

Experimental facility for research on pulsed laser-micro-plasma welding (Kirichenko V., Gryaznov N. and Krivt-sun I.) 8

French Institute of Welding today (Bernadsky V.N.) 7

Hyperbaric dry underwater welding (Review) (KononenkoV.Ya.) 4

Improvement of service reliability of double-wall weldedtanks (Barvinko A.Yu.) 3

Improvement of tribotechnical characteristics of hardfacedcast iron automobile crankshafts (Krivchikov S.Yu.) 12

Laser-assisted hardening and coating processes (Review)(Khaskin V.Yu.) 12

Laser-based welding and brazing in automotive produc-tion ---- investigations to reduce failures and imperfections(Albert F., Grimm A., Kageler C. and Schmidt M.) 6

Metal-abrasive grinding wastes, methods of their processingand experience of application in surfacing materials (Len-tyugov I.P., Ryabtsev I.A., Kuzmenko O.G. and KuskovYu.M.) 9

Methods of manufacturing and application of rapidlyquenched braze alloy (Pashkov I.N., Iliina I.I., Rodin I.V.,Shokin S.V. and Tavolzhansky S.A.) 6

Nature of fracture of welded joints of 10Kh13G18D +09G2S steels at vibration loads (Gedrovich A.I., TkachenkoA.N., Tkachenko S.N. and Elagin V.P.) 7

On theory of solution of invention tasks (Mozzhukhin A.A.) 8

Performance of flash butt welded joints on railway frogs(Kuchuk-Yatsenko S.I., Shvets Yu.V., KavunichenkoA.V., Shvets V.I., Taranenko S.D. and Proshchenko V.A.) 9

Prediction of the size of granules and efficiency of theirproduction in centrifugal spraying of alloys (MakhnenkoV.I., Zhudra A.P., Velikoivanenko E.A., Bely A.I. andDzykovich V.I.) 4

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Procedure for repair of blades of titanium alloy VT3-1 byelectron beam welding (Zagornikov V.I.) 5

Remote training model of bachalor-welder (FomichyovS.K., Lopatkin I.E., Lopatkina K.G. and Vasilenko E.I.) 1

Safe level of electromagnetic field intensity in resistancewelding (Levchenko O.G. and Levchuk V.K.) 5

Selection of wire for mechanized arc welding of similar anddissimilar joints of 10Kh13G18D steel (Gedrovich A.I.,Tkachenko S.A. and Kalenskaya A.V.) 1

Series of «Chajka» machines for resistance butt welding ofband saws, wires and rods (Chajka V.G., Volokhatyuk B.I.and Chajka D.V.) 10

State-of-the-art and prospects of development of laser tech-nologies for deposition of coatings and surface hardening(Review) (Khaskin V.Yu.) 2

Technology of spot arc welding of three-layer steel panelwith cellular filler (Lobanov L.M., Timoshenko A.N., Gon-charov P.V. and Zajtsev V.I.) 2

Technology peculiarities of high-frequency seam braze-welding of pipes (Pismenny A.S., Novikova D.P., Yuk-himenko R.V., Prokofiev A.S., Pismenny A.A., PolukhinV.V. and Polukhin Vl.V.) 2

Up-to-date equipment of the E.O. Paton Electric WeldingInstitute for electron beam welding (Nazarenko O.K.) 10

Welding of butt joints of bridge structures and pipelinesusing flux-cored wire and equipment for metal transfercontrol (Karasyov M.V., Rabotinsky D.N., Alimov A.N.,GrebenchukV.G., Golovin S.V. and Rosert R.) 10

NEWSActual problems of welding consumable production (ac-cording to results of broadened meeting of «Electrode»Association of CIS countries) 10

Conference «Brazing-2008» in Toliatti 12

Exhibition «Welding. Allied Technologies ---- 2008» in Kiev 6

Fourth International Conference «Mathematical Modellingand Information Technologies in Welding and Allied Proc-esses» 9

International Conference «Nanosize Systems. Structure--Properties--Technologies» 1

International Conference «Titanium-2008 in CIS» 9

International Conference «Welding and Allied Technolo-gies in Construction, Reconstruction and Maintenance ofPipelines» 1

61st Annual Assembly of International Institute of Welding 10

Technical workshop of welding specialists in Simferopol 12

The First International Conference «Joining AluminiumStructures» 2

To 80th anniversary of Prof. Boris A. Movchan 5

To 100th anniversary of V.I. Dyatlov 1

Workshop-Forum of PII «Binzel Ukraine GmbH» in Kiev 1

NON-DESTRUCTIVE TESTINGDetermination of crack dimensions in welded joints usingultrasonic diffraction waves (Davydov E.A.) 3

PLENARY PAPERS FOR INTERNATIONALCONFERENCE ON WELDING AND RELATEDTECHNOLOGIES INTO THE THIRD MILLENNIUMAdvanced joining technologies of advanced aeronauticalmaterials in China (Xiao-Hong Li, Wei Mao, Hua-PingXiong, Shao-Qing Guo and Hong Yuan.) 11

Advanced welding technologies in recent industries in Japan(Review) (Fujita Y., Nakanishi Y. and Yurioka N.) 11

Application of fracture mechanics methods for assessmentof strength of welded structures (Panasyuk V.) 11

Corrosion cracking of chromium-nickel steels in high-pa-rameter water (Zubchenko A.S.) 11

Deformation-energy aspects and practical applications ofexplosion welding process (Lysak V.I. and Kuzmin S.V.) 11

Development of automatic thermal cutting processes inshipbuilding, metallurgical and mechanical engineering en-terprises (Gorbach V.D. and Nikiforov N.I.) 11

Diagnostics of structures using methods of electronshearography and speckle-interferometry (Lobanov L.M.and Pivtorak V.A.) 11

Education and training in welding and testing of materials(Keitel S. and Ahrens C.) 11

Glorious Jubilee 11

Improving the global quality of life through optimum useof welding technology (Smallbone C.) 11

Intermetallics based on titanium and nickel for advancedengineering products (Kablov E.N. and Lukin V.I.) 11

Laser techniques in modern welding technology. Researchand applications (Pilarczyk J., Banasik M., Dworak J. andStano S.) 11

Mechanical dimensional effects in two-phase inorganic ma-terials (Movchan B.A.) 11

Metallurgy of arc welding of structural steels and weldingconsumables (Pokhodnya I.K.) 11

Micro-welding of stainless steel foil by high-speed laserscanning (Okamoto Y., Gillner A., Olowinsky A.,Gedicke J. and Uno Y.) 11

Modern non-destructive testing means ---- main tool forstructure condition evaluation (Alyoshin N.P.) 11

Modern tendencies in the erection-welding works (Be-loev M.) 11

Monitoring the friction stir welding process of aluminumand magnesium alloys (Dehelean D., Cojocaru R., Radu B.and Safta V.) 11

New aspects in weldability research ---- prerequisites fortechnology and quality assurance in the welding process(Herold H.) 11

New developments to overcome cold cracking in weldedmartensitic creep-resistant steels (Mayr P. and Cerjak H.) 11

Plasma nanopowder metallurgy (Tsvetkov Yu.V. andSamokhin A.V.) 11

Prospects of welding research development in Latin Amer-ica countries on the example of Brazil (Scotti A.) 11

Scientific-technical problems in the field of life assuranceof building structures (Krivosheev P.I., Slyusarenko Yu.S.and Lyubchenko I.G.) 11

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Technology and equipment for flash-butt welding of high-strength rails (Kuchuk-Yatsenko S.I., Didkovsky A.V. andShvets V.I.) 11

Theoretical and experimental investigations of brittle frac-ture resistance of metal of welded structures for the Arcticshelf (Gorynin I.V. and Iliin A.V.) 11

Trends in joining technology (Middeldorf K. and vonHofe D.) 11

Two examples of mathematical modelling in the field ofspecial electrometallurgy: remelting processes and metalnitriding (Jardy A. and Ablitzer D.) 11

Welding and cladding of heat-resistant nickel alloys withsingle-crystal structure (Yushchenko K.A., Zadery B.A.,Savchenko V.S., Zvyagintseva A.V., Gakh I.S. andKarasevskaya O.P.) 11

Welding and joining ---- key technologies for the third mil-lennium (Dilthey U.) 11

Welding and related technologies for medical applications(Paton B.E.) 11

Welding telerobotic system applying laser vision sensingand graphics simulation (Wu L., Li H.C., Gao H.M. andZhang G.J.) 11

What is new with the ISO standard 3834:2005? (vonHofe D.) 11

SCIENTIFIC AND TECHNICALAccumulation of fatigue damage in tee welded joints of09G2S steel in the initial condition and after strengtheningby high-frequency mechanical peening (Knysh V.V.,Solovej S.A. and Kuzmenko A.Z.) 10

Analysis of risk of hot crack formation in braze-weldedtitanium-aluminium joints on basis of mathematical mod-eling (Makhnenko V.I. and Milenin A.S.) 2

Application of laser technology for sintering of the toolcomposites containing diamonds (Golovko L.F., AnyakinM.I., Ehsan O., Novikov N.V., Shepelev A.A. and Soro-chenko V.G.) 8

Application of nanotechnology of permanent joining of ad-vanced light-weight metallic materials for aerospace engi-neering (Paton B.E., Ishchenko A.Ya. and Ustinov A.I.) 12

Calculation-experimental evaluation of the efficiency of al-loying the high-alloy deposited metal with phosphorus (Ry-abtsev I.I.) 5

Calculation prediction of overall distortions in laser weldedbeams (Makhnenko O.V. and Seyffarth P.) 3

Characteristics of fracture resistance of pipeline materialwithin the zone of defects, risk of failure (Makhnenko V.I.,Velikoivanenko E.A. and Olejnik O.I.) 7

Correction of a manipulation robot motion path taking intoaccount additional measurements (Tsybulkin G.A.) 5

Corrosion fatigue resistance of welded joints strengthenedby high-frequency mechanical peening (Knysh V.V., Val-teris I.I., Kuzmenko A.Z. and Solovej S.A.) 4

Current capabilities of simulation of austenite transforma-tions in low-alloyed steel welds (Grigorenko G.M., KostinV.A. and Orlovsky V.Yu.) 3

Determination of parameters of simplified static corrosioncrack resistance diagram for pipe steels in soil corrosion(Makhnenko V.I., Shekera V.M. and Onoprienko E.M.) 10

Effect of alloying of high-strength weld metal with titaniumon its structure and properties (Golovko V.V. and GrabinV.F.) 1

Effect of longitudinal magnetic field on characteristics ofthe arc in TIG welding in argon atmosphere (RazmyshlyaevA.D., Mironova M.V. and Deli A.A.) 3

Effect of microplasma spraying parameters on structure,phase composition and texture of hydroxyapatite coatings(Borisov Yu.S., Borisova A.L., Tunik A.Yu., KarpetsM.V., Vojnarovich S.G., Kislitsa A.N. and Kuzmich-Yanchuk E.K.) 4

Effect of parameters of mechanical-chemical synthesis onstructure, phase composition and properties of thermalspraying Al--Cu--Fe system powders containing quasi-crys-talline phase (Borisova A.L., Borisov Yu.S., Adeeva L.I.,Tunik A.Yu., Karpets M.V. and Burlachenko A.N.) 9

Effect of physical-mechanical properties of the materialsjoined and geometry of the parts on distribution of stressesduring diffusion bonding in vacuum (Makhnenko V.I.,Kvasnitsky V.V. and Ermolaev G.V.) 1

Effect of the type of concurrent gas flow on characteristicsof the arc plasma generated by plasmatron with anode wire(Kharlamov M.Yu., Krivtsun I.V., Korzhik V.N., PetrovS.V. and Demianov A.I.) 6

Effect of zirconia on properties of slag in flux-cored wiresubmerged-arc surfacing using flux AN-348A (SokolskyV.E., Roik A.S., Kazimirov V.P., Ryabtsev I.I., Mish-chenko D.D., Ryabtsev I.A., Kotelchuk A.S. and TokarevV.S.) 7

Electroslag cladding of end surfaces of parts by using slagpool double-loop power circuit (Zorin I.V., Sokolov G.N.,Artemiev A.A. and Lysak V.I.) 1

Estimation of vertical displacement of flyer metal platesbefore contact point in explosion welding (Silchenko T.Sh.,Kuzmin S.V., Lysak V.I., Gorobtsov A.S. and DolgyYu.G.) 4

Improvement of ChS-104 nickel-base alloy weldability byoptimization of heat treatment mode (Maly A.B.) 8

Improvement of delayed cracking resistance of weldedjoints of cast hardenable steels (Poznyakov V.D.) 5

Increase of efficiency of thermal straightening of weldedthin-sheet structures on basis of mathematical modeling(Makhnenko O.V.) 9

Influence of electromagnetic treatment on residual weldingstresses in welded joints of carbon and low-alloyed steels(Tsaryuk A.K., Skulsky V.Yu., Moravetsky S.I. andSokirko V.A.) 9

Influence of friction stir welding process parameters onweld formation in welded joints of aluminium alloys 1.8--2.5mm thick (Poklyatsky A.G., Ishchenko A.Ya. and Podiel-nikov S.V.) 10

Influence of manufacturing technology on the structure andproperties of fused fluxes (Sokolsky V.E., Roik A.S., Kaz-imirov V.P., Tokarev V.S., Goncharov I.A., Galinich V.I.,Mishchenko D.D. and Shevchuk R.N.) 1

Influence of nonmetallic inclusions in low-alloyed steels ontheir weldability in flash-butt welding (Kuchuk-YatsenkoS.I., Zagadarchuk V.F., Shvets V.I. and Gordan G.N.) 6

Influence of oxide film macroinclusions on the strength ofwelds in plate joints of AMg6 alloy (Poklyatsky A.G.) 9

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Mechanical properties of weld metal and cold cracking re-sistance of tee-joints on 13KhGMRB steel (PoznyakovV.D.) 2

Mechanism of the effect of scandium on structure and me-chanical properties of HAZ of the arc welded joints onaluminium alloy V96 (Khokhlova Yu.A., Chajka A.A. andFedorchuk V.E.) 12

Modeling of residual stresses in laser welding (Bokota A.and Piekarska W.) 6

Modelling of the processes of evaporation of metal and gasdynamics of metal vapour inside a keyhole in laser welding(Krivtsun I.V., Sukhorukov S.B., Sidorets V.N. andKovalev O.B.) 10

Numerical simulation of metal structure in HAZ in weldingof increased strength steel (Pekarska V.) 4

On the influence of small parameters on MIG/MAG weld-ing stability (Tsybulkin G.A.) 8

Peculiarities of base metal penetration in arc surfacing inlongitudinal magnetic field (Razmyshlyaev A.D. and Mi-ronova M.V.) 8

Peculiarities of impact toughness tests of automatic flashbutt welded joints on pipes (Kuchuk-Yatsenko S.I., KirianV.I., Kazymov B.I., Mirzov I.V. and Khomenko V.I.) 10

Peculiarities of plastic deformation of near-weld zone metalin explosion welding according to scheme of double-sidedsymmetrical cladding (Kuzmin S.V., Chuvichilov V.A. andLysak V.I.) 5

Physical and technological aspects of braze-welding of ti-tanium-aluminium joints (Review) (Milenin A.S.) 4

Properties of microplasma powder welded joints on heat-resistant nickel alloys (Yushchenko K.A., Yarovitsyn A.V.and Zvyagintseva A.V.) 9

Quality assessment of laser-welded joints of die-cast mag-nesium alloys (Kolodziejczak P. and Kalita W.) 6

Reversible temper brittleness of welded joints of WWERreactor bodies (Kasatkin O.G.) 2

Risk analysis as a method for formalising decision makingon unscheduled repair of welded structures (MakhnenkoV.I., Velikoivanenko E.A. and Olejnik O.I.) 5

Selection of filler metals for brazing thin-walled heat ex-changing devices (Khorunov V.F. and Maksymova S.V.) 3

Selection of technologies for repair of defects in active mainpipelines (Makhnenko V.I., Velikoivanenko E.A. and Ole-jnik O.I.) 6

Sensitivity to cracking and structural changes in EBW ofsingle crystals of heat-resistant nickel alloys (YushchenkoK.A., Zadery B.A., Zvyagintseva A.V., Kotenko S.S.,Polishchuk E.P., Savchenko V.S., Gakh I.S. andKarasevskaya O.P.) 2

Stabilisation of electrode melting rate in robotic arc welding(Tsybulkin G.A.) 12

Stress-strain state of diffusion bonds between metals withdifferent physical-mechanical properties (Makhnenko V.I.,Kvasnitsky V.V. and Ermolaev G.V.) 8

Structure of deposited metal of the type of graphitisedhypereutectoid steels (Kondratiev I.A., Ryabtsev I.A.,Bogajchuk I.L. and Novikova D.P.) 7

System for TIG welding process control of low-thicknesssteels (Kunkin D.D.) 12

Taking into account of high-frequency mechanical peeninginfluence on cyclic working life of welded joints at dou-ble-frequency loading (Kovalchuk V.S.) 3

Theoretical investigation of dynamic behavior of moltenpool in laser and hybrid welding with deep penetration(Turichin G., Valdaitseva E., Pozdeeva E., Dilthey U. andGumeniuk A.) 7

Index of articles for TPWJ’2007, Nos. 1--12 12

List of authors 12

46 12/2008

LIST OF AUTHORS

Ablitzer D. No.11Abramov A.A. No.1Adeeva L.I. No.9Ahrens C. No.11Akhonin S.V. No.9Albert F. No.6Alimov A.N. No.10Alyoshin N.P. No.11Anyakin M.I. No.8Artemiev A.A. No.1

Banasik M. No.11Barvinko A.Yu. No.3Beloev M. No.11Bely A.I. No.4Bernadsky V.N. No.7Bogajchuk I.L. No.7Bokota A. No.6Bondaruk A.V. No.10Borisov Yu.S. No.4, 9Borisova A.L. No.4, 9Bryzgalin A.G. No.5Burlachenko A.N. No.9

Cerjak H. No.11Chajka A.A. No.12Chajka D.V. No.10Chajka V.G. No.10Chervyakova L.V. No.7Chuvichilov V.A. No.5Cojocaru R. No.11

Davydov E.A. No.3Dehelean D. No.11Deli A.A. No.3Demianov A.I. No.6Didkovsky A.V. No.11Dilthey U. No.7, 11Dmitrik V.V. No.3Dobrushin L.D. No.5Dolgy Yu.G. No.4Dragan S.V. No.1Dworak J. No.11Dzykovich V.I. No.4

Efimov I.V. No.6Ehsan O. No.8Elagin V.P. No.7Ermolaev G.V. No.1, 8

Fedorchuk V.E. No.12Fomichyov S.K. No.1Fujita Y. No.11

Gakh I.S. No.2, 11Galinich V.I. No.1, 10Gao H.M. No.11Garf E.F. No.5Gedicke J. No.11Gedrovich A.I. No.1, 7Gerasimenko A.M. No.9Gillner A. No.11Golovin S.V. No.10

Golovko L.F. No.8Golovko V.V. No.1(2), 10Goncharov I.A. No.1, 10Goncharov P.V. No.2Gorbach V.D. No.11Gordan G.N. No.6Gorobtsov A.S. No.4Gorynin I.V. No.11Grabin V.F. No.1Grebenchuk V.G. No.10Grigorenko G.M. No.3Grimm A. No.6Gryaznov N. No.8Gumeniuk A. No.7

Herold H. No.11von Hofe D. No.11(2)Hong Yuan No.11Hua-Ping Xiong No.11

Ignatchenko P.V. No.10Ignatenko V.A. No.6Iliin A.V. No.11Iliina I.I. No.6Ishchenko A.Ya. No.10, 12Izbash V.I. No.7

Jardy A. No.11

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