My Experience with Ti–Ni-Based and Ti-Based Shape Memory Alloys

The present author has been studying shape memory alloys including Cu–Al–Ni, Ti–Ni-based, and Ni-free Ti-based alloys since 1979. This paper reviews the present author’s research results for the latter two materials since 1981. The topics on the Ti–Ni-based alloys include the achievement of superelasticity in Ti–Ni alloys through understanding of the role of microstructures consisting of dislocations and precipitates, followed by the contribution to the development of application market of shape memory effect and superelasticity, characterization of the R-phase and monoclinic martensitic transformations, clarification of the basic characteristics of fatigue properties, development of sputter-deposited shape memory thin films and fabrication of prototypes of microactuators utilizing thin films, development of high temperature shape memory alloys, and so on. The topics of Ni-free Ti-based shape memory alloys include the characterization of the orthorhombic phase martensitic transformation and related shape memory effect and superelasticity, the effects of texture, omega phase and adding elements on the martensitic transformation and shape memory properties, clarification of the unique effects of oxygen addition to induce non-linear large elasticity, Invar effect and heating-induced martensitic transformation, and so on.