Surface hardening of NiTi shape memory alloy induced by surface nanocrystallization via surface mechanical attrition treatment

In terms of grain refinement mechanism induced by plastic deformation, NiTi shape memory alloy (SMA) was processed by means of surface mechanical attrition treatment (SMAT) in order to achieve surface nanocrystallization for surface hardening. The cross sectional microhardness of the SMAT treated NiTi SMAs was measured, in comparison with those of the residual stress relaxation and recrystallization annealled NiTi specimen. The results show that surface nanocrystallization induced by grain refinement enhanced the surface hardness of NiTi SMAs.