1. DLC DLC 2005 2005 Se Jun Park, Kwang-Ryeol Lee, Seung-Cheol Lee, Future Technology Research Division, Korea Institute of Science and Technology

2. Tribological Properties of Hard Coating Films DLC WC TiN CrN TiCN Wear RateFriction Coefficient 2.01.61.20.80.40.20.40.60.81.0 Relative value

3. Dependence of Tribological Behavior of DLC Films on Humidity R. Gilmore et al Surf. Coat. Technol. 133-134, (2000), 437

4. Previous Works about the Environmental Dependence Y. Kokaku et al. J. Vac. Sci. Technol. A 7 (1989) 2311 High friction coefficient in humid environment An unstable oxide layer on DLC film surface involved in humid environment B. Marchon et al, IEEE Trans. Magn. 26 (1990) 2670 Surface smoothness of DLC film by chemisorbed oxygen The increase of real contact area C. Donnet et al., Tribo. Letters, 4 (1998) 259 Prevention of the growth of the carbonaceous transfer film by the water vapor

5. DLC Counterface Reaction with H 2 O Transfer layer FNFN F Tribology Process of DLC Film in Humid Air

6. DLC Reaction with H 2 O FNFN F Tribology Process of DLC Film in Humid Air Tribo-chemical reaction Transfer layer Material transfer Counterface

7. Friction Coefficient of DLC Film and Counterface RH : 0 % DLC against steel ball RH : 50 % RH : 90 % 2 2 2 + S. J. Park et al, Diam.Rel.Mater., 12 (2003) 1517 S. J. Park et al, Tribol. Intl., 37 (2004) 913

8. Friction Behavior of DLC Using Steel Ball with the Change of Humidity RH : 0 % Low oxidational wear of ball RH : 90 % High oxidational wear of ball Friction coefficient Relative Humidity Formation of Fe-rich debris (Degradation of lubricant properties of DLC film) Increase of the debris size Steel DLC C-O-Fe Fe-oxide C-O Steel DLC

9. Motivations If the formation of Fe-rich debris is suppressed, what will happen? Steel DLC

10. Purposes of the Present Work To characterize the tribological behavior of DLC film with the humidity change in various tribo-system. DLC against steel ball DLC against DLC coated ball To find the reason for the humidity dependence of frictional behavior of DLC film in the view point of tribo-chemical reaction.

11. Deposition Condition RF PACVD(13.56 MHz) Precursor Gas : C 6 H 6 Deposition Pressure : 1.33 Pa Bias Voltage : - 400 V b Substrate : P-type (100) Si-wafer Film Thickness : 1 Residual Stress : 0.9 ± 0.02 GPa Hardness : 11 ± 0.5 GPa

12. Tribo-test Condition Ball-on-disc type tribometer isolated by chamber Counterface : AISI 52100 steel ball DLC coated steel ball Normal Load : 4 N Rotation Speed : 20 cm/s Temperature : Room temperature Test Environment: Ambient atmosphere (Relative humidity : 0 – 90 %) Film Hygrometer Normal Load Loadcell Humidity controller Rotary Pump

13. Friction Coefficient of DLC film with Humidity Change

14. Chemical Composition of Debris with Humidity Change DLC against DLC coated ball

15. Friction Coefficient and Chemical Composition of the Debris

16. Morphology of Debris on Track with Humidity Change RH : 0 %RH : 50 %RH : 90 % 2 2 2 DLC against DLC coated ball

17. Friction Coefficient and Chemical Composition of the Debris

18. Raman Spectra of Transfer Layer DLC Coated Ball Steel Ball

19. Friction Coefficient Vs. Relative Humidity Structure of Transfer Layer and Friction coefficient of Si-DLC film Raman spectra of transfer layer of Si-DLC S. J. Park et al, Tribol. Intl., 37 (2004) 913 Raman spectra of transfer layer of DLC

20. Schematic Diagram of Friction Behavior in Humid Air Formation of large size of debris Formation of Fe-rich debris Formation of graphitic transfer layer Incorporation of Fe itself Absence of Fe in debris Formation of diamond-like structure of transfer layer DLC Steel DLC DLC Coated Ball Steel Ball

21. Which is the major Contribution of Fe incorporation? Fe-rich debris RH : 90 % RH : 0 % Graphitic transfer layer that is sensitive to humidity Incorporated Fe in debris itself Abrupt change of humidity Steel Abrupt change of humidity during tribo-test Incorporation of Fe in debris itself The formation of the graphitic layer sensitive to humidity Gradual change of friction coefficient Abrupt change of friction coefficient

22. Friction Coefficient with Humidity Change during Tribo-test The effect of Fe in debris on the friction behavior The formation of the graphitic transfer layer highly sensitive to humidity ` The immediate drop of the friction coefficient RH : 90 %RH : 0 %

23. Conclusions Using steel balls, the tribological behavior of DLC film was highly affected by humidity. Incorporated Fe in debris by wear of the steel ball enhanced the formation of highly graphitic layer. The graphitic transfer layer was strongly sensitive to the humidity. When a graphitic transfer layer was formed, the friction coefficient of DLC film increased in humid environment. Counterface materials should be chosen carefully in order to control the tribological behavior of DLC films.