Phase strains and crystalline structures of multi-phases Nb-Ti-Ni alloys under tensile plastic deformation were investigated by X-ray diffraction technique. Cold-rolled Nb-Ti-Ni hydrogen permeation alloy which consists of the primary phase, (Nb,Ti), and the eutectic phases, (Nb,Ti) + TiNi, was used as a specimen A diffracted X-ray profile from the specimen during tensile loading was measured by using synchrotron white X-ray. As a result, it was found that an integrated intensity of diffracted X-ray from B2-ciystalline structure of TiNi phase began decreasing when an applied plastic strain was more than 5%, and a diffracted X-ray peak of B19'- crystalline structure of it appeared at applied plastic strain of about 10%. Therefore, it was confirmed that a phase change in crystalline structure of TiNi phase in the specimen occurred under the large plastic deformation. And, crystals of(Nb,Ti) phase were yielded earlier than those of TiNi phase, and they strongly showed an anisotropy of crystal plasticity.
