The Effect of Stress on the Lattice Instability of a TiNi Alloy

Abstract

AbstractThe behavior of the phase transformation in equiatomic TiNi alloy during thermal cycling under applied stresses is studied by measuring the electical resistivity and investigating the diffuse streak diffraction of electron and the X‐ray diffraction. The results show that the stress has a strong effect on the lattice instability. The tensile stress promotes the softening of phonon modes which relate to the nucleations of the R phase and the martensitic phase so that the tensile stress is favourable for the formation of the R phase and martensitic phase, while the compression stress has negative effects. The investigation shows that the effect of stress on 〈111〉 longitudinal phonon mode is larger than that on 〈110〉 transversal phonon mode. The tensile stress enhances particularly the softening of 〈111〉 longitudinal phonon mode which corresponds mostly to the R phase transformation, but the compression stress is unfavourable for it. It is identified that the diffuse streak diffraction patterns of electron associated with more R phase induced by the tensile stress arises from the softening of 〈111〉 longitudinal phonon mode.