Wear behaviour of martensitic NiTi shape memory alloy under ball-on-disk sliding tests

• Revealed three stages of surface degradation process of martensitic NiTi SMA.
• Proposed a model to describe the deformation distribution in the contact area.
• Estimated the contact stresses and discussed/explained the observed wear process.
• Observed a crown-like structure for the first time and explained its origin.
• The results are useful for limiting the wear process of NiTi SMAs in applications.

Ball-on-disk sliding wear tests were conducted on martensitic NiTi shape memory alloy against an alumina counter ball. The wear features and coefficients of friction of the samples subjected to different loads and sliding cycles were investigated to reveal the degradation process of the NiTi surface. Three stages of degradation were identified, namely, a near-zero wear stage, a transition wear stage and an abrasive wear stage. A special wear feature, herein referred to as the “crown-like structure”, was produced under near-zero and transition wear conditions and was observed for the first time in this study. The mechanisms of the surface degradation process are further discussed with respect to the deformation distribution in the vicinity of the contact area under different loads.