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Slip-rolling resistance of ta-C and a-C coatings up to 3,000 MPa of maximum Hertzian contact pressure

: Woydt, M.; Scholz, C.; Manier, C.A.; Brückner, A.; Weihnacht, V.


Materialwissenschaft und Werkstofftechnik 43 (2012), No.12, pp.1019-1028
ISSN: 0933-5137
Bundesministerium für Bildung und Forschung BMBF
03X2512; OTRISKO
Bundesministerium für Wirtschaft und Technologie BMWi
0327499B; PEGASUS
Deutsche Forschungsgemeinschaft DFG
WO 521/6-1
Deutsche Forschungsgemeinschaft DFG
WO 521/6-2
Journal Article
Fraunhofer IWS ()

The slip-rolling resistances of hard and stiff thin films under high Hertzian contact pressures can be improved by optimizing the "coating/substrate systems". It is known from former investigations that the so-called "egg-shell" effect is no general hindrance for high slip-rolling resistance of thin hard coatings. The coating stability depends more on specific deposition process and coating/substrate interface design. In this article it is experimentally shown, that pure amorphous carbon thin films with hardness between 15 and 63 GPa can be slip-rolling resistant several million load cycles under a maximum Hertzian contact pressures of up to 3.0 GPa. Whereas all coatings were stable up to 10 million load cycles in paraffin oil at room temperature, reduced coating lifetime was found in SAE 0W-30 engine oil at 120 degrees C. It was shown how the coating hardness and the initial coating surface roughness influence the running-in process and coating lifetime. No clear correlation between coating hardness and coating lifetime could be observed, but friction coefficients seem to be reduced with higher coating hardness. Very low friction down to similar to 0.03 in unmodified engine oils was found for the hardest ta-C film.