Influence of substrate bias on structural and tribo-mechanical properties of pulsed magnetron sputtered TiN-WSx hard-lubricious coating

Lubricious WSx was codeposited with hard TiN to improve tribological property of the latter. Effects of substrate bias on structural and tribo-mechanical properties of composite coatings were investigated. Tribologically favourable (002) orientation of WS2 diminished with increase in bias. Surface morphology became increasingly compact up to −70 V. Adhesion, hardness and tribological characteristics were strongly influenced by applied bias. At 0 V, low hardness and adhesion led to localized detachment and consequent lump formation of coating in pin-on-disc test. At −90 V, pulverisation of hard, brittle coating material was observed. Superior tribological performance at intermediate bias of −40 V has been discussed in light of balanced combination of WSx content, adhesion and hardness of the composite coating.