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Friction Behavior of DLC filmFriction Behavior of DLC filmwith Environmental Changeswith Environmental Changes
Copyright, 1997 © Dale Carnegie & Associates, Inc.
S. J. Park*, K.-R. Lee*, D.-H. Ko+, K. Y. Eun** Korea Institute of Science & Tech.
Future Technol. Research Division
+ Yonsei University Dept. of Ceramic Eng.
Frictional Properties of Hard Coating Films
DLC
WC
TiN
CrN
TiCN
Wear Rate Friction Coefficient
2.0 1.6 1.2 0.8 0.4 0.2 0.4 0.6 0.8 1.0Relative value
Various Applications of DLCVarious Applications of DLC
Disadvantages of Pure DLC Film
• High internal compressive stresses(~ 9 GPa)
result in poor adhesion.
• The friction behavior depends on
environment
(especially dependent on humidity)
Previous Works
• K. Y. Eun et al, Surf. Coat. Technol. 86-87 (1996) 569
– High and unstable friction coefficient of DLC films in vacuum
– Formation of roll-shaped polymeric debris in vacuum
• S. H. Yang et al, Wear 252 (2001) 70– Increase of friction coefficient with the increase of humidity
– Agglomeration of small debris
Purposes of This Work
• To test the friction behavior of DLC film in various environment environment, especially such as humidity
• To find the reason of dependence of humidity in DLC films in the point of tribochemical reaction
Deposition Condition
• RF PACVD(13.56 MHz)
• Precursor Gas : C6H6, C6H6 + SiH4,
• Deposition Pressure : 1.33 Pa
• Bias Voltage : - 400 Vb
Substrate : P-type (100) Si-wafer
• Film thickness : 1 ㎛
• Si concentration : 2 at.%
Friction Test Condition
Motor
Constant
Temperature and
Humidifier
Rotary Pump
Ball : AISI 52100 Steel Ball, Al2O3
Normal Load : 4 N
Speed : 220 rpm
Temperature : Room temperature
Environment Gas
Atmosphere
(relative humidity : 0 – 90 %)
Ultra high purity oxygen
Normal
Load
Film
Friction Coefficient of DLC FilmFriction Coefficient of DLC Film
a-C:H Si-C:H
Images of Ball Scar (a-C:H)
• RH : 90 %• RH : 0 % • RH : 50 %
100 ㎛ 100 ㎛ 100 ㎛
Wear Rate of Track and Ball
Track
Ball
• a-C:H • Si-C:H
Relationship between Friction Coefficient and Ball Wear Rate
Friction Behavior with Environment
• RH : 50 %
Ball
a-C:H
• RH : 0 % • RH : 90 %
Ball
a-C:H
C-O-Fe C-O
Ball
a-C:H Fe-O
AES Spectra of Track Debris (a-C:H)
a-C:H
a-C:H
a-C:H
FeFe-O
FeFe-O
FeFe-O
Friction Coefficient in Oxygen Environment
Wear Rate of Track and Ball (O2 Env.)
Track
Ball
• a-C:H • Si-C:H
AES Sepectra of Track (O2 Env.)
a-C:H
a-C:H
Si-C:H
Fe
Al2O3
Fe
Fe-O
Fe-O
a-C:H
Conclusions
The increase of friction coefficient with the increase of humidity depends on the oxidation of steel ball
Iron rich debris by oxidation of steel ball plays key role of the
increase of friction coefficient
Friction coefficient of Si-C:H film is low and stable in oxygen environment
Silicon rich debris by severe wear of film decreases the friction
coefficient
G-peak Position of the Film and Scar(a-C:H)
Photograph of Wear Track (a-C:H)
• RH : 90 %• RH : 0 % • RH : 50 %
Photograph of Wear Track (Si-DLC, 2 at.%)
250 ㎛
250 ㎛
• RH : 90 %• RH : 0 % • RH : 50 %
250 ㎛
Photograph of Track and Ball (O2 Env.)
Track
Si-C:H With Steel Ball
Ball
a-C:H With Steel Ball
a-C:H With Al2O3 ball
100 ㎛
100 ㎛
100 ㎛
250 ㎛250 ㎛250 ㎛