Effect of cyclic deformation on thermo-mechanical characteristics in Ti-Ni-Cu alloy wires with various copper contents

The effects of cyclic deformation and copper content on the thermo-mechanical characteristics in Ti-Ni-Cu alloys were investigated. Thermo-mechanical cyclic tests were conducted for various strains at a fixed heating temperature. Specimens were Ti-45Ni-5Cu, Ti-40Ni-10Cu and Ti-37Ni-13Cu (at%), annealed at 673 K for 3.6 ks after cold drawing with 30% reduction. The results show that the change of functions such as residual strain and the strain energy is significant in early cycles, but it becomes insignificant after 100 cycles. Also, the change of functions with number of cycles shows the dependence on copper content. In order to clarify the effects of cyclic deformation and copper content on the degradation of functions, the volume fraction of slip-deformed martensite is evaluated by a two-phase model consisting of the parent phase and the martensitic phase connected in series. The volume fraction of slip-deformed martensite represents the variation of the residual strain and the degraded recovery strain energy with number of cycles and copper content. Based on these results, it is concluded that the volume fraction of slip-deformed martensite is a measure which represents the effects of cyclic deformation and copper content on the degradation of functions.