Environmental Dependence on Tribological Behavior of Diamond-like Carbon Films with Nano-undulated Surface Jin Woo Yi a,b, Se Jun Park a, Kwang-Ryeol Lee a, Seock-Sam Kim b a Korea Institute of Science and Technology, Seoul, Korea b Kyuongpook National University, Daegu, Korea THE INTERNATIONAL CONFERENCE ON METALLURGICAL COATINGS AND THIN FILMS ICMCTF 2006 May 1-5, Town and Country Hotel, San Diego, California, USA

2 Merit of Diamond-like Carbon Wear Rate Friction Coefficient

3 Demerit of Diamond-like Carbon The frictional behaviors of DLC film largely depends on environmental conditions such as relative humidity.The frictional behaviors of DLC film largely depends on environmental conditions such as relative humidity. A.Gilmore et al., Surf. Coat. Technol., (2000) 437

4 Humidity Dependence of Frictional Behavior of DLC film S.J.Park et al., Diamond Relat. Mater. 12 (2003) 1517 Relative humidity Friction coefficient Formation of Fe-rich debrisFormation of Fe-rich debris (Degradation of lubricant properties of DLC film) (Degradation of lubricant properties of DLC film) Increase of the debris sizeIncrease of the debris size

5 Possibility of Nano-undulated Surfaced DLC film DLC film with nano-undulated surface could suppress the dependence of environmental conditions.DLC film with nano-undulated surface could suppress the dependence of environmental conditions. S.J. Park et al., Diamond Relat. Mater., 14 (2005)

6 Purpose of This Work Tribological behavior of nano-undulated DLC film surface with various surface roughness in different humid environments.Tribological behavior of nano-undulated DLC film surface with various surface roughness in different humid environments. Investigating the relationship between the surface roughness and the humidity dependence on frictional behavior of DLC filmsInvestigating the relationship between the surface roughness and the humidity dependence on frictional behavior of DLC films

7 Fabrication of DLC Film with Nano-undulated Surface Annealing Ni-thin Film DC magnetron sputter Deposition Pressure : 1.33 Pa Current : 200 mA Voltage : -430 V Film Thickness : 3 ~ 9 nm DLC film with undulated surface RF PACVD (13.56MHz) Precursor Gas : CH 4 Deposition Pressure : 1.33 Pa Bias Voltage : -150 V b Film Thickness : 100±10 nm DLC Deposition

8 Surface Roughness of DLC Films RRMS=9.4 nm RMS=8.1 nm RMS=0.1 nm RRMS=11.8 nm

9 Raman Spectra

10 Environmental Tribo-meter Wear-test conditionWear-test condition – – Counter-ball : Steel bearing ball (Dia. 6 mm) (AISI 52100) – – Normal load : 200 gf (2 N) – – Sliding speed : 11.5 cm/sec – – Relative Humidity : 0 ~ 90 % – room temperature – – Running Time : 10,000 cycles Weight Load Cell Counter- ball Holder Film Rotation Humid Controller Rotary Pump

11 Frictional Behavior

12 Mean Friction Coefficient

13 Auger Spectra of Wear Debris

14 Raman Spectra of Transfer Layer

15 Morphology of Transfer Layer 200μm RH 0%RH 50%RH 90% RH 0%RH 50% RH 90% RMS 0.1 nm RMS 11.8 nm 200μm Fe-oxide debris Diamond-like Diamond-like No Fe-oxide No Fe-oxide Wear Scar

16 In Relative Humidity 90 % Transfer Layer Fe-oxide Particle Fe-oxide Transfer Layer Fe-oxide Particle Fe-oxide In case of DLC film with smooth surface In case of DLC film with rough surface Discussion

17 Conclusions Controlling the surface roughness of DLC film in nano-scale can suppress the environmental dependence on frictional behavior of DLC film. Controlling the surface roughness of DLC film in nano-scale can suppress the environmental dependence on frictional behavior of DLC film. - In case of DLC film with smooth surface, the bond structure of transfer layer reveals graphitic materials and a lot of Fe-oxide is observed in the transfer layer with increase of relative humidity. - In case of DLC film with rough surface, the bond structure of transfer layer reveals diamond-like materials and less Fe-oxide is observed in the transfer layer.

18 T hanks for Y our A ttention !!!

19 Morphology of Wear Debris RH 0% RH 50% RH 90%