Low Temperature Nano-Tribological Study on a Functionally Graded Tribological Coating Using Nanoscratch Tests

Previous studies on low temperature tribological investigations were limited to macro-scale studies because of the lack of suitable instrumentation. This limitation has been overcome using a newly developed low temperature nanoscratch tester capable of characterizing the scratch resistance of coatings down to −30 °C. The scratch resistance and mechanical properties of a functionally graded a-C:H(Ti)/TiCN/TiN/Ti coating have been investigated for temperatures ranging from 25 to −30 °C. It has been found that the a-C:H(Ti)/TiCN/TiN/Ti coating failed at high loads by cracking and spallation during the room-temperature scratch tests. Fractography suggests that these failures originate from or close to the interface between the top a-C:H(Ti) and the TiCN layers. Decreasing the test temperature from 25 to 0 °C resulted in increased values in H, H/E _r and H ³ /E _r², consistent with improved crack- and wear resistances, with further smaller improvements being achieved on further decreasing the temperature to −30 °C.