Improving the Mechanical and Tribological Properties of NiTi Alloys by Combining Cryo-Rolling and Post-Annealing

By combining cryo-rolling and post-annealing treatments, the nanostructured NiTi alloy is produced. A differential scanning calorimetry measurement was used to test the effect of the preparation process on phase transformation. The cryo-rolling changes the tensile fracture of NiTi alloy to a ductile manner. Interestingly, the recovered structure exhibits significant strength improvement, while the tensile plasticity is still comparable to that of the coarse-grained structure. This optimized mechanical performance is due to the strengthening effect of refined microstructure and the high work hardening capability rendered by moderate dislocation density. Ball-on-plate reciprocating dry-sliding wear test reveals that the nanostructured NiTi alloy also has enhanced wear resistance, which is primarily ascribed to the high content of residue martensite formed during cryo-rolling. These results provide an effective route to optimize the mechanical and wear properties of NiTi alloys.