The effect of stress on soft modes for the phase transformation in a Ti-Ni alloy

Abstract
The softening of phonon modes is sensitive to stress. Both the internal tensile stress formed by Ti11Ni14 precipitates in Ni-rich Ti-Ni alloy and the internal stress introduced by thermal cycling in equiatomic Ti-Ni alloy have strong effects on the softening of phonon modes, especially on phonons with polarization vectors which are closely related to the R-phase transformation. The increase in the amount of R phase is the main effect of ageing and thermal cycling Ti-Ni alloy; this results in remarkable improvement in the shape memory effect and the pseudo-elasticity of the material. The negative effect of a compressive stress on the R-phase transformation has been experimentally confirmed.

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