Temperature-insensitive ultralow lubrication of sputtered WSN coatings: Insights into constant, ramping, and cycling temperatures from room to 400 °C

This study introduces a breakthrough in self-lubricating WS₂–nitrogen (WSN) coatings engineered for demanding applications across industries requiring adaptive durability and high performance. Deposited via nonequilibrium reactive magnetron sputtering in N₂-containing atmospheres, the WSN coatings demonstrate exceptional tribological behavior across a range of extreme conditions, including constantly discrete high temperatures, ramping temperatures either during heating or cooling and wide temperature cycling from room temperature to 400 °C. The WSN coatings exhibit an extremely low coefficient of friction (CoF = 0.02) up to 400 °C, with high thermal stability and superior triboperformance. Moreover, the coatings possess favorable tribo-reversibility under 400 °C ↔ room temperature cycles. Transmission electron microscopy analysis verified the self-lubricating, tribologically reversible, and ultralow lubrication mechanisms of the WSN coatings. However, under high-temperature tribosliding, the WS₂ layer still dynamically forms a self-organized, layered interface structure that continuously adapts to sliding conditions, ultimately enabling sustained superlubricity and tribological reversibility. Oxidation during high-temperature tribosliding actually has only a minor degrading effect on friction provided that the coatings retain sufficient sulfur to predominantly form WS₂ lubricant agents. This study provides novel insights into the development of advanced tribocatings exhibiting adaptive ultralubrication under various temperature conditions.