Wear-resistant CrCoNi nanocrystalline film via friction-driven surface segregation

Revealing the frictional behavior through the lens of structural and chemical evolution is crucial for comprehending the exceptional wear-resistance of alloys with complex composition. Here, we propose that superior wear resistance can be achieved via dynamic surface segregation during sliding at room temperature. This strategy was demonstrated in CrCoNi multi-principal element alloy (MPEA) films with nano-grain structure, which exhibit a remarkably low wear rate that is <50 % of that for their VCoNi counterpart. Such distinct wear behavior is attributed to the specific friction-driven Ni segregation on the CrCoNi surface, which facilitates the preferential oxidation and formation of a nanocomposite protective layer with equiaxed nanograins uniformly embedded in an amorphous matrix. This wear-induced unique microstructure accommodates sliding-induced plastic deformation against damage and is responsible for the superior wear-resistance. Having revealed these fundamental mechanisms by experiment and simulation, this study provides a brand-new perception for designing self-adaptive MPEA surfaces. This involves adjusting the evolution of deformation layers with specific structure and chemistry, precisely engineered for tribological applications.