In situ tribology of nanocomposite Ti–Si–C–H coatings prepared by PE-CVD

Abstract In situ tribometry was used to examine the role of third bodies for the friction and wear behaviour of five hard Ti–Si–C–H coatings produced by plasma-enhanced chemical vapour deposition. Coatings exhibited nanocomposite structures consisting of nanocrystalline titanium carbide surrounded by amorphous carbon containing H and Si (the latter being present in all coatings but one). From nanoindentation testing, the hardness for the coatings was between 22 and 35 GPa. An inverse correlation was found between hydrogen content, which was determined by Raman spectroscopy, and hardness. A custom-built in situ tribometer, equipped with a hemispherical sapphire slider, was used for reciprocating pin-on-flat wear tests. The buried interface was examined in situ with video microscopy, allowing for observation of third body formation (transfer films, wear debris) and velocity accommodation modes. The formation of a stable transfer film, which was dependent on coating chemistry and humidity level, resulted in increased wear resistance compared to coatings that did not form a transfer film, regardless of the coatings’ mechanical properties. Results from this study suggest an approach to optimising the tribological performance for hard protective coatings that does not rely solely on mechanical properties but is complemented by investigations on the third body behaviour.