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Environmental Dependence of Tribological Behavior of DLC Films

Environmental Dependence of Tribological Behavior of DLC Films. Se-Jun Park and Kwang-Ryeol Lee Future Technology Research Division Korea Institute of Science and Technology. AEPSE 2003, Jeju, 2003. 10. 1. Properties of Solid Carbon. Wear Rate. Friction Coefficient. DLC. WC. TiN. CrN.

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Environmental Dependence of Tribological Behavior of DLC Films

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  1. Environmental Dependence of Tribological Behavior of DLC Films Se-Jun Park and Kwang-Ryeol Lee Future Technology Research Division Korea Institute of Science and Technology AEPSE 2003, Jeju, 2003. 10. 1.

  2. Properties of Solid Carbon

  3. Wear Rate Friction Coefficient DLC WC TiN CrN TiCN 2.0 1.6 1.2 0.8 0.4 0.2 0.4 0.6 0.8 1.0 Relative value Tribological Properties of Hard Coatings

  4. Applications of DLC Film

  5. Problems of DLC Films • Thermal Instability • Degradation at High Temperature (400 – 600oC) • High Residual Compressive Stress • Max. 10 GPa • Poor Adhesion • Stable Chemical Bonds • Especially on Ferrous Materials • Environmental Dependence of the Tribological Properties

  6. Humidity Dependence of the Tribological Behavior R. Gilmore et al Surf. Coat. Technol. 133-134, (2000), 437

  7. DLC Tribochemical Reaction • The environmental dependence strongly implies that the tribochemical reaction between the test environment, the film and the counterface materials are significant.

  8. Purposes of The Present Work • To investigate systematically the friction behavior of DLC film in various test environments including relative humidities. • To find the reason for the humidity dependence of the tribological behavior of DLC film in the point of tribochemical reaction. • What happens in Si incorporated DLC films?

  9. Film 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.%

  10. Friction Test • Ball : AISI 52100 steel ball • Normal Load : 4 N • Sliding Speed : 20 cm/s • Temperature : Room temperature • Environmental Gas : • Ambient atmosphere • (relative humidity : 0 – 90 %) • High pure oxygen

  11. Humidity Dependence of Friction Si-DLC Pure DLC

  12. RH 0 % RH 50 % RH 90 % 250 ㎛ 100 ㎛ 100 ㎛ 100 ㎛ Scar Surface with Humidity Variation

  13. Raman Spectra of the Transfer Layer

  14. Chemical Composition of Debris

  15. Track Ball Wear Rate of Track and Ball

  16. (a) (b) (e) 250㎛ 2 ㎛ 2 ㎛ 2 ㎛ (c) (d) 250㎛ 250㎛ (f) (e) RH=0% RH=50% RH=90%

  17. Fe Fe-O a-C:H Fe Fe-O a-C:H Fe Fe-O a-C:H

  18. Debris Composition & Friction M. G. Kim et al., Surf. Coat. Tech. 112, 204 (1999).

  19. In Dry Oxygen Environment

  20. (a) 2 ㎛ 2 ㎛ (b)

  21. Fe Fe-O a-C:H a-C:H Al2O3 a-C:H in Dry Oxygen Environment

  22. The Environmental Dependence • The increased friction coefficient in humid environment is closely related with the increased Fe concentration in the debris due to the enhanced surface oxidation of the steel ball. • The humidity dependence is not an inherent property of the DLC films. • The Fe rich debris itself degrades the lubricating property of the DLC film. • The Fe rich debris enhance the agglomeration of small debris into larger one that requires larger energy dissipation to be deformed during sliding

  23. Wear Rate of the Ball Si-DLC DLC Chemical Composition of Debris with Humidity Change

  24. 90 % 0 % 50 % Si-DLC 3 ㎛ 3 ㎛ 3 ㎛ 3 ㎛ 3 ㎛ 3 ㎛ DLC

  25. Raman Spectra of the Transfer Layer Si-DLC DLC

  26. RH 0 % RH 50 % RH 90 % 250 ㎛ 250 ㎛ 250 ㎛ Scar Surface with Humidity Variation 100 ㎛ 100 ㎛

  27. Friction in Dry Oxygen Environment

  28. Si-DLC 3 ㎛ DLC 3 ㎛

  29. Wear Rate of Ball and Track in O2 Env.

  30. Raman Spectra of the Transfer Layer

  31. The Environmental Dependence • Fe rich debris formed by oxidation of the steel ball increased the friction coefficient in humid environment. • Less dependent on the test environment • Bond structure of the debris varied with relative humidity. Diamond-like structure in humid environment suppress the agglomeration of the debris.

  32. Conclusions • Humidity dependence of the friction behavior of DLC film is not an inherent property of the DLC film. • Humidity dependence should be understood in terms of the tribochemical reaction of the tribo-system. • Two major factors were suggested. • Fe concentration in the debris : Conterface Materials • Debris agglomeration : Chemical bond of the debris

  33. Acknowledgement • Discussion with Dr. H-S. Kong, Dr. E-S. Yoon & Dr. J-K. Kim. • Financial Support • Center for Nanostructured Materials Technology • Center of Advanced Plasma Surface Engineering • J&L Tech. Co., Ltd.

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