Self-adaptive lubricating behavior of VAlN/Ag multi-layer coating at simulated operating conditions

Abstract

Solid lubricating coatings play a crucial role in preventing friction and wear failure of the hot-end sliding components in aviation engines. In this study, VAlN/Ag multi-layer coatings with excellent interfacial matching were fabricated using a hybrid magnetron sputtering technique. The type and energy of discharge plasmas were analyzed to comprehend their effects on depositing coatings. The coatings exhibit self-adaptive lubrication properties during the designed consecutive friction with stepwise heating from 25 °C to 650 °C. The microstructure evolution during early friction facilitates sufficient tribo-chemical reaction at 650 °C, leading to the formation of a distinctive "ball-on-rail" structure that significantly reduces friction coefficient. Based on the first-principles calculations, it was found that the bond energy of Ag−O is lower than that of V−O in both AgVO₃ and Ag₃VO₄, which promotes slipping along the (110) crystal plane and contributes to exceptional tribological properties. The fatigue wear failure mechanism of hard coatings under the thermal-force coupling effects has been elucidated, alongside an exploration of consecutive tribology mechanism at atomic scales over a wide temperature range.