Martensitic Transformations in Ti-Ni alloy Single Crystals

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We carried out joint research with Russia and Japan systematically on the martensitic transformations in Ti-Ni-based single crystals, and obtained the following results. (1) Three distinct types of martensitic transformations occur in Ti-Ni alloy systems depending upon composition. By measuring elastic constants of Ti-Ni, Ti-Ni-Cu and Ti-Ni-Fe systematically by parallelepiped resonance method, we obtained the following interesting results. Both elastic constants c' and cィイD244ィエD2 soften with decreasing temperature. The temperature dependence of elastic anisotropy A = cィイD244ィエD2/c' differs greatly, depending upon the types of transformations. Thus, it was found that there is a close relationship between the types of transformation and elastic anisotropy. Furthermore, the origin for the appearance of monoclinic martensite B19' was explained by the temperature dependence of cィイD244ィエD2 and A. (2) By neutron inelastic scattering measurement, phonon softening was found near the Brilloiun zone boundary of 1/2<110><11ィイD4-ィエD40> branch for B2-B19 (orthrombic) transformation in Ti-30Ni-20Cu alloy. (3) By in-situ electron microscopy observations of Ti-Ni-Fe alloy, the pre-martensitic behavior of B2-R phase transformation was clarified. (4) The structure of R-phase was determined accurately. (5) The orientation dependence of superelasticity in Ti-Ni alloy was clarified by tension and compression test.