effect of a high magnetic field on microestructures of ni-based superalloy during directional...

7/23/2019 Effect of a High Magnetic Field on Microestructures of Ni-based Superalloy During Directional Solidification_Xuan_R

1/8

Effect of a high magnetic field on microstructures of Ni-based superalloy

during directional solidification

Weidong Xuan , Zhongming Ren, Chuanjun Li

Shanghai Key Laboratory of Modern Metallurgy & Materials Processing, Shanghai University, Shanghai 200072, China

a r t i c l e i n f o

Article history:

Received 14 July 2014

Received in revised form 7 September 2014

Accepted 13 September 2014

Available online 20 September 2014

Keywords:

Nickel-based superalloy

High magnetic field

Directional solidification

Microstructure

Columnar to equiaxed transition

Primary dendrite arm spacing

a b s t r a c t

The effect of a high magnetic field on the dendrite morphology of superalloy DZ417G during directional

solidification at a low solidification velocity has been investigated experimentally. It was found that the

magnetic field induces columnar to equiaxed transition (CET) and makes the primary dendrite arm spac-

ing decrease. In addition, the magnetic field causes deformation of the solidliquid interface shape and

the macrosegregation in the mushy zone. Based on these results, it was found that both of the thermo-

electric magnetic convection (TEMC) and the thermoelectric magnetic force (TEMF) cause CET, the change

of solidliquid interface shape and the formation of macrosegregation. This is in good agreement with

predicted values of the TEMC and TEMF, respectively. The primary dendrite arm spacing was changed

by the interdendritic TEMC in the magnetic field.

2014 Elsevier B.V. All rights reserved.

1. Introduction

In the past decades, directional solidification (DS) technology

has been widely used to the production of turbine blades of Ni-

based superalloy with complex geometries. The aims of directional

solidification turbine blades are to produce a columnar dendrite

structure along the [00 1] orientation growth because Ni-based

superalloys have the most favorable mechanical properties at the

[00 1] orientation compared with other orientations. Therefore,

the columnar dendrite arm spacing (primary dendrite arm spacing)

plays a main role in determining the mechanical properties of

DS turbine blades [1,2]. In industrial production, DS turbine

blades are usually obtained by Bridgman high rate solidification

technology [3]. However, limited temperature gradient resulting

from Bridgman high rate solidification technology results in

coarse-dendrite and serious element segregation, which signifi-

cantly influence the mechanical properties of DS turbine blades[1].

In order to obtain a good mechanical property of DS turbine

blades, many techniques have been developed to refine dendrite

and decrease element segregation, such as liquid metal cooling

(LMC) [4,5], zone melting liquid metal cooling (ZMLMC) [2] and

gas cooling casting (GCC) [6]. However, it is difficult to further

reform their performances because these techniques are primarily

found on reforming the thermal gradient and cooling rate, and

their practical process conditions are limited during directionalsolidification.

In recent decade, a high magnetic field has been applied during

the solidification of metal materials and many studies indicated

that a high magnetic field could influence many aspects of solidifi-

cation such as phase transformation temperature[7], orientation

[810], inter-lamellar spacing or dendrite spacing [7,11,12],

solidification rate [13] and solute distribution [12,14]. Therefore,

the above works show a possibility to control the microstructure

(e.g. dendrite spacing, element segregation and grain defects) by

high magnetic field for improving the mechanical properties of

superalloy. Subsequently, some researchers have applied a high

magnetic field to the process of directional solidification of super-

alloy[1517]based on above works, whose results showed that a

high magnetic field can obviously change dendrite arm spacing and

element segregation for directionally solidified superalloy. These

researchers think that the effect of the magnetic field on solidifica-

tion was mostly attributed to so-called thermo-electrical-magnetic

convection and stress. However, convection in melt during

solidification may cause detachment of dendrite arms and lead to

the formation of equiaxed grains and segregation of solutes, such

as freckles [18]. Therefore, the effect of high magnetic field on

microstructures of superalloy is also still far from being completely

understood. It is necessary to deeply explore the mechanism of

microstructures of directionally solidified Ni-based superalloy

under the high static magnetic field. The aim of present work is

to experimentally investigate the effect of a high magnetic field

http://dx.doi.org/10.1016/j.jallcom.2014.09.114

0925-8388/ 2014 Elsevier B.V. All rights reserved.

Corresponding author. Tel.: +86 21 56334042.

E-mail address:[email protected](W. Xuan).

Journal of Alloys and Compounds 620 (2015) 1017

Contents lists available at ScienceDirect

Journal of Alloys and Compounds

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j a l c o m
http://dx.doi.org/10.1016/j.jallcom.2014.09.114mailto:[email protected]://dx.doi.org/10.1016/j.jallcom.2014.09.114http://www.sciencedirect.com/science/journal/09258388http://www.elsevier.com/locate/jalcomhttp://www.elsevier.com/locate/jalcomhttp://www.sciencedirect.com/science/journal/09258388http://dx.doi.org/10.1016/j.jallcom.2014.09.114mailto:[email protected]://dx.doi.org/10.1016/j.jallcom.2014.09.114http://crossmark.crossref.org/dialog/?doi=10.1016/j.jallcom.2014.09.114&domain=pdf


2/8

on microstructures of superalloy during directional solidification.

Meanwhile, the changes of interface morphologies for superalloy

during directional solidification are also explored.

2. Experimental procedures

The superalloy DZ417G (C 0.18, Cr 8.96, Mo 3.08, Co 9.72, V 0.86, B 0.015, Al

5.41, Ti 4.50, Fe 0.23, P 0.002, S 0.002, Si 0.04, Mn 0.05, and Ni as balance, wt.%)

was used in this work. The sample with a diameter of 4 mm and a length of150 mm was placed in a corundum tube of high purity for directional solidification

experiment.

The schematic illustration of the directional solidification apparatus is shown in

Fig. 1. It mainly consisted of a static superconducting magnet (Oxford Instrument), a

Bridgman furnace, a withdrawal system and a temperature controller. The super-

conducting magnet could produce a vertical static magnetic field with the maxi-

mum intensity up to 14 T. The furnace temperature was controlled by a

temperature controller with the precision of 1 K. The liquid GaInSn metal

(LMC) pool with a water cooling jacket was used to cool down the sample. The tem-

perature gradient in the sample was controlled by adjusting the temperature of hot

zone of the furnace, which was isolated from the LMC by a refractory baffle. The

withdrawal velocity was controlled by a withdrawing device and could be contin-

uously adjusted between 0.5 lm/s and 104 lm/s.

In the experiments, the sample was heated to a certain temperature (1500C) at

a 10 C/min rate and hold for 30 min, which ensured that the sample was melted

completely and then directionally solidified in the Bridgman apparatus by with-

drawing the crucible assembly downward at a constant withdrawal velocity undervarious magnetic fields. When the sample reached to a steady-state growth stage, it

was quickly quenched into the LMC. During whole experiments, the Bridgman fur-

nace was fluxed with high pure argon to prevent samples from being oxidized. The

temperature gradient in present study was 150 K/cm.

The longitudinal (parallel to the growth direction) and transverse microstruc-

tures of samples were examined by optical microscope in etched condition. The

etchant was composed of CuSO4 (4 g), HCl (20 ml), H2SO4 (12 ml) and H2O

(25 ml). The crystal orientations of samples were investigated by electron backscat-

ter diffraction (EBSD) technology in an Apollo 300 scanning electron microscope

(Obducat CamScan Ltd., Cambridge, UK) equipped with the Channel 5 analysis soft-

ware (Oxford instruments, Oxford, UK). The primary dendrite arm spacings k were

measured by the area counting method on the transverse sections with the equa-

tionk= (A/N)0.5, whereAis the actual area of the region selected and has been given

a certain value in this paper. Nis the average number of primary dendrites in the

areaA .

3. Results

Fig. 2 shows the longitudinal microstructures at the quenched

solidliquid interface of directionally solidification superalloy

DZ417G at the temperature gradient of 150 K/cm and at the with-

drawal velocity of 10 lm/s in various magnetic fields. It can be

observed that a macroscopic nearly planar interface and the

well-ordered columnar dendrite structures were obtained withoutand with a lower magnetic field (B< 0.6 T), as shown inFig. 2ac.

However, when the magnetic field intensity was 0.6 T, a few

columnar dendrites on the edge of sample were fractured and

transformed into equiaxed grains, remaining well grown columnar

dendrites in the center region of the sample, meantime, the macro-

scopic interface shape of sample became convex-up (Fig. 2d). With

the increasing of the magnetic field, the number of equiaxed grains

increased and gradually extended from the edge to the center of

sample (Fig. 2eg). Meanwhile, some freckles macrosegregation

appeared. When the magnetic field increased to 6 T, the equiaxed

grains were grown full of the sample (Fig. 2h). However, the con-

vex shape increased with the increasing of magnetic field and

reached a maximum under a 1.2 T magnetic field. Further increase

of magnetic field results in a sharp decrease of convex shape. How-

ever, when the magnetic field was higher than 4 T, interface shape

became irregular and vortex appeared on the left (Fig. 2g and h).

To visualize the evolution of the microstructure during

directional solidification of superalloy DZ417G under an external

magnetic field, the EBSD technology was used to investigate the

dendrite morphology and crystallogeny orientation ofFig. 2, and

the corresponding EBSD orientation image maps and the inverse

pole figure were shown in Fig. 3 and different colors represent

different crystallogeny orientations. From the EBSD orientation

image maps and the inverse pole figure, it can be observed that

with the comparison of the microstructures without and with a

low magnetic field (B < 0.6 T), a few freely orientated equiaxed

grains on the edge of sample were formed under 0.6 T magnetic

field. With increase of the magnetic field, the number of equiaxed

grains increased and gradually extended from the edge to thecenter of sample. When the magnetic field increased to 6 T, the

freely orientated equiaxed grains were grown full of sample.

In addition, the effect of a high magnetic field on columnar to

equiaxed transition (CET) during directional solidification of super-

alloy DZ417G has been estimated.Fig. 4shows the volume ratio of

equaxied grains in the longitudinal cross-section near the solid

liquid interface ofFig. 2and measures samples with 4 mm in wide

and 1.5 mm in depth from the solidliquid interface. The volume

ratio of equaxied grains in the longitudinal cross-section near the

solidliquid interface of sample is defined as the equiaxed grains

content (Cv) and a content value of 100% means total occupation

by equiaxed grains, on the contrary, a content value of 0 means

total columnar dendrites. It can be observed that the content of

equiaxed grains was obviously increased with increases of themagnetic field and reached to a maximum (70%) under a 1.2 T

magnetic field. Further increases of the magnetic field resulted in

a significant decrease of equiaxed grains content, and then its

contents increased again after reaching a minimum (55%). Finally,

equiaxed grains grew full of the sample.

The corresponding transverse structure at the quenched solid

liquid interface under various magnetic fields was observed.

Fig. 5shows the transverse microstructures of solidified superalloy

DZ417G in mushy zone which was 0.2 mm down from the solid

liquid interface in various magnetic fields. In cases of without

and with a lower magnetic field (B< 0.6 T), the regular arrays of

dendrite structures were homogeneously distributed in the matrix

(Fig. 5a). In comparison, when applying the magnetic field of 0.6 T

(Fig. 5b), a few dendrites became disorder on the edge of the

B Bmax

Heat

insulation

Heating

elements

Curcible

Sample

Superconducting

magnet

Thermal

baffle

Water

cooling

Ga-In-Sn

liquid metal

Water out Water in

Withdrawal

rod

Fig. 1. Schematic illustration of the Bridgman solidification apparatus in the

superconducting magnet.

W. Xuan et al. / Journal of Alloys and Compounds 620 (2015) 1017 11
http://-/?-http://-/?-


3/8

sample and some macrosegregation appeared. With increases of

the magnetic field, the disorder dendrites gradually expanded to

entire region of the sample along with some macrosegregation.

In addition, it was also found that the primary dendrite arm spac-

ing was gradually decreased with increases of the magnetic field.

To achieve a comprehensive understanding, the evolutions ofthe primary dendrite arm spacing in various magnetic fields have

been measured, as shown inFig. 6. It was noticed that the primary

dendrite arm spacing decreased from 245 lm to 190 lm with

increasing the magnetic field from 0 to 2 T. However, when the

magnetic field was higher than 2 T, the primary dendrite arm spac-

ing was not measured because the dendrites were broken and it

was difficult to distinguish the primary dendrites from the high-

order arms.

4. Discussion

The above experimental results indicate that the magnetic field

induces CET and modifies the primary dendrite arm spacing. Inaddition, the solidliquid interface shape was obviously modified

and the macrosegregation appeared in the magnetic field. There-

fore, this means that the external magnetic field can significantly

affect columnar dendrite growth behavior of Ni-based superalloy

DZ417G during directional solidification.

4.1. Variation of microstructure, solidliquid interface shape and

macrosegregation in the high magnetic field

As we know, the macro-interface shape and the primary

dendrite arm spacing are significantly affected by the convections

[1921]. However, in recent years, some researchers have found

that the application of magnetic field can affect flow of electroni-

cally conducting melt[11]. Therefore, the modification of the melt

flow in the high magnetic field could be responsible for the

changes of microstructure and morphology for directionally solid-

ified superalloy DZ417G. Up to date, there are two main types of

effects of magnetic field on melt convection. One is the electro-

magnetic braking (EMB) effect and the other is TEMHD effect.

The EMB effect resulting from interaction between the movingconducting liquid and magnetic field suppresses melt natural

(a2)

B(b1) B(b2)

B(c1) B(c2)

B(d1) B(d2)

B(e1) B(e2)

B(f1) B(f2)

B(g1) B(g2)

B(h1) B(h2)

(a1)

Fig. 2. Longitudinal microstructures near solidliquid interfaces in directionally solidified superalloy DZ417G at the temperature gradient of 150 K/cm and at the withdrawal

velocity of 10 lm/s in various magnetic fields. (a) 0 T, (b) 0.01 T, (c) 0.1 T, (d) 0.6 T, (e) 1.2 T, (f) 2 T, (g) 4 T and (h) 6 T.

12 W. Xuan et al./ Journal of Alloys and Compounds 620 (2015) 1017


4/8

convection, which is both theoretically and experimentally proved

by Utech and Flemings [22]. As a consequence, the regular and

coarse columnar dendrites were obtained during directional

solidification[15,23]. However, present experiment shows a con-

trary result and suggests some convection due to imposition of

the high magnetic field. Thus, in the process of directional solidifi-

cation under the high magnetic field, the changes of microstructure

and morphology should be attributed to the TEMHD effect.

The TEMHD effect resulting from interaction between thermo-electric current and magnetic field induces a new convection. As

we know, for any metal materials, solid and liquid phases usually

have different thermoelectric powers S [24]. If a temperature

gradient rTexists in the solidliquid interface, the thermoelectriccurrent circuitJTEis produced only when the gradients ofSand rT

are not parallel[25].

In the process of directional solidification, the thermoelectric

currents existing in the dendrites and interdendritic melt of mushy

zone have been investigated and analytical expression for thermo-

electric currents in solid and liquid phases is obtained [11]. The

currentsjsin solid dendrites andjLin liquid phase can be expressed

as following[26]:

jS rLrSfLrLfL rSfS

SS SLrT 1

jL

rLrSfL

rLfL rSfSSS SLrT 2

whererL,rSare the electrical conductivity of liquid and solid; fL,fSare the liquid and solid fractions; SL,SSare the thermoelectric power

of liquid and solid, respectively; rT is the temperature gradient.

When an external axial magnetic field is applied, the interaction

between thermoelectric current and magnetic field will produce a

thermoelectric force (TEMF) in solid phase and induce a new flow

in liquid phase, such as thermoelectric magnetic convection (TEMC)

which will promote the mass, heat transport and crystal growth.

Therefore, the CET, modification of the liquidsolid interface shape,

change of the primary dendrite spacing and formation of macroseg-

regation during directional solidification could be attributed to

TEMC in liquid phase and TEMF in solid phase. Recently, some stud-

ies indicated that the orders of magnitude of TEMC are different indifferent scales[27]. The actions of TEMC in liquid phase and TEMF

Fig. 3. EBSD orientation image maps and inverse pole figures (of Fig. 2) for the samples in directionally solidified superalloy DZ417G at the withdrawal velocity of 10 lm/s in

various magnetic fields. (a) 0 T, (b) 0.01 T, (c) 0.1 T, (d) 0.6 T, (e) 1.2 T, (f) 2 T, (g) 4 T and (h) 6 T.

0 1 2 3 4 5 6

0

20

40

60

80

100

Equiaxedgrainscontent,Cv

(%)

Magnetic field,B

(T)

equiaxed grain

Mushy zone

Liquid

Solid

Fig. 4. Effect of the magnetic field intensity B on the content of equaxied grainsCvin the longitudinal cross-section for directionally solidified superalloy DZ417G at

the temperature gradient of 150 K/cm and at the withdrawal velocity of 10 lm/s.

http://-/?-http://-/?-


5/8

(a)

(b) B

(d) B

(e) B

(f) B

(g) B

(h) B

(c) B

Fig. 5. Transverse microstructures of solidified superalloy DZ417G in mushy zone which was 0.2 mm down from the solidliquid interface at the temperature gradient of

150 K/cm and at the withdrawal velocity of 10 lm/s in various magnetic fields.

14 W. Xuan et al./ Journal of Alloys and Compounds 620 (2015) 1017


6/8

in solid phase in the mushy zone during directional solidification ofNi-based superalloy with external magnetic field are shown in

Fig. 7.

When the longitudinal magnetic field interacts with unparallel

thermoelectric currents, the TEMF and TEMC are produced in solid

phase and liquid phase, respectively. At the scale of dendrite, the

clockwise and anticlockwise TEMF exert on the top and bottom

of dendrites in the mushy zone, respectively. Meantime, the TEMC

is generated in the liquid phase near the top of dendrites. At the

scale of sample, the interdendritic TEMC causes the macroscopic

TEMC in the solidliquid interface, which is the same as in the

process of directional solidification under rotating magnetic field

[28], and then the secondary macro-convection may be induced

by the macroscopic TEMC in the vertical direction.

Recently, numerous theoretical[11,29]and experimental stud-ies [30,31] have been conducted to understand the underlying

mechanism of TEMC during directional solidification. Amongst

the theoretical studies, Li et al. [27] has investigated the magni-

tudes of TEMC at different scales in details and found that the fluid

velocity increases as B1/2 in the weak magnetic field and then

decreases as B1 in the strong magnetic field. There should be a

maximum value of fluid velocity when the TEMC is balanced with

viscous friction and the EMB. The corresponding expression of

maximum velocityVmax is following to:

Vmax krrSrT2

q

!1=33

The corresponding magnetic field intensity can be expressed as:

Bmax qrSrT

kr

1=34

where k is the typical length scale and q is the density of the alloyliquid.

According to Eq.(3), we evaluate the maximum velocity of fluid

velocity in the mushy zone of directionally solidified superalloy

DZ417G at the scale of sample (4 mm). The physical parameters

of the Ni-based superalloy are listed in Table 1. We can easily

obtain the maximum velocity Vmax which is about 6.4 102 m/s

and much greater than the growth velocity (withdrawal velocity)

of 10 lm/s in present experiment. It is not difficult to imagine that

the maximum velocity of secondary macro-convection in the ver-

tical direction is much larger even than the actual growth velocity

(withdrawal velocity). As a consequence, these convections lead

to the solute accumulation in the edge regions of the sample near

the solidliquid interface. According to the fundamentals of

solidification, solidification is suppressed in the solute rich regions

and further deepens the solidliquid interface modification. The

corresponding magnetic field intensity is about 1.19 T. However,

present experimental results indicated that the solidliquid inter-

face shape is maximum convex-up in the magnetic field of 1.2 T at

the scale of samples. This means that the intensity of TEMC is the

maximum value in the magnetic field of 1.2 T which is in good

agreement with the theoretical value. With further increases of

magnetic field, the EMB at the sample scale begins to play a great

role in the directional solidification process and the fluid motion is

suppressed. As a consequence, the convex-up amplitude of the

solidliquid interface and the macrosegregation will decrease.

When the magnetic field is strong enough, the fluid motion could

be totally suppressed, and then a macroscopic planar interface

and the well-ordered columnar dendrite structures were obtained

again [15,23]. However, present experiment shows a contrary

result and suggests other effects under a high magnetic field,

which means that the fluid motion should not be the only reason

for the change of interface shape and the formation of equiaxed

grains under the magnetic field.

As we know, when the magnetic field was used for the process

of directional solidification, the TEMF will appear in the dendrite

except for the formation of TEMC in the liquid, which is:

FS rLrSfLrLfL rSfS

SS SLrTB 5

Eq.(5) shows that the TEMF in the solid increases linearly with

the increases of magnetic field intensity. Some researches found

that the TEMF with the order of 105 N/m3 was strong enough to

break down the dendrites [36]. Therefore, it is necessary to

consider the effects of the TEMF on interface morphology and

microstructure in the mushy zone for directionally solidified

superalloy.

0.0 0.5 1.0 1.5 2.0180

190

200

210

220

230

240

250

Primarydendritearms

pacing,

(m)

Magnetic field, B (T)

10m/s

Fig. 6. Effect of the magnetic field intensityBon the primary dendrite arm spacing k

for directionally solidified superalloy DZ417G at the temperature gradient of 150 K/

cm and at the withdrawal velocity of 10 lm/s.

Solid

TEMCTEMF

TE Moment JTE

Liquid

BG(a) BGSecondary macroconvection

TEMC

Liquid

TE Moment

Solid

(b)

TEMF

Fig. 7. Schematic illustrations of TEMC and TEMF on the different scales: (a)

schematic illustration of the TEMC at the dendrite scale and the TEMF imposing on

dendrite and (b) the TEMC at the sample scale, secondary macro-convection and theTEMF exerting on some dendrites.

Table 1

Physical parameters of Ni-based superalloy used for the evaluation.

Physical parameters Magnitude

Electrical conductivity of solid (rS, X1 m1) 1327C 0.75 106 [32]

Electrical conductivity of liquid (rL, X1 m1) 1327 C 0.67 106 [32]

Thermoelectric power of solid (SS, lV K1) 870 C 10.95[33]

Thermoelectric power of liquid (SL, lV K1) 1500 C 16[34]

Density of liquid alloy (q, kg m3), 1427 C 7.3 103 [35]

http://-/?-http://-/?-


7/8

In order to investigate the effects of the TEMF on interface

morphology and microstructure in the mushy zone for directionally

solidified superalloy. We evaluate the magnitude of the TEMF in

the dendrites under various magnetic fields if we take the solid

fraction fS= 0.343, as shown in Fig. 8. It is shown that the TEMF

is larger than 105 N/m3 when the magnetic field is higher than

4 T, which is strong enough to break down the dendrites and the

dendrites are subsequently transformed into equiaxed grains.According to Hunts model [37], the CET is assumed to occur

when the volume fraction of equiaxed grains ahead of columnar

dendrites front exceeds 0.49.

Similarly, the TEMF acting on the equaxied grains from frac-

tured columnar dendrite in the mushy zone can cause the equaxied

grains in liquid phase to rotate, and the corresponding expression

of angular velocity W is following to[38]:

WSG

LB 6

According to Eq. (6), it is found that the angular velocity

decreases with the increases of the grain size and the magnetic

field. Fig. 9shows the angular velocity of equaxied grains in the

mushy zone at 10 lm/s in various magnetic fields. It can be seen

that angular velocity higher than 125 rad/s is strong enough todestroy the dendrite array if we take a grain radius of about

100 lm according to current experimental results. Therefore, the

TEMF acting on the equaxied grains can cause the solidliquid

interface instability and macrosegregation.

4.2. Variation of primary dendrite arm spacing in the high magnetic

field

It is well known that for a given alloy, the dendrite arm spacing

is greatly dependent on the thermal gradient (G) and cooling rate

(GV), but there are some potential effects of convection [19,20]. It

was found that the primary dendrite arm spacing was obviously

decreased in the condition of natural [19] or forced convection

[20,21]. In practice, the primary dendrite spacing is closely associ-ated with the interdendritic constitutional undercooling during

directional solidification [39]. The primary dendrite arm spacing

decreased because the increase of interdendritic undercooling pro-

motes branch of primary dendrite and tertiary dendrite growth,

and then a new primary dendrite was formed. On the contrary,

the primary dendrite spacing increases with the decrease of

interdendritic undercooling. Curreri et al. [40] found that the

convection of fluid can cause the increase of interdendritic

undercooling during directional solidification. Therefore, when

the magnetic field is applied to directional solidification process,

the primary dendrite arm spacing is evidently modified in variousmagnetic fields because the fluid motion is strengthened or atten-

uated by the TEMC or the EMB, respectively. According to Eqs.(3)

and (4), at the scale of dendrite, the maximum values of convection

velocity and corresponding magnetic field are about 0.21 m/s,

5.4 T, respectively. This means that in current experimental

condition of no more than 6 T, the TEMC at the dendrite scale

was dominated. The relationship of the primary dendrite arm spac-

ing and interdendritic convection velocity has been proposed by

Lehmann et al. [11], which shows that the primary dendrite arm

spacing decreases with the increase of convection velocity. Present

experimental results indicated that the primary dendrite arm spac-

ing decreased obviously with increasing the magnetic field. When

the magnetic field was higher than 2 T, the primary dendrite arm

spacing was not measured due to the fact that the dendrites were

broken and it was difficult to distinguish the primary dendrites

from the high-order arms. Therefore, the decreases of primary

dendrite arm spacing should be attributed to the interdendritic

fluid motion induced by the TEMC in the scales of dendrite in the

magnetic field.

5. Conclusions

The effect of a high magnetic field on the microstructures of the

superalloy DZ417G was investigated experimentally during direc-

tional solidification. The results showed that at the withdrawal

velocity of 10 lm/s, the CET occurred in the magnetic field, which

was mainly attributed to the torque generated in the columnar

dendrite by the TEMF. Moreover, the TEMC in the scale of sampleshould also be responsible for the CET. The change of solidliquid

interface shape and macrosegregation could be attributed to the

TEMC in the scale of sample with a lower magnetic field (


8/8

Projects of International Cooperation and Exchanges NSFC (Grant

No. 50911130365). The authors are grateful for this support.

References

[1] C.L. Brundidge, D. Vandrasek, B. Wang, T.M. Pollock, Metall. Mater. Trans. A 43(2012) 965976.

[2] L. Liu, T.W. Huang, J. Zhang, H.Z. Fu, Mater. Lett. 61 (2007) 227230.[3] M. Konter, M. Thumann, J. Mater. Process. Technol. 117 (2001) 386390.[4] J. Zhang, L.H. Lou, J. Mater. Sci. Technol. 23 (2007) 289299.[5] A.J. Elliott, S. Tin, W.T. King, S.-C. Huang, M.F.X. Gigliotti, T.M. Pollock, Metall.

Mater. Trans. A 35 (2004) 32213231.[6] M. Konter, E. Kats, N. Hofmann, Superalloy 2000 (2000) 189195.[7] Y.D. Zhang, C. Esling, M.L. Gong, G. Vincent, X. Zhao, L. Zuo, Scr. Mater. 54

(2006) 18971900.[8] L. Li, Y.D. Zhang, C. Esling, Z.H. Zhao, Y.B. Zuo, H.T. Zhang, J.Z. Cui, J. Mater. Sci.

44 (2009) 10631068.[9] L. Li, Y.D. Zhang, C. Esling, K. Qin, Z.H. Zhao, Y.B. Zuo, J.Z. Cui, J. Appl. Cryst. 46

(2013) 421429.[10] L. Li, Z.B. Li, Y.D. Zhang, C. Esling, H.T. Liu, Z.H. Zhao, Q.F. Zhu, Y.B. Zuo, J.Z. Cui, J.

Appl. Cryst. 47 (2014) 606612.[11] P. Lehmann, R. Moreau, D. Camel, R. Bolcato, J. Cryst. Growth 183 (1998) 690

704.[12] X. Li, Y. Fautrelle, Z.M. Ren, Acta Mater. 56 (2008) 31463161.[13] C. Vives, C. Perry, Int. J. Heat Mass Transfer 29 (1986) 2133.[14] W.V. Youdelis, R.C. Dorward, Can. J. Phys. 44 (1966) 139150.[15] T. Zhang, W.L. Ren, J.W. Dong, X. Li, Z.M. Ren, G.H. Cao, Y.B. Zhong, K. Deng, Z.S.

Lei, J.T. Guo, J. Alloys Comp. 487 (2009) 612617.[16] W.L. Ren, L. Lu, G.Z. Yuan, W.D. Xuan, Y.B. Zhong, J.B. Yu, Z.M. Ren, Mater. Lett.

100 (2013) 223226.[17] X. Li, Z.M. Ren, J. Wang, Y.F. Han, B.D. Sun, Mater. Lett. 67 (2012) 205209.[18] T.M. Pollock, W.H. Murphy, Metall. Mater. Trans. A 27 (1996) 10811094.

[19] M.D. Dupouy, D. Camel, J.J. Favier, Acta Metall. Mater. 40 (1992) 17911801.[20] S. Steinbach, L. Ratke, Metall. Mater. Trans. A 38 (2007) 13881394.[21] J. Hui, R. Tiwari, X. Wu, S.N. Tewari, R. Trivedi, Metall. Mater. Trans. A 33 (2002)

34993510.[22] H.P. Utech, M.C. Flemings, J. Appl. Phys. 37 (1966) 20212024.[23] M.D. Dupouy, D. Camel, J. Cryst. Growth 183 (1998) 469489.[24] S. Yesilyurt, L. Vujisic, S. Moyalkef, F.R. Szofran, M.P. Volz, J. Cryst. Growth 207

(1999) 278291.[25] J.A. Shercliff, J. Fluid Mech. 91 (1979) 231251.[26] R. Moreau, O. Laskar, M. Tanaka, D. Camel, Mater. Sci. Eng. A 173 (1993) 93

100.[27] X. Li, Y. Fautrelle, Z.M. Ren, Acta Mater. 55 (2007) 38033813.[28] G. Zimmermann, A. Weiss, Z. Mbaya, Mater. Sci. Eng. A 413414 (2005) 236

242.[29] Y.Y. Khine, S. Walker, J. Cryst. Growth 183 (1998) 150158.[30] P. Dolda, F.R. Szofranb, K.W. Benz, J. Cryst. Growth 291 (2006) 17.[31] H. Yasuda, T. Yoshimoto, T. Mizuguchi, Y. Tamura, T. Nagira, M. Yoshiya, ISIJ

Int. 47 (2007) 612618.[32] G. Pottlacher, H. Hosaeus, B. Wilthan, E. Kaschnitb, A. Seifter, Thermochim.

Acta 382 (2002) 255267.[33] H. Carreon, Nondestruct. Test Eval. 24 (2009) 233241.[34] B.C. Dupree, J.E. Enderby, R.J. Newport, J.B. Van Zytveld, Inst. Phys. Conf. Ser. 30

(1977) 337341.[35] P.N. Quested, R.F. Brooks, L. Chapman, R. Morrell, Y. Youssef, K.C. Mills, Mater.

Sci. Technol. 25 (2009) 154162.[36] X. Li, Y. Fautrelle, K. Zaidat, A. Gagnoud, Z.M. Ren, R. Moreau, Y.D. Zhang, C.

Esling, J. Cryst. Growth 312 (2010) 267272.[37] J.D. Hunt, Mater. Sci. Eng. 65 (1984) 7583.[38] X. Li, A. Gagnoud, Y. Fautrelle, Z.M. Ren, R. Moreau, Y.D. Zhang, C. Esling, Acta

Mater. 60 (2012) 33213332.[39] K.A. Jackson, J.D. Hunt, D.R. Uhlmann, T.P. Seward, Trans. TMSAIME 236

(1966) 149158.[40] P.A. Curreri, J.E. Lee, D.M. Stefanescu, Metall. Trans., A 19 (1988) 26712676 .

http://refhub.elsevier.com/S0925-8388(14)02275-0/h0005http://refhub.elsevier.com/S0925-8388(14)02275-0/h0005http://refhub.elsevier.com/S0925-8388(14)02275-0/h0010http://refhub.elsevier.com/S0925-8388(14)02275-0/h0015http://refhub.elsevier.com/S0925-8388(14)02275-0/h0015http://refhub.elsevier.com/S0925-8388(14)02275-0/h0020http://refhub.elsevier.com/S0925-8388(14)02275-0/h0020http://refhub.elsevier.com/S0925-8388(14)02275-0/h0025http://refhub.elsevier.com/S0925-8388(14)02275-0/h0025http://refhub.elsevier.com/S0925-8388(14)02275-0/h0030http://refhub.elsevier.com/S0925-8388(14)02275-0/h0035http://refhub.elsevier.com/S0925-8388(14)02275-0/h0035http://refhub.elsevier.com/S0925-8388(14)02275-0/h0040http://refhub.elsevier.com/S0925-8388(14)02275-0/h0040http://refhub.elsevier.com/S0925-8388(14)02275-0/h0045http://refhub.elsevier.com/S0925-8388(14)02275-0/h0045http://refhub.elsevier.com/S0925-8388(14)02275-0/h0050http://refhub.elsevier.com/S0925-8388(14)02275-0/h0050http://refhub.elsevier.com/S0925-8388(14)02275-0/h0055http://refhub.elsevier.com/S0925-8388(14)02275-0/h0055http://refhub.elsevier.com/S0925-8388(14)02275-0/h0060http://refhub.elsevier.com/S0925-8388(14)02275-0/h0065http://refhub.elsevier.com/S0925-8388(14)02275-0/h0070http://refhub.elsevier.com/S0925-8388(14)02275-0/h0075http://refhub.elsevier.com/S0925-8388(14)02275-0/h0075http://refhub.elsevier.com/S0925-8388(14)02275-0/h0080http://refhub.elsevier.com/S0925-8388(14)02275-0/h0080http://refhub.elsevier.com/S0925-8388(14)02275-0/h0085http://refhub.elsevier.com/S0925-8388(14)02275-0/h0085http://refhub.elsevier.com/S0925-8388(14)02275-0/h0090http://refhub.elsevier.com/S0925-8388(14)02275-0/h0090http://refhub.elsevier.com/S0925-8388(14)02275-0/h0095http://refhub.elsevier.com/S0925-8388(14)02275-0/h0100http://refhub.elsevier.com/S0925-8388(14)02275-0/h0105http://refhub.elsevier.com/S0925-8388(14)02275-0/h0105http://refhub.elsevier.com/S0925-8388(14)02275-0/h0110http://refhub.elsevier.com/S0925-8388(14)02275-0/h0115http://refhub.elsevier.com/S0925-8388(14)02275-0/h0115http://refhub.elsevier.com/S0925-8388(14)02275-0/h0120http://refhub.elsevier.com/S0925-8388(14)02275-0/h0120http://refhub.elsevier.com/S0925-8388(14)02275-0/h0120http://refhub.elsevier.com/S0925-8388(14)02275-0/h0125http://refhub.elsevier.com/S0925-8388(14)02275-0/h0130http://refhub.elsevier.com/S0925-8388(14)02275-0/h0130http://refhub.elsevier.com/S0925-8388(14)02275-0/h0135http://refhub.elsevier.com/S0925-8388(14)02275-0/h0140http://refhub.elsevier.com/S0925-8388(14)02275-0/h0140http://refhub.elsevier.com/S0925-8388(14)02275-0/h0145http://refhub.elsevier.com/S0925-8388(14)02275-0/h0150http://refhub.elsevier.com/S0925-8388(14)02275-0/h0150http://refhub.elsevier.com/S0925-8388(14)02275-0/h0155http://refhub.elsevier.com/S0925-8388(14)02275-0/h0155http://refhub.elsevier.com/S0925-8388(14)02275-0/h0160http://refhub.elsevier.com/S0925-8388(14)02275-0/h0160http://refhub.elsevier.com/S0925-8388(14)02275-0/h0165http://refhub.elsevier.com/S0925-8388(14)02275-0/h0170http://refhub.elsevier.com/S0925-8388(14)02275-0/h0170http://refhub.elsevier.com/S0925-8388(14)02275-0/h0170http://refhub.elsevier.com/S0925-8388(14)02275-0/h0175http://refhub.elsevier.com/S0925-8388(14)02275-0/h0175http://refhub.elsevier.com/S0925-8388(14)02275-0/h0180http://refhub.elsevier.com/S0925-8388(14)02275-0/h0180http://refhub.elsevier.com/S0925-8388(14)02275-0/h0185http://refhub.elsevier.com/S0925-8388(14)02275-0/h0190http://refhub.elsevier.com/S0925-8388(14)02275-0/h0190http://refhub.elsevier.com/S0925-8388(14)02275-0/h0190http://refhub.elsevier.com/S0925-8388(14)02275-0/h0195http://refhub.elsevier.com/S0925-8388(14)02275-0/h0195http://refhub.elsevier.com/S0925-8388(14)02275-0/h0195http://refhub.elsevier.com/S0925-8388(14)02275-0/h0200http://refhub.elsevier.com/S0925-8388(14)02275-0/h0200http://refhub.elsevier.com/S0925-8388(14)02275-0/h0195http://refhub.elsevier.com/S0925-8388(14)02275-0/h0195http://refhub.elsevier.com/S0925-8388(14)02275-0/h0190http://refhub.elsevier.com/S0925-8388(14)02275-0/h0190http://refhub.elsevier.com/S0925-8388(14)02275-0/h0185http://refhub.elsevier.com/S0925-8388(14)02275-0/h0180http://refhub.elsevier.com/S0925-8388(14)02275-0/h0180http://refhub.elsevier.com/S0925-8388(14)02275-0/h0175http://refhub.elsevier.com/S0925-8388(14)02275-0/h0175http://refhub.elsevier.com/S0925-8388(14)02275-0/h0170http://refhub.elsevier.com/S0925-8388(14)02275-0/h0170http://refhub.elsevier.com/S0925-8388(14)02275-0/h0165http://refhub.elsevier.com/S0925-8388(14)02275-0/h0160http://refhub.elsevier.com/S0925-8388(14)02275-0/h0160http://refhub.elsevier.com/S0925-8388(14)02275-0/h0155http://refhub.elsevier.com/S0925-8388(14)02275-0/h0155http://refhub.elsevier.com/S0925-8388(14)02275-0/h0150http://refhub.elsevier.com/S0925-8388(14)02275-0/h0145http://refhub.elsevier.com/S0925-8388(14)02275-0/h0140http://refhub.elsevier.com/S0925-8388(14)02275-0/h0140http://refhub.elsevier.com/S0925-8388(14)02275-0/h0135http://refhub.elsevier.com/S0925-8388(14)02275-0/h0130http://refhub.elsevier.com/S0925-8388(14)02275-0/h0130http://refhub.elsevier.com/S0925-8388(14)02275-0/h0125http://refhub.elsevier.com/S0925-8388(14)02275-0/h0120http://refhub.elsevier.com/S0925-8388(14)02275-0/h0120http://refhub.elsevier.com/S0925-8388(14)02275-0/h0115http://refhub.elsevier.com/S0925-8388(14)02275-0/h0110http://refhub.elsevier.com/S0925-8388(14)02275-0/h0105http://refhub.elsevier.com/S0925-8388(14)02275-0/h0105http://refhub.elsevier.com/S0925-8388(14)02275-0/h0100http://refhub.elsevier.com/S0925-8388(14)02275-0/h0095http://refhub.elsevier.com/S0925-8388(14)02275-0/h0090http://-/?-http://refhub.elsevier.com/S0925-8388(14)02275-0/h0085http://-/?-http://refhub.elsevier.com/S0925-8388(14)02275-0/h0080http://refhub.elsevier.com/S0925-8388(14)02275-0/h0080http://-/?-http://refhub.elsevier.com/S0925-8388(14)02275-0/h0075http://refhub.elsevier.com/S0925-8388(14)02275-0/h0075http://-/?-http://refhub.elsevier.com/S0925-8388(14)02275-0/h0070http://-/?-http://refhub.elsevier.com/S0925-8388(14)02275-0/h0065http://-/?-http://refhub.elsevier.com/S0925-8388(14)02275-0/h0060http://-/?-http://refhub.elsevier.com/S0925-8388(14)02275-0/h0055http://refhub.elsevier.com/S0925-8388(14)02275-0/h0055http://-/?-http://refhub.elsevier.com/S0925-8388(14)02275-0/h0050http://refhub.elsevier.com/S0925-8388(14)02275-0/h0050http://-/?-http://refhub.elsevier.com/S0925-8388(14)02275-0/h0045http://refhub.elsevier.com/S0925-8388(14)02275-0/h0045http://refhub.elsevier.com/S0925-8388(14)02275-0/h0040http://refhub.elsevier.com/S0925-8388(14)02275-0/h0040http://refhub.elsevier.com/S0925-8388(14)02275-0/h0035http://refhub.elsevier.com/S0925-8388(14)02275-0/h0035http://refhub.elsevier.com/S0925-8388(14)02275-0/h0030http://refhub.elsevier.com/S0925-8388(14)02275-0/h0025http://refhub.elsevier.com/S0925-8388(14)02275-0/h0025http://refhub.elsevier.com/S0925-8388(14)02275-0/h0020http://refhub.elsevier.com/S0925-8388(14)02275-0/h0015http://refhub.elsevier.com/S0925-8388(14)02275-0/h0010http://refhub.elsevier.com/S0925-8388(14)02275-0/h0005http://refhub.elsevier.com/S0925-8388(14)02275-0/h0005http://-/?-

effect of a high magnetic field on microestructures of ni-based superalloy during directional...

Documents