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Friction and wear properties of hard carbon coatings at high sliding speed
WEAR EUEVIER
Wear203-204 ( 1997)442446
Friction and wear properties of hard carbon coatings at high sliding speed T. Le Huu, H. Zaidi, D. Paulmier
Abstract The frictmn and wear behavioun of hard carbon coatings have been studied mainly at low sliding speed. ‘Ilk
paper presents a sNdy at
high shdmg speed (30-35 m s- ’). Various types of hard carbon coatings were deposited on stainlesssteel (304L) pins. These coatings are produced by p!asma-asslsted chemical vapour deposition processesunder different deposition conditions. The surface properties and morphology of the coatings have been characterisedby surface analysis methods such as scanning electron microscopy and Ramao spectrometry. The coated pins slide against a steel XC30 rotating disc. The hardnessof disc after heat treatment is 5 GPa. The experimental results show that these coatings exhibit very low friction coefficients and high wear resistances.This behaviow of hard carbon coatings can be explained bj the s~multanews presenceof the sp’ and sp’ bonds hybridisation, by the ca&wn-hydrogen clusters on the surface of these films, and by hydrogen desorbing from tbe hard carbon films during friction inducing their reconstruction or creating on them double (n, sp*) bonds.
relatively high wear rate, and under other conditions they exhibited a relative high friction coefficient but a low wear rate. These results can be explained by desorption of hydrogen during friction in vacuum, which leads to a low friction coefficient of the films [9]. Thts IS cotnctdent wtth the mvesligation of Piekarcxyk [ IO] on the transformation of spa to sp* or T bonds during heating in vacuum. The objective of this study is to investigate the effect of the temperature produced by friction at high sliding speed on the friction and wear behaviourof hard carbon films in ambient atmosphere.
2. Experimental procedures 2.1. Preparation
and coaring deposition
We have obtained hard carbon coatings on stainless steel 304Lpinsubstrates withplasma-assistedchemicalvapordep osition (CVD). Before the deposition, the stainless steel pin substrate was polished with 3 Pm and then I pm diamond powder. This technique produces a high and uniform nucleation density 11). The apparatus and process details to obtain hard carbon coatings are reported elsewhere [ 121. substrate sample was immersed in a mixture of acetylene and hydrogen plasma. The acetylene/hydrogen ratio was coutrolled wtth electronic mass flow controilers. The total pressure m the chamber was kept close to 500 Pa. Different
[
The
7’ Le Huu et al / Wear203-204
(1997) 442446
% f
2.3. Contact temperature measurement
d The real contact temperature is very difficult to measure because nothing may be inserted in the contact area. Mean contact temperature is measured by a thermocouple fitted in mm from the contact. It is assum& that the the pin at temperature measured there is not significantly different from the contact temperature.
I
F;g 1
z
200 seem H,, 2 seem C*H,and wah a substratetemperarun?of T.-700°C. 3. Results and discussion 3.1. Scanning electron microscopy ad
Raman
spectrometry analysis
I
Fig. (a) shows a scanning electron microscopy ( SEM) photograph of films grown in 200 standard cm’ min-’ (seem) Hz, 2 seem ( IC ) &Hz and with a substrate temperature T, = 700 “C. The film consist of very fine crystal in a spherical clusters. The crystal size ranges between 0.5 pm and 0.6 pm. SEM analysis of films grown in 200 seem Hz. 2 seem ( 1% ) &HZ and at a substrate temperature of T, =900 “C (Fig. 2(a) ) shows that the BLC films have nodule sizes rangtng between 2 and 2.5 pm.
operated in the multichannel mode with the beam focused to a spot diameter of approximately 2 urn. Raman spectra on fine crystal size and nodule size of hard carbon films are respectively shown in Fig. Ifb) and Fig. 2(b) The sharp peaks due to diamond 1334 cm-’ in both spectra Very broad weak around l5@J cm-’ and l@lO cm-’ castling to amorphous carbon 131 are also detected in both of them. The intensity of the peaks due to amorphous carbon is hirers that of diamond. Prawer and Nugent [ 141 have shows that films with sp2 content between 20% and 40% give Raman peak positions in the range of 1565-1570 cm-‘. However. the sensitivity of the Raman technique to the sp’ bonds phase of carbon is about 50 times greater than that of the sp3 diamond bonds phase 151. hard carbon films used in this study contained about 30% sp* for the fine crystal films and 40% sp’ for me nodule size films.
[
[
Thus, the
3.2. Raman analysis 3.3. Friction characteristics Raman spectra were recorded using an argon ton laser Raman microprobe. The exciting laser wavelength is 514.5 nm with a laser power of 20-30 mW. The instrument was
Fig. 3 shows the evolution, in ambient aonospbere, oftbe friction coefficient of both hard carbon films against a steel
T. LC Huu ct al. /Wear 203-204 (195’7) 442-446
Then it slowly decreases to u=O.O6 in the course of friction and stab&es at this value. about 40% sp*. the friction coefficient is relatively high, p = 0.18. at lirst then it gradually decreases to p= 0.09 and is stable at this value.
??For the films containing
3.4. Wear characteristics The effect of the sliding distance on the wear tates of the hard carbon-coated pins was studied. Fig. 4 shows tbat the wear rates of both films depend of sliding distance. Wear rates decmase when the slidina distance increases. At a normal load of 5 N and a sliding contact of V= 30 m s-r. the wear rates W of the coated pin decrease from W=OS 10M6 mm3 N-’ m-’ to W=O.42 10e6 mm3 N-’ m-r when the sliding distance increases from 18840 m to 37680 m for films containing 40% sp’ bonds and from W=OSO 10e6 mm3 N-’ m-’ to W-O.38 10m6 nun3 N-’ m - for films containing about 30% so’ bonds. Fig. 5 shows the mek contact tekueratme evolution at high&ding speed. It increases with increasing friction time. and is about 285 “C after 15 min of sliding. The difference of temnerature measured between oin and disc can be caused by factors such as geometry. hea; conduction of the material and heat prcduccd by friction.
’
0
Qzo aaaa a * ooo ooo’aa Ql
00
0.10
i
aas
F=ovststti~
0 00 .e~~0000000 .**eee*
a had carbn-ccatcd pin .5 N, sliig speed. 30 m
dwz. This is reccxded versus the sliding distance at high slidrngspeed(XL35ms-‘). For the films containing about 30% sp’, the friction coefficient ts high ( y = 0.2) in t period (about 12.oo m &ding datance) and s decEzses to p=o.12.
T. L.? Hw et al. /Wear 203-2&d (1997) 442446
3.5. Microscopicobservntionof thefiction track For the steel disc a thick oxide layer of disc material was formed on the surface of friction track. This layer was usually dense, and the. thickness incrcascd with increasing sliding
445
region. This decmases the coefficient of tiiction the friction track from abrasion.
285 “C. But the flash temperature
cr
Speed.
For the coated pins a thick layer of material, probably graphite., transformed frrJ?F. !EZ! Z&XZ by %CAh was observed on the surface of the friction track.
4. Discussion The exceptional triboiogical and wear properties of these films can be explained by the simultaneous presence of sp’ and spz bonds. For the case of hard carbon films, material composed of a mixture of sp3 and sp’ bonds and a high
percentage of hydrogen(40%atvohutte)[ 161,the hydrogen incorporated on thehardcarbonfilmsis unstableunderhigh vacuumconditions[ 171 andit canbe desorbedat low temperatureduringfrictiontests [ 181.But these bonds are very stable and inert under ambient atmosphere. The strucNre and the in the film strongly affect the friction and wear behaviour, as well as the lifetime of hard carbon films. The sp* phase with the. presence of hydrogen in the film lubricates the contact under vacuum and the rigid s$ phase inhibits abrasive wear. The critical temperature T, of phase transition from hydrogenated hard carbon films to dehydro genatcdfilms, ~haracteriztdbythe.desorption ofthehydrogenterminated surface, depends on the density of hydrogen-terminated bonds in the surface, on the environment and on the Hertzian contact pressure. T, is about 180°C in vacuum [9] and higher than that in air. As is well know, in ambient atmosphere hydrogen atoms are bonded to carbon atoms on the. surface of hard carbon films by an extremely strong covalent bond. At low sliding speed, the temperature increase produced by friction in the contact zone is low. It is not high enough to induce hydrogen &sorption and the friction behaviour of the friction couple is essentially detetmincd by deformation processes. Increasing of the sliding speed or sliding distance leads to increasing flash temperature at the contact asperities. That exacerbates the local chemical reactions and thus the dcsorption of hydrogen may occur in ambient atmosphere. For both filmsthatleadsto a significant reductionin the friction cocfticient at high sliding speed. The fine crystal films have a much higher number of contacting asperities. This reduces the contact pressure at the asperity tips, and leads to lower friction coefficient for the fine crystal films. The friction coefficient is p = 3.2 at low sliding speed and it is reduced to /~=0.06 at high sliding speed for fine crystal films and from /.r = 0. I8 to p = 0.09 for nodule size films. For the steel XC30 disc, a thick layer of material growth on the friction track was observed. This layer is harder than the metal it covers and behaves lie a lubricant in the contact
sp3/sp* ratio
the environment It is close to 4OO’C for diamond-like films high vacuum conditions [IO] any graphite created on the rubbing s lubrication of the sliding contact. According to Ronkainen et al. [ 191
couple (hardcarbon-coated disc/steel faceswere.analysedby secondaryionm Auger spectroscopy. The analyses revealed that the thick tribolayer formed on the pin wear surface mainly consisted of oxides of pin material. A layer of carbon i&lure frictiontrackofhardcarbonfihnswhen higb &ding speeds were applied. Gardos and Soriano [I ] have also mported that at high temperature, reconstruction and grapbitization of the diamond surface may occur and that the. friction cocfgcient is lower than that obtained The friction and wear in ambient atmosphere is neous presence of the sp’ and spz bonds in the iibns. The rigidity of the sp’ phase limits deep penetration in the sliiing contact, decreases the affected contact zone and reduces tbc motion energy during friction. Cleavage and softness of the sp* phase lubricates the sliding contact
5. Conclmaion
In the present study, at high sliding speeds 35 m s- ’ in ambient atmosphere we have demons 0 the friction coefficient is about p=O.O6 for line crystal films and p = 0.09 for nodule seze films; 0 wear rate is about W=O.38 10e6 mm3 N-’ in-’ for tine grain and W=O.42 10-6mm3 N-’ m-’ for coarse grain hard carbon films. o The temperature increase produced by friction in tire contact zone is high, about 285 “C to the sp* phase occurs at tbis consumes a I and creates a To conclude friction couples in high sliding speed rotor ~bj~.
203-204 (1997) 442446
1101W. Piekarczyk.1. CrysralGrmvrh,119( 1992) 345-362.
R&e
IIll
(I1)(19%-l) 2599.
[I ] MN Gardos and BL. Smw0.l PAotcrRes..5 [2] I(. Miy&. Swj Cm%Tcrlutal... 44 ( 1990) 227 (31 B.R.Stoner.G.H.t.4.IMaS.D Wollcac16T.GIa~.Phys (1992) II067
Rcv.B.45
.n,
[5] 7’.Le Huu.H. Nay. H. Z&ii andD. Wulmier.DiammrdRclar.Mawr. (1994) 1028. [6] R. Mamung. HJ. T&e and PE. Wiireoga Thin Solid Fdms. I43 (1%6!3l. 17) RicbrdLC. WuK.~iyoshi.S.~y~.HE.JxLson.G.Choo.A.L and P.N. Barna. Diamond Film Koaeoyt-both.A. C 7ec/moL.3(1) (1993) 17-29. [S] SJ. Bull. P.R. Chalker.C. Johnsmuand V. Mawe. Surf CwnnS TccivwL.-9 (1994) 603-610 19: T Le Huu H. Zai& and D. w&r. Wear, 181-183 (1995) 766-
3
no
Y. Bomouh, ML. II&ye. A. D&b&Akiani. A. Mmlmvs. J. Cnnogora J.L. Fave. C. Colliex. A. Glwnr&iu and C. S&dmawl. DiamondR&red Mater.. 2 ( 1993) 259. D Rulmi~.H.Zaidi.H.Ne~.T.LeHuuandT.MachiaSu~ Tcchnol .62 ! !993! 57”.
Coafinf
Y TzenS.M Ymhitaw. M. M*m&aw a%!A. Fe:dinan.Maw. SCI. Mmwgraplu.73 (1991) 431-438. S. Rawer andK.W. Nugcnr.LXam.md RelatedMater.. 2 ( 1993) 753. N. WadaandS.A. Solin..PhysicaB&C. lO5B ( 1981) 353. VG. Raklmko. T.\’ Konmenko.T. Foursovaand E.N. Laubnii. DiamondRelartdMawr.. 2 (1993) 21 I-217. T. Le Huu.H. Zaidi aad D. Paulmier.Wear. 181-183 (1995) 766-
no. D. F’aulmier,H. zaidi. T. Le Huuand A.M. Dwand. DiamondFifm Technoi..4 (3) (19%) 167-179. H. Rmkainea.1. Like. 1. Koskinenacd S. Varjw, Su$ Coming Techno/.. 54/55( 1992) 570.
Wear203-204 ( 1997)442446
Friction and wear properties of hard carbon coatings at high sliding speed T. Le Huu, H. Zaidi, D. Paulmier
Abstract The frictmn and wear behavioun of hard carbon coatings have been studied mainly at low sliding speed. ‘Ilk
paper presents a sNdy at
high shdmg speed (30-35 m s- ’). Various types of hard carbon coatings were deposited on stainlesssteel (304L) pins. These coatings are produced by p!asma-asslsted chemical vapour deposition processesunder different deposition conditions. The surface properties and morphology of the coatings have been characterisedby surface analysis methods such as scanning electron microscopy and Ramao spectrometry. The coated pins slide against a steel XC30 rotating disc. The hardnessof disc after heat treatment is 5 GPa. The experimental results show that these coatings exhibit very low friction coefficients and high wear resistances.This behaviow of hard carbon coatings can be explained bj the s~multanews presenceof the sp’ and sp’ bonds hybridisation, by the ca&wn-hydrogen clusters on the surface of these films, and by hydrogen desorbing from tbe hard carbon films during friction inducing their reconstruction or creating on them double (n, sp*) bonds.
relatively high wear rate, and under other conditions they exhibited a relative high friction coefficient but a low wear rate. These results can be explained by desorption of hydrogen during friction in vacuum, which leads to a low friction coefficient of the films [9]. Thts IS cotnctdent wtth the mvesligation of Piekarcxyk [ IO] on the transformation of spa to sp* or T bonds during heating in vacuum. The objective of this study is to investigate the effect of the temperature produced by friction at high sliding speed on the friction and wear behaviourof hard carbon films in ambient atmosphere.
2. Experimental procedures 2.1. Preparation
and coaring deposition
We have obtained hard carbon coatings on stainless steel 304Lpinsubstrates withplasma-assistedchemicalvapordep osition (CVD). Before the deposition, the stainless steel pin substrate was polished with 3 Pm and then I pm diamond powder. This technique produces a high and uniform nucleation density 11). The apparatus and process details to obtain hard carbon coatings are reported elsewhere [ 121. substrate sample was immersed in a mixture of acetylene and hydrogen plasma. The acetylene/hydrogen ratio was coutrolled wtth electronic mass flow controilers. The total pressure m the chamber was kept close to 500 Pa. Different
[
The
7’ Le Huu et al / Wear203-204
(1997) 442446
% f
2.3. Contact temperature measurement
d The real contact temperature is very difficult to measure because nothing may be inserted in the contact area. Mean contact temperature is measured by a thermocouple fitted in mm from the contact. It is assum& that the the pin at temperature measured there is not significantly different from the contact temperature.
I
F;g 1
z
200 seem H,, 2 seem C*H,and wah a substratetemperarun?of T.-700°C. 3. Results and discussion 3.1. Scanning electron microscopy ad
Raman
spectrometry analysis
I
Fig. (a) shows a scanning electron microscopy ( SEM) photograph of films grown in 200 standard cm’ min-’ (seem) Hz, 2 seem ( IC ) &Hz and with a substrate temperature T, = 700 “C. The film consist of very fine crystal in a spherical clusters. The crystal size ranges between 0.5 pm and 0.6 pm. SEM analysis of films grown in 200 seem Hz. 2 seem ( 1% ) &HZ and at a substrate temperature of T, =900 “C (Fig. 2(a) ) shows that the BLC films have nodule sizes rangtng between 2 and 2.5 pm.
operated in the multichannel mode with the beam focused to a spot diameter of approximately 2 urn. Raman spectra on fine crystal size and nodule size of hard carbon films are respectively shown in Fig. Ifb) and Fig. 2(b) The sharp peaks due to diamond 1334 cm-’ in both spectra Very broad weak around l5@J cm-’ and l@lO cm-’ castling to amorphous carbon 131 are also detected in both of them. The intensity of the peaks due to amorphous carbon is hirers that of diamond. Prawer and Nugent [ 141 have shows that films with sp2 content between 20% and 40% give Raman peak positions in the range of 1565-1570 cm-‘. However. the sensitivity of the Raman technique to the sp’ bonds phase of carbon is about 50 times greater than that of the sp3 diamond bonds phase 151. hard carbon films used in this study contained about 30% sp* for the fine crystal films and 40% sp’ for me nodule size films.
[
[
Thus, the
3.2. Raman analysis 3.3. Friction characteristics Raman spectra were recorded using an argon ton laser Raman microprobe. The exciting laser wavelength is 514.5 nm with a laser power of 20-30 mW. The instrument was
Fig. 3 shows the evolution, in ambient aonospbere, oftbe friction coefficient of both hard carbon films against a steel
T. LC Huu ct al. /Wear 203-204 (195’7) 442-446
Then it slowly decreases to u=O.O6 in the course of friction and stab&es at this value. about 40% sp*. the friction coefficient is relatively high, p = 0.18. at lirst then it gradually decreases to p= 0.09 and is stable at this value.
??For the films containing
3.4. Wear characteristics The effect of the sliding distance on the wear tates of the hard carbon-coated pins was studied. Fig. 4 shows tbat the wear rates of both films depend of sliding distance. Wear rates decmase when the slidina distance increases. At a normal load of 5 N and a sliding contact of V= 30 m s-r. the wear rates W of the coated pin decrease from W=OS 10M6 mm3 N-’ m-’ to W=O.42 10e6 mm3 N-’ m-r when the sliding distance increases from 18840 m to 37680 m for films containing 40% sp’ bonds and from W=OSO 10e6 mm3 N-’ m-’ to W-O.38 10m6 nun3 N-’ m - for films containing about 30% so’ bonds. Fig. 5 shows the mek contact tekueratme evolution at high&ding speed. It increases with increasing friction time. and is about 285 “C after 15 min of sliding. The difference of temnerature measured between oin and disc can be caused by factors such as geometry. hea; conduction of the material and heat prcduccd by friction.
’
0
Qzo aaaa a * ooo ooo’aa Ql
00
0.10
i
aas
F=ovststti~
0 00 .e~~0000000 .**eee*
a had carbn-ccatcd pin .5 N, sliig speed. 30 m
dwz. This is reccxded versus the sliding distance at high slidrngspeed(XL35ms-‘). For the films containing about 30% sp’, the friction coefficient ts high ( y = 0.2) in t period (about 12.oo m &ding datance) and s decEzses to p=o.12.
T. L.? Hw et al. /Wear 203-2&d (1997) 442446
3.5. Microscopicobservntionof thefiction track For the steel disc a thick oxide layer of disc material was formed on the surface of friction track. This layer was usually dense, and the. thickness incrcascd with increasing sliding
445
region. This decmases the coefficient of tiiction the friction track from abrasion.
285 “C. But the flash temperature
cr
Speed.
For the coated pins a thick layer of material, probably graphite., transformed frrJ?F. !EZ! Z&XZ by %CAh was observed on the surface of the friction track.
4. Discussion The exceptional triboiogical and wear properties of these films can be explained by the simultaneous presence of sp’ and spz bonds. For the case of hard carbon films, material composed of a mixture of sp3 and sp’ bonds and a high
percentage of hydrogen(40%atvohutte)[ 161,the hydrogen incorporated on thehardcarbonfilmsis unstableunderhigh vacuumconditions[ 171 andit canbe desorbedat low temperatureduringfrictiontests [ 181.But these bonds are very stable and inert under ambient atmosphere. The strucNre and the in the film strongly affect the friction and wear behaviour, as well as the lifetime of hard carbon films. The sp* phase with the. presence of hydrogen in the film lubricates the contact under vacuum and the rigid s$ phase inhibits abrasive wear. The critical temperature T, of phase transition from hydrogenated hard carbon films to dehydro genatcdfilms, ~haracteriztdbythe.desorption ofthehydrogenterminated surface, depends on the density of hydrogen-terminated bonds in the surface, on the environment and on the Hertzian contact pressure. T, is about 180°C in vacuum [9] and higher than that in air. As is well know, in ambient atmosphere hydrogen atoms are bonded to carbon atoms on the. surface of hard carbon films by an extremely strong covalent bond. At low sliding speed, the temperature increase produced by friction in the contact zone is low. It is not high enough to induce hydrogen &sorption and the friction behaviour of the friction couple is essentially detetmincd by deformation processes. Increasing of the sliding speed or sliding distance leads to increasing flash temperature at the contact asperities. That exacerbates the local chemical reactions and thus the dcsorption of hydrogen may occur in ambient atmosphere. For both filmsthatleadsto a significant reductionin the friction cocfticient at high sliding speed. The fine crystal films have a much higher number of contacting asperities. This reduces the contact pressure at the asperity tips, and leads to lower friction coefficient for the fine crystal films. The friction coefficient is p = 3.2 at low sliding speed and it is reduced to /~=0.06 at high sliding speed for fine crystal films and from /.r = 0. I8 to p = 0.09 for nodule size films. For the steel XC30 disc, a thick layer of material growth on the friction track was observed. This layer is harder than the metal it covers and behaves lie a lubricant in the contact
sp3/sp* ratio
the environment It is close to 4OO’C for diamond-like films high vacuum conditions [IO] any graphite created on the rubbing s lubrication of the sliding contact. According to Ronkainen et al. [ 191
couple (hardcarbon-coated disc/steel faceswere.analysedby secondaryionm Auger spectroscopy. The analyses revealed that the thick tribolayer formed on the pin wear surface mainly consisted of oxides of pin material. A layer of carbon i&lure frictiontrackofhardcarbonfihnswhen higb &ding speeds were applied. Gardos and Soriano [I ] have also mported that at high temperature, reconstruction and grapbitization of the diamond surface may occur and that the. friction cocfgcient is lower than that obtained The friction and wear in ambient atmosphere is neous presence of the sp’ and spz bonds in the iibns. The rigidity of the sp’ phase limits deep penetration in the sliiing contact, decreases the affected contact zone and reduces tbc motion energy during friction. Cleavage and softness of the sp* phase lubricates the sliding contact
5. Conclmaion
In the present study, at high sliding speeds 35 m s- ’ in ambient atmosphere we have demons 0 the friction coefficient is about p=O.O6 for line crystal films and p = 0.09 for nodule seze films; 0 wear rate is about W=O.38 10e6 mm3 N-’ in-’ for tine grain and W=O.42 10-6mm3 N-’ m-’ for coarse grain hard carbon films. o The temperature increase produced by friction in tire contact zone is high, about 285 “C to the sp* phase occurs at tbis consumes a I and creates a To conclude friction couples in high sliding speed rotor ~bj~.
203-204 (1997) 442446
1101W. Piekarczyk.1. CrysralGrmvrh,119( 1992) 345-362.
R&e
IIll
(I1)(19%-l) 2599.
[I ] MN Gardos and BL. Smw0.l PAotcrRes..5 [2] I(. Miy&. Swj Cm%Tcrlutal... 44 ( 1990) 227 (31 B.R.Stoner.G.H.t.4.IMaS.D Wollcac16T.GIa~.Phys (1992) II067
Rcv.B.45
.n,
[5] 7’.Le Huu.H. Nay. H. Z&ii andD. Wulmier.DiammrdRclar.Mawr. (1994) 1028. [6] R. Mamung. HJ. T&e and PE. Wiireoga Thin Solid Fdms. I43 (1%6!3l. 17) RicbrdLC. WuK.~iyoshi.S.~y~.HE.JxLson.G.Choo.A.L and P.N. Barna. Diamond Film Koaeoyt-both.A. C 7ec/moL.3(1) (1993) 17-29. [S] SJ. Bull. P.R. Chalker.C. Johnsmuand V. Mawe. Surf CwnnS TccivwL.-9 (1994) 603-610 19: T Le Huu H. Zai& and D. w&r. Wear, 181-183 (1995) 766-
3
no
Y. Bomouh, ML. II&ye. A. D&b&Akiani. A. Mmlmvs. J. Cnnogora J.L. Fave. C. Colliex. A. Glwnr&iu and C. S&dmawl. DiamondR&red Mater.. 2 ( 1993) 259. D Rulmi~.H.Zaidi.H.Ne~.T.LeHuuandT.MachiaSu~ Tcchnol .62 ! !993! 57”.
Coafinf
Y TzenS.M Ymhitaw. M. M*m&aw a%!A. Fe:dinan.Maw. SCI. Mmwgraplu.73 (1991) 431-438. S. Rawer andK.W. Nugcnr.LXam.md RelatedMater.. 2 ( 1993) 753. N. WadaandS.A. Solin..PhysicaB&C. lO5B ( 1981) 353. VG. Raklmko. T.\’ Konmenko.T. Foursovaand E.N. Laubnii. DiamondRelartdMawr.. 2 (1993) 21 I-217. T. Le Huu.H. Zaidi aad D. Paulmier.Wear. 181-183 (1995) 766-
no. D. F’aulmier,H. zaidi. T. Le Huuand A.M. Dwand. DiamondFifm Technoi..4 (3) (19%) 167-179. H. Rmkainea.1. Like. 1. Koskinenacd S. Varjw, Su$ Coming Techno/.. 54/55( 1992) 570.