Enhancing tribological performance of NiAl-Bi2O3-Cr2O3 composite coating via in-situ grown NiBi compound

To provide a feasible solution for realizing low friction and wear on the surface of moving parts in a wide temperature range, we report a facile strategy to achieve the improved tribological capability of a NiAl-Bi2O3-Cr2O3 composite coating by applying heat treatment. The heat treatment delivers structural densification and compositional homogeneity of the coating while promoting the in-situ generation of a diffusely distributed intermetallic compound of nickel bismuth (NiBi). When performing rotational dry sliding tests against Al2O3 counterpart ball in air, the tribo-induced decomposition of the NiBi compound and the spontaneous interaction between NiBi and its oxidative environment lead to the formation of an amorphous yet deformable oxide surface, which is responsible for exceptional tribological properties in a wide temperature range. Particularly, the tribological performance is improved significantly from room temperature (RT) to 400 °C for the annealed samples compared to the non-annealed ones: The friction coefficient decreases by 23.6% at RT and 27.9% at 400 °C, and the wear rate decreases by 51.4% at RT and 81.2% at 400 °C. With these findings, we establish a general approach to the improvement of friction-reduction and anti-wear properties in cermet coatings.