Friction Behavior of DLC film with 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 RateFriction Coefficient Relative value

Various 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 (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 : C 6 H 6, C 6 H 6 + SiH 4, Deposition Pressure : 1.33 Pa Bias Voltage : V b 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 Steel Ball, Al 2 O 3  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 Film a-C:H Si-C:H

Images of Ball Scar (a-C:H) RH : 90 % RH : 0 % RH : 50 % 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 Fe Fe-O Fe Fe-O Fe Fe-O

Friction Coefficient in Oxygen Environment

Wear Rate of Track and Ball (O 2 Env.) Track Ball a-C:H Si-C:H

AES Sepectra of Track (O 2 Env.) a-C:H Si-C:H Fe Al 2 O 3 Fe 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 ㎛ RH : 90 % RH : 0 % RH : 50 % 250 ㎛

Photograph of Track and Ball (O 2 Env.) Track Si-C:H With Steel Ball Ball a-C:H With Steel Ball a-C:H With Al 2 O 3 ball 100 ㎛ 250 ㎛