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.