Friction and wear behavior of atmospheric plasma sprayed Ni-50at.% Bi coating at room temperature to 400 °C

To meet the growing demand for high-temperature lubricating coatings in aerospace and energy systems, this study proposes a plasma-sprayed Ni-50at.% Bi coating designed to achieve adaptive friction reduction from room temperature (RT) to 400 °C. By synergizing the low-temperature lubricity of Bi with the temperature-dependent tribochemical interactions between Ni, Bi, and oxygen, the coating demonstrates exceptional wear resistance across a wide temperature range. Below 200 °C, the soft Bi phase mitigates abrasive wear through shear-induced lubrication. At 300 °C, in-situ formed NiBi intermetallic compounds with ordered grain boundary structures dominate the tribolayer, reducing friction and wear via low-shear deformation. When temperatures reach 400 °C, synergistic effects of NiBi compounds and friction-generated oxides (Bi2O3, NiO, and Bi7.47Ni0.53O11.73) can mitigate abrasive and adhesive wear. This work provides a novel strategy for designing self-adaptive lubricating coatings, significantly broadening the operational temperature limits of traditional Ni-based coatings in extreme environments.