Abstract: Superelastic NiTi shape memory alloys are widely used in functional components that undergo cyclic deformation and inevitably experience frictional wear at contact surfaces. In this study, nanocrystalline NiTi alloys with grain sizes ranging from 20 to 90 nm were fabricated to investigate their sliding wear behavior. The friction coefficient remained relatively stable across all grain sizes, whereas the wear rate decreased significantly with grain refinement. Specifically, reducing the grain size from 90 to 20 nm lowered the wear rate by ∼25%. Microstructural analysis revealed that a thin amorphous/crystalline nanocomposite layer formed in the subsurface of the 90 nm alloy, while a much thicker fully amorphous layer developed in the 20 nm alloy. The enhanced hardness and strength of this amorphous subsurface layer were responsible for the improved wear resistance. These findings highlight the potential of nanoscale grain refinement and amorphization as an effective microstructural design strategy for developing wear-resistant NiTi shape memory alloys.

Key words: Wear and friction, NiTi alloy, Grain size effect, Amorphization, Plastic deformation