Effect of Cyclic Deformation on Thermo-Mechanical Characteristics in Ti-Ni-Cu Alloy Wires with Various Copper Contents

Abstract

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.

Effects of Pre-Strain and Heat Treatment Temperature on Phase Transformation Temperature and Shape Recovery Stress of Ti-Ni-Nb Shape Memory Alloys for Pipe Joint Applications

“…They then demonstrated that it could be used as an indicator of dislocation introduced by pre-strain. 12,13) In M transformation, the material stores elastic strain energy. This elastic strain energy reportedly assists in reverse transformation while resisting M transformation.…”

Constitutive Equation with Consideration of Slip-Deformed Martensite in the Deforming of Ti–Ni Shape Memory Alloy

“…(1 0 ) from start condition of the reverse transformation (t ¼ t s ) to finish condition (t ¼ t f ), the stressstrain relation during heating under stress-free condition can be expressed by the eq. (8). Relation between strain and volume fraction of martensite can also be represented by eq.…”

Effect of Pre-Strain on Transformation and Deformation Behavior in Ti–50 at%Ni Shape Memory Alloy

“…Then, the volume fraction of slip-deformed martensite with various pre-strains was defined as the eq. (1), 12,13) where, E A and E M are elastic moduli of parent phase and martensitic phase, respectively. Figure 2(a) shows a schematic diagram of stressstrain curve in the heating test under the constrained strain condition.…”

“…Authors have defined the remained fraction of martensitic phase in the parent phase as the volume fraction of slip-deformed martensite , and have clarified that the value of can be used as a criterion of pre-strain induced dislocation. 12,13) And also, elastic strain energy is stored in the materials by the martensitic deformation, and the energy promotes the reverse transformation, then it acts to restrain the martensite from transforming. [7][8][9][10] Therefore, if the elastic strain energy is released by the deformation of the martensitic phase, the transformation temperature increases.…”