Probing for mechanical and tribological anomalies in the TiC/amorphous hydrocarbon nanocomposite coating system

Abstract

We have performed a detailed examination of the mechanical properties and the friction and wear characteristics of titanium-containing amorphous hydrocarbon (Ti–C:H) coatings as a function of the Ti composition from 0 to 45 at.%. Elastic modulus and hardness were measured with instrumented nanoindentation. Friction coefficient and coating wear rate during unlubricated sliding against WC–Co in a ball-on-disk configuration were also measured. Deposited by inductively coupled plasma (ICP)-assisted hybrid chemical vapor deposition/physical vapor deposition (CVD/PVD), these Ti–C:H coatings consist of nanocrystalline TiC clusters embedded in an a-C:H matrix, and are thin film TiC/amorphous hydrocarbon (a-C:H) nanocomposite materials. As the Ti composition increases, the elastic modulus and hardness of the coatings exhibit smooth variations. In contrast, relatively abrupt transitions occur in the friction coefficient and the wear rate of the coatings over a relatively narrow (20–30 at.%) Ti composition range. Our results indicate bimodal friction and wear behaviors for the TiC/a-C:H nanocomposites, a-C:H-like at Ti compositions below 20%, and TiC-like at Ti compositions above 30%. Our results indicate that two different coating wear mechanisms operate as the volume fraction of nanocrystalline TiC clusters changes. Over the entire range of Ti compositions examined, no anomalous changes in elastic modulus or hardness of the Ti–C:H coatings were observed.