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Dry friction and wear rates as under liquid lubrication of
Ceramic/ Carbon couples up to 450°C
Jens Kleemann
Rolls-Royce Deutschland Ltd. & Co. KG, D-15827 Dahlewitz/Berlin
Mathias Woydt
Federal Institute of Material Testing and Research, D-12200 Berlin
SummaryIn a high temperature tribometer, stationary carbon have been tested against different rotating Ceramics (SiC,
Si3 N4, Al2O3, WC-6Ni, MgO-ZrO2, (Ti, Mo)(C, N) and stainless steel 1.4876) and the friction and wear behav-
iour have been characterized. The test conditions were chosen as follows:
Normal force Fn = 10 N, sliding velocity v=1-5 m/s, temperature T= 25-500 °C, sliding distance s= 20 km, with
H2O-steam, without intermediate medium and under vacuum. The rotating disks were sharpened, polished and
lapped.
For the most raw material combinations the wear picture is known from the literature. A transfer film with typi-cal wear pattern was found on the rotating disk. With the transfer film lubrication, lowest coefficient of friction
has been found around µ 0,07 in combination with a minimum wear rate of K v 5,010-7
mm³/Nm at 400°C,
v=3 m/s under steam and lapped surface. The combination of antimony graphite EK3245 against MgO-ZrO 2 did
not form carbonaceous transfer layer. Through advanced variation of the roughness up to R PK = 0,011 µm the
wear rate has been reduced up to K v 3.510-8
mm³/Nm at a stable coefficient of friction in a „millirange“ of µ~
0,008 for a sliding distance of 20,000 km. The wear coefficient of EK3245 remains at 4 m/s and temperature of
400°C. As well for the ceramic Al2O3 the coefficient of friction was established in a „millirange“.
With the help of AFM microscope a tribochemical reaction layer has been detected on the used MgO-ZrO 2 ce-
ramic. The identified layer has had a thickness of approximate 50 nm. The chemical elements Zr(OH)4, Sb,
Sb2O3 and Sb2O4 were detected by using Laser Raman and Small Spot ESCA XPS analysis. A carbonaceous
layer could not be confirmed by using these methods of analysis.
A theoretical life time prediction was carried out for the tribological system piston ring/ cylinder in accordance
to the operating conditions of a specific steam engine. The life-time was predicted by means of calculation the
specific (Typical) engine loads and in comparison to the maximum allowable frictional power loss based on the
previously measured wear rates in the low-wear regime. The limits for low-wear/high-wear transitions of the
selected couples were not reached.
1 Introduction
Even under using of latest knowledge from the
research, there is no dry friction mechanism to
substitute the liquid lubrication [1, 2, 3]. Due to
physical characteristics there are boundaries for oils
and greases with regard to high temperature stabil-
ity and –rheology. Above these limits (T>350°C),
where liquid lubricants will be thermal unstably,
dry lubricants can take over the tasks of lubrication
if they have similarly low friction and wear rates.
The use of dry lubricants under boundary condi-
tions has been established for some decades. Inaccording to different applications dry lubricants
exists as pure solid lubricant, gliding varnishes,
coating, as additives inserted in high temperature
materials or as composite up to 1000 °C. Ceramic
engineering materials enforced thereby more and
more.
According to common approach, the tribological
behaviour depends on the formation of a transfer
film on polymer materials [4,5,6,7,8], on extrinsic
or intrinsic solid lubricants [9,10,11], as well as soft
metals [9] (In, Pb, Au) under solid friction [12,].
This well-known wear mechanism is also valid for
Molybdändisulfid [13].
Usually graphite forms also a various pallet of car-
bonaceous reaction products at the transfer layer
[14].
Load, sliding speed, environment, contact geome-
try, roughness adhesion tendency etc. influence the
formation of the layer [15,16].
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-well-defined and constant environment conditions,
like vacuum, hydrogen or nitrogen
The characteristics to form a tribological layer
determins the friction and wear behaviour of poly-
mers and solid lubricants. The surface roughness of
the disk determines the thickness of the transfer
film. For each combination solid lubricant /disk or
Polymer/disk“ an optimal thickness of the layer iswell known. A thickness optimum caused by low
friction and low wear rates. After the run in and
formation of the transfer layer the solid lubricant
runs against itself with more or less no contact to
the counter body. Until the run in is not finished,
the wear rate will be high, because of required ma-
terials transfer.
-environment temperature less than 300°C
-less interactions
-parallel oriented shear layer
Nowadays, such requirements and operating condi-
tions are only relevant in the field of micro
mechanics und astronautics however not in me-
chanical engineering or in the automotive industry.
Tribological reactions [23] represents a further
strategy for reduction of friction and wear. Follow-
ing reactions offer a high potential for reducing
friction and wear:The aim to present sliding couples under solid con-
ditions that are comparable to liquid lubricants can
be fulfilled only by the way of avoidance the trans-
fer film.
a. Adsorption of Water [24,25],
b. Formation of hydroxide [26,27],c. Formation of oxides [28,29] und
d. Vapor phase lubrication [30,31] .2 State of Technology
In this work, the tribological relevance of hydrox-
ides will be outlined. The tribological effects that
were obtained so far through the tribochemical
formation of oxides on non-oxide ceramics is in
detail summarized at [28, 29].
Investigations in the last years at different construc-
tion ceramics under dry frictional conditions up to
high temperatures have shown that coefficients of
friction less than µ 0,1 are not even possible. [17,
18]. At these investigations the wear rates are also
not higher than K v>510-7
mm³/Nm. An overview of
dry friction and wear of ceramics has been given by[19, 20]. Mainly, investigations have been done
under atmospheric standard conditions at sliding
speed around 1 m/s and load of 10 N. The wear
coefficients of k v 110-7
mm3/Nm that were partly
reached caused always friction coefficients of µ
0,3.
Under atmosphere conditions, the reaction between
the ceramic surface and steam will be a natural and
odds-on form of lubrication. In the following this
report work up this subject.
By adding up to 6 % by volume of powdered boron
carbide (B4C) with a grit size between about 100
and about 1500 grit in carbon fiber reinforced car-
bon matrix [32], the coefficient of friction lie in a
range of 0,022 to 0,061 at temperatures up to 600
°C, when sliding against magnesium-aluminium-
silicate disks (P~ 0,137 MPa, v ~ 0,54 m/s). The
composite matrix consists of carbon black filler,
resin char and pyrolitic carbon.
Typical lubricated tribological systems achieve
coefficients of friction between 0,15 till 0,05 under
mixed or boundary conditions. Furthermore the
coefficient of friction will decrease up to 10-3
under
hydrodynamic conditions. Dry running tribologicalsystems should have to show friction coefficients
between 0,001 and 0,015 in order to be competitive
against lubricated systems. 3 Experimental InvestigationFirst in the last years, investigations showed up at
special coatings that friction coefficients are reach-
able under dry conditions up to 10-3
[21, 22]. The
effect of the „gliding without friction“ is tied to the
following conditions:
In these investigation the tribological behaviour of
high temperature ceramics have been characterized
under dry conditions up to 5 m/s sliding speed in
deionizied steam with temperatures up to 500 °C.
Along with the normal force of 10 N, the corre-
sponded initial herzian pressure was p~ 135 N/mm².
The experimental setup was equivalent to tribologi-cal system „Piston ring/ Cylinder“ in accordance to
the steam engine [33]. The stationary probe always
-atomistically smooth surface (roughness 2 nm)
-friction capacity less than 1 mW/mm²
-frequency free elastic micro contact
-no reaction layers on the surface
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consisted from graphite. Characteristic is the self-
lubricated property of graphite as known from dif-
ferent intrinsic or extrinsic solid lubricants.
Various combinations of materials have been tested
in a large use field at a high temperature tribometer
(HTT). All materials were steam degradation resis-tant. The schematic construction of the HTT is
described in [34] and recognizable in Picture 8-1 as
IR-Thermography.
For this purpose, the parameters sliding speed,
temperature, environment, processing and rough-
ness have been varied. A summary of all examined
materials and parameter combinations gives
. In this publication only the combinations graphite
against Al2O3 and against MgO-ZrO2 have been
considered. By means of different analytics, the
presence of tribochemical reaction layer were de-tected and characterized.
4 Experimental Results
On the ceramic disks Si3 N4, SiC, WC-6Ni,
(Ti,Mo)(C,N) and the stainless steel 1.4876 the
presence of carbon could be detected on the wear
track. [Picture 8-3]. In this case, the well known
wear mechanism „graphite gliding took effect. The
minimal achieved wear coefficient was Kv 5,010-
7 mm³/Nm in conjunction with a coefficient of
friction about µ 0,07. This results were found on
lapped SiC- and TM10-probes with a roughness of
R pk = 0,2µm at 400°C in H2O-steam. All other pa-
rameter and topographies resulted in larger friction
coefficients. These results represent only knowl-
edge that is well known from the literature.
The sliding couple Al2O3/ EK3245 and MgO-
ZrO2/EK3245 depart from the rule of formation of
graphite layer. Both oxide ceramics reached dryfriction coefficients about „millirange“, which were
stable over the complete sliding distance (Diagram
8-1).
The light microscopy (Picture 8-2) shows, that
carbon on the Al2O3 ceramic is only detectable in
less concentrations. On the MgO-ZrO2 ceramic the
presence of carbon is only visible in the pores and
not on the surface plateaus (Picture 8-4).
Picture 8-5 make the influence of antimony clear.
This unexpected result has been established in addi-
tional tests. By means of polishing the roughness of
the MgO-ZrO2 ceramic has been reduced up to R pk =
0,011µm. The consequence of smoother surface
was an additional reducing of the coefficient of
friction up to K v 3.510-8
mm³/Nm.
Detected friction coefficients were about µ 0,008.
Corresponding results are representing in Diagram
8-3 and Table 8-2.
Diagram 8-2 shows the coefficient of friction ofgraphite EK3245 as function of the sliding speed.
The coefficient of friction in the range of 10-8
mm³/Nm was found up to 4 m/s between 250 °C
and 450 °C.
Several times repetition has produced identical
results of this ultra low friction and wear.
For comparison reasons, a second antimony im-
pregnated graphite (FH82A) has been tested against
MgO-ZrO2 (R pk = 0,011µm). With a sliding speed of
3 m/s at 400°C the friction coefficient could not
keep down. as previous sliding couple. The friction
coefficient was between 0,02 and 0,025.with a
respective coefficient of wear about K v= 4,010-7
mm³/Nm.
5 Analytical Investigation
By means of surface analytic AFM Microscope,
Laser Raman and Small Spot ESCA, the surface
change of the ceramic MgO-ZrO2-has been ana-lyzed before and after tribological testing. The
focuses of investigations were the formation and
presence of tribochemical layers in the wear track
caused by Graphite, Antimony, Zirconium Oxide
and Steam.
5.1 AFM Microscopy
The in Picture 8-6 presented surface topography
shows the formatted reaction layers in the wear
track on MgO-ZrO2. In the lower unused area of the
100 x 100 µm photo, grain boundaries of each sin-
gle crystal are recognizable. The upper picture area
presents the transition region to the used zone. The
formation of a tribochemical reaction layer has been
detected with the shape of agglomerates. The pro-
file (Picture 8-7) shows the raised layer with a
thickness about 50 nm
5.2 Laser Raman
Laser-Raman is well suitable for structural analysis
of nanocrystalline phases. For the investigation ofthe graphite transfer layer on MgO-ZrO2, the disk
has been scanned with the 488nm Raman-
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Spectrum. Scans has been made into the pores and
on the wear track (Diagram 8-4). The spectrum of
the measurement on the wear track owns in the area
of 1300 cm-1
till 1500 cm-1
only the known fluores-
cence bands of MgO-ZrO2. No typical carbona-
ceous peaks could be found.The measuring in the pore yielded a Raman peak at
1576 cm-1
at 1619 cm-1
. This peak was identified as
carbon [35].
Even though carbon hasn’t been found, Diagram
8-5 shows different results of the intensity under
equal measuring conditions (10 mW Laser power,
90 sec. Count time). In the area of the track, im-
pulses were between 14500 – 22000. Outside the
track impulse about 24000 were detected. The track
seems to be covered with a thin layer, which weak-
ens the laser light as well as the reflected back scat-tered light By means of Small Spot ESCA and XPS
additional investigations has been made.
5.3 Small Spot ESCA XPS
On the unused MgO-ZrO2-ceramic, binding ener-
gies of zirconium Zr 3d5 with 181,5 eV, binding
energies of magnesium Mg2s with 88,1 eV and the
belonging binding energies to oxygen O1s with
529,9 eV have been detected. These binding ener-
gies were allocated to ZrO2 and MgO. Because of
the oxygen peak O2s with 525,8 eV absorbed H2O-
steam was existing on the surface.
Under dry test conditions, the detected Zr- binding
energy showed not difference in according to the
unused MgO-ZrO2-ceramic. The detected peaks
could also assign to ZrO2 and MgO ceramics. Addi-
tional analysis on the wear track produced binding
energy- peaks of antimony Sb4d4. the binding en-
ergy of Sb4d with 33,86 eV could classify to the
metallic antimony. In accordance with the literature
the peak Sb4d with 35,14 eV is Sb2O4. The detected binding energy of O2s with 29,95 eV could assign
to adsorbed H2O.
With the help of Small- Spot- ESCA analysis, on
the wear track of MgO-ZrO2 ceramic zirconium
dioxide peaks Zr3d5 with 181,74 eV and Zr3d3
with 184,21 eV, as well as an unknown zirconium
peak have been detected under H2O steam at 400°C
(Diagram 8-6). The supposition that, it could be a
kind of hydrate or hydroxide has been confirmed by
means of Zr(OH)4-reference powder (Diagram 8-7).The binding energy of Zr3d5 with 183,36 eV and
Zr3d3 with 185,83 eV have been clearly identified
as zirconium hydroxide Zr(OH)4 (CAS: 14475-63-
9, density= 3,25 g/cm³). The binding energies for
zirconium of 183,6 eV for zirconium hydroxyde
were additionally confirmed by [36].
At the consideration of the antimony elements, a
third has been detected compared with metallic andoxide antimony.
Because of missing reference, the third antimony
element could not specified in detail. It could be an
Oxide of antimony with a higher oxidation rate
(Sb2O4+n). (Diagram 8-8).
6 Discussion
During the tests there has been analysed the forma-
tion of a tribochemical reaction layer by using
graphite against MgO-ZrO2 ceramic disks by tem-
perature at 400°C and H2O steam. The formation of
antimony oxide of different oxidation grades could
be evidenced. Due to quantitative analysis a reac-
tion layer of hexagonal agglomerates were found.
The identified layer at the counter disk had a thick-
ness of approx. 40 nm.
There was none indication of clear changes in the
structure of the zirconium oxide ceramic which
improved the behaviour. For the first time graphite
debris which are in condition of formation of trans-
fer layer on ceramics has surprisingly not been
identified. These extremely low friction and wear
rates are subject to a positive combination of vari-
ous parameters.
The major impact is attributed to the zirconium
hydroxide [37] that is thermal stable up to 650°C.
Especially the XPS-data in Figures 8-6 and 8-7
suggests, that hydrous zirconia ZrO2nH2O was not
formed [36].
Referring to various papers, reduction effects on
wear and friction were stated in the formation ofHydroxides and „Pseudo-Hydroxides“ [38] formed
on TiO2-, ZrO2- and Al2O3-surfaces.
Gates [39,40] gave evidence on decreased wear and
friction rates in H2O caused by the formation of a
transfer layer as Al(OH)3 [Gibbsite] or -Al(OH)3
[Bayerite] and Boehmite [-AlO(OH), HV~8.000
MPa] on Al2O3. Relatively weak bonds reflect the
structure of both hydroxides and hydrates. The
difference is only the kind of layer stacking (Picture
8-8).). Boehmite will be formed above 194°C and
Gibbsite above 100°C.
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Gardos [41] investigates the characteristic of oxida-
tion of MoS2 under friction and wear contact. In
this connection he characterised also the influence
of Hydroxides of friction and wear. He describes
the formation of an outer oxidation layer. The layer
consists of MoO3 which has low shear stress.On the boundary layer of MoO3, H2O molecules are
available which are bonded by hydrogen. For this
reason, hydroxides are not impossible. Particularly
the low friction and wear rate of Molybdänhydrox-
ide-Hydrate (Ilsemannite, JCPDS.-Nr. 210574) has
been confirmed [42] in corresponding investiga-
tions. Picture 6-1 shows the coordination of H2O-
molecule between Molybdenum [43]. In this case
[MoO5(OH2)]n is present in an octahedron shape.
Hydrogen bonding connects the different Above
450°C the dehydratation to MoO2,8 is closed.
Picture 6-1 Projection of MoO3x1H2O-Structure
into [001]-direction
The Cobalt hydroxide (Co(OH)2) that was used as
an additive has shown a wear reduction in corre-
sponding investigations [44]. Zirconium hydroxide
has also a layer structure [45] which preferred a
favourable friction and wear characteristic [46].
Picture 6-2 atom model of Sb2O3 Valentinit
The tested graphite EK3245 (with approx. 10%
antimony) had the largest share in antimony of
everybody. The physical properties are similar to
the metallic lead or tin. Because of low shear
strengths these metals are preferred to using into
bearings. At the analytical investigations Sb, Sb2O3
as well as Sb2O4 have been detected.
Sb2O3 [Valentinite, CAS: 1317-98-2, HV~780 MPa,=5,76 g/cm³] is thermodynamic stable in the range
from room temperature up to 370°C. Valentinite
has very long double- bonds, which keep together
with less Sb-O bonds [47].
For this reason Sb2O3 is a preferred additive for
gliding varnishes, for oils or for powders [48].
From 370 °C Sb2O3 reacts very slow exotherm to
Sb2O4 (Cervantit, HV~2,600 MPa). Due to hot envi-
ronment up to 400°C, presence of steam and addi-
tional increase of temperature because of friction
power (hot spots) other oxides of antimony are possible.
As a further influence parameter, the catalytic effect
of graphite, steam and zirconium has to be men-
tioned.
On the one hand, the intercalation of steam into
graphite caused a decrease of shear strength and
reduction of the coefficient of friction.
On the other hand, the steam is reacting with graph-
ite around 400°C. Following reactions are possible
[49]:
C + H2O CO + H2
CO + H2O CO2 + H2
These reactions are supported by the hot spot tem-
perature increase in the micro contact due to exo-
thermal reaction from Sb2O3 to Sb2O4.
Picture 6-3 atom model of Sb2O4 Cervantit
The extreme low friction and wear coefficient that
were achieved are based on a favourable combina-
tion of each single analysed reaction.
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7 Wear Life Prediction
The previous elaborated tribological data represent
the base in order to answer the question, if a dry
running steam engine is possible from the tribologi-
cal point of view. The theoretical life time predic-tion was carried out for the tribological system
piston ring/ cylinder [Picture 8-9] in accordance to
a state of the art steam engine [50,53]. The life-time
was predicted using the specific (Typical) engine
loads and in comparison to the maximum allowable
frictional power loss based on the previously meas-
ured wear rates in the low-wear regime. The basic
methodology is published in [51].
7.1 Determination of the Material SpecificFrictional Power Loss
The characteristic of the applied test geometry is,
that due to the point contact, the wear starts at
“high” contact pressures (PH < 135 MPa), which
decreases with increasing wear scar diameter. Since
the test equipment measures the total wear length of
both samples, the wear rate can be correlated to the
contact pressure at any test time. Diagram 8-9
shows the transition from severe to mild wear and
the resulting critical geometric contact pressure for
this set of test parameters. Based on this diagram
the allowable frictional power loss [PxVxµ; P=geometric contact pressure, V= sliding velocity and
µ = coefficient of friction] were calculated on Table
8-3.
7.2 Specific Engine Loads
For practical application, the critical contact pres-
sure and resulting frictional power loss of the mate-
rial couple have to be below the current engine
loads to ensure always low wear rates. Exemplary
engine loads were calculated with following as-
sumptions:
Temperature of 400°C, injection pressure of the
steam of 5,0 MPa with an expansion to e.g. 1,2
MPa. sliding speed of 3 m/s and minimum life time
of 10,000 h.
The upper first piston ring was considered as the
highly loaded component, but also including the
second piston ring and the carbon piston itself in
the predictions.
On the basis of a typical carbon piston ring dimen-
sions [height=5 mm; thickness= 8 mm; =160
mm] with an allowable loss of radial thickness t=3
mm the wear coefficient has to be in the range of
110-8
mm³/Nm to achieve a life time of approx.
10,000h.
The frictional power loss (Diagram 8-9) can be
calculated using the steam pressure versus crank
angle resulting with the geometric data in a function
of normal force for each tribosystem versus crankangle and the sliding speed versus crank angle.
The ultra low wear coefficient (for dry running!)
coming out from the tribological analysis could
only me matched in the tribometer investigation
from the couple MgO-ZrO2/ EK3245 and nearly
with Al2O3/ EK3245 after running-in (in the low-
wear regime!) as shown in Diagram 8-9.
The outcome of the values in table 8-3 is that the
frictional load in the engine has to be below 0,8
W/mm² for MgO-ZrO2/ EK3245 and below 0,25 for
Al2O3/ EK3245. Diagram 8-10 is showing the re-quired maximum frictional load under above men-
tioned conditions.
Comparing to Table 8-3 these material couples are
able to meet the criteria for a low wear rate in the
mentioned steam engine applications.
Leaving out the running-in wear from the wear
rates given in chapter 4 lead to differential wear
rates of 1,1210-8
mm³/Nm for MgO-ZrO2/ EK3245
and 3,4510-8
mm³/Nm for Al2O3/ EK3245.
This notable comparison does not substitute engine
tests, but predicts a high potential for a reasonable
integration of these material couples in the steam
engines without a liquid or gas phase lubrication
[52].
8 Acknowledgements
The authors would like to take this opportunity to
thanks Mr. J. Schwenzien for the profile and sur-face measurement, Mrs. S. Binkowski and Mrs. R.
Pahl for the microscopy and test body preparation.
Furthermore the authors would like to say thank
you to Dr. K. Witke for Laser Raman investigation.
Thanks are also addressed to Mr. D. Treu for the
Small-Spot-ESCA-Measurements and to Dr. T.
Schneider for the AFM-profilometry.
The experimental works was in part financially sup-
ported by Ingenieurgesellschaft Auto und Verkehr
(IAV GmbH, D-10587 Berlin) in the frame of the
“Zero Emission Engine” [53]. The application of
this work is in part now continued by Enginion AG,
D-13355 Berlin.
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Parameter Couples and Test Conditions
DiskAl2O3
[A19999.7]MgO-ZrO2
[ZN 40]SSi3 N4
[ND 200]SSiC
[EkaSiC D]WC-6Ni
[C7P](Ti,Mo)(C,N)
[TM 10]]Stahl 1.4876
PinEK 32451
antimonyimpregnated
EK 32051
antimonyimpregnated
R 77101
Kunstharzimpregnated
FH 82A2
antimonyimpregnated
FU 24512
Mesophase
ISO 883
Mesophase
ZXF-5Q4
Mesophase
roughness [µm] rotating
disk0,01 0,06 0,15 0,2 0,35 0,5 -
manufacturing polished lappedgrinded
[radial]
grinded
[axial]Pen shoot lapped - lapped -
Sliding speed [m/s] 1 2 3 4 5 - -
temperature [°C] 20 100 200 300 400 450 500
ambiente H2O- liquidH2O steam
100% rel. H.
air
50% rel. H.
UHV
210-3Pa- - -
Table 8-1 test parameter at 20,000m sliding distance and 10 N normal force1 Fa. SGL Carbon,
2 Fa. Schunk,
3 Fa. MGG/ Toyo Tanso,
4 Fa. Poco
Picture 8-1 Thermography of the couple EK3245 /MgO-ZrO2 under dry conditions at 22 °C, v= 3 m/s,
Fn= 10 N and s= 17.000 m
Picture 8-2 Morphology of the wear track EK3245 / Al2O3, 400°C, H2O steam, v=3m/s, Fn= 10 N
and s= 20.000 m
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Picture 8-3 Morphology of the wear track ISO 88 /SSiC, 400°C, H2O steam, v=3m/s, Fn= 10 N
and s= 20.000 m
0
0,01
0,02
0,03
0,04
0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
sliding distance s [m]
C o e f f i c i e n t o f f r i c t i o n µ
F N =10 N
v =3 m/s
t = 400°C
s = 20000 m
steam
Disk:MgO-ZrO2 / Al2O3
Ball: EK3245
EK3245 / MgO-ZrO2
EK3245 / Al2O3
Diagram 8-1 solid-state coefficient of friction as function of sliding distance of antimony impregnated
graphite against Oxide ceramic at 400°C
Picture 8-4 Morphology of the wear track EK3245 / MgO-ZrO2 400°C, H2O steam, v=3m/s, Fn= 10 N
and s= 20.000 m
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Picture 8-5 Morphology of the wear track on MgO-ZrO2 ceramic with the graphite:
left , a) ISO 88 right, b) EK 3245
Number. 1 2 3 4 5 6 7 8 9
manufacturing /
grain size
polished
1µm
polished
3µm
polished
6µm
polished
9µm
polished
15µm
polished
15µm
lapped
20 µm
lapped 50
µm
lapped
80 µm
Roughness R pk [µm] 0,007 0,010 0,011 0,021 0,033 0,035 0,029 0,046 0,183
Coefficient of wear
K v [mm³/Nm]1,34 10-7 6,01 10-8 3,27 10-8 8,01 10-8 1,01 10-7 1,52 10-7 1,29 10-7 1,44 10-7 5,08 10-7
Friction coefficient µ 0,02 0,01 0,008 0,03 0,02 0,04 0,03 0,02 0,01
Table 8-2 Friction coefficient and coefficient of wear of EK3245 as a function of the roughness andmanufacturing of MgO-ZrO2 at 400°C H2O-steam
0
0,01
0,02
0,03
0,04
0,05
0,06
0,07
0,08
1 2 3 4 5
sliding velocity s [m/s]
C o e f f i c i e n
t o f f r i c t i o n µ
F N =10 N
t = 400 °C
s = 20000 m
steam
Disk: MgO-ZrO2
Ball: Carbon EK 3245
Diagram 8-2 Coefficient of friction of MgO-ZrO2/EK3245 as a function of the sliding speed at aroughness of R pk 0,01 µm
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1,00E-08
2,10E-07
4,10E-07
6,10E-07
8,10E-07
1,01E-06
1,21E-06
1,41E-06
1,61E-06
W e a r C o e f f i c i e n t B a l l [ m m ³ / N
m ]
100 200 300 400 450 500
Temperature T [°C]
dry air
steam
F N =10 N
v =3 m/s
s = 20000 m
Disk: MgO-ZrO2
Ball: Carbon EK3245
Diagram 8-3 wear coefficient of MgO-ZrO2 as a function of the environment under dry friction with and
without steam
0
5000
10000
15000
20000
25000
30000
1100 1200 1300 1400 1500 1600 1700 1800
wave lenght cm-1
I n t e n s i y
0
500
1000
1500
2000
2500
3000
3500
wear track
pore
Diagram 8-4: Laser- Raman peaks on MgO-ZrO2 into the wear track and pore
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0
5000
10000
15000
20000
25000
30000
1100 1200 1300 1400 1500 1600 1700 1800
wave lenght cm-1
I n t e n s i t y
wear track
pore
Diagram 8-5: Laser Raman peaks on MgO-ZrO2 wear track and into pore
Picture 8-6: Topography of the wear track MgO-ZrO2/EK3245 at T= 400 °C H2O-steam
Picture 8-7: Profile measurement on the wear track of MgO-ZrO2/EK3245 at T= 400 °C H2O-steam
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Diagram 8-6 Binding energy of Zr after testing
Used at 400 °C, steamed, offset +2,22
Diagram 8-7 Binding energy of Zr(OH)4
Reference powder, offset +0,00
Diagram 8-8 Binding energy of Sb after testing at 400 °C, steamed, offset +2,22
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Picture 8-8 Structure of Bayerit and Gibbsit as Hydroxide or Hydrate of Aluminum oxide
Picture 8-9 typical piston/ cylinder arrangement of steam engines
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0
0,005
0,01
0,015
0,02
0,025
0,03
0,035
0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
sliding distance s [m]
l i n e a r W e a r R a t e W l [ m m ]
FN =10 N
v =3 m/s
t = 400°C
s = 20000 m
H2O steam
Disk: MgO-ZrO2 / Al2O3
Pin: EK3245 Al2O3
MgO-ZrO2
Pcritical=8,32 N/mm²
Pcritical=28,29
Diagram 8-9 linear wear as a function of sliding distance of MgO-ZrO2 and Al2O3 mated with EK3245
Materi al cou-pl es
Pcr [N/ mm²]
v[m/ s]
µ P v µ[W/ mm²]
Al 2O3/ EK3245 8, 32 3 0, 01 0, 25MgO- ZrO
2/ EK3245 28, 29 3 0, 01 0, 8
Table 8-3 calculated frictional power loss with a friction coefficient of µ=0,01
Friction power loss for µ= 0,01
0,00
0,05
0,10
0,15
0,20
0,25
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360
Crankshaft Angle
p x v x µ [ W / m m ² ]
Piston
1. Pistonring
2. Pistonring
Diagram 8-10 Frictional power load/loss as a function of crankshaft angle
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