Effect of Aging Heat Treatment on Precipitates and Mechanical Properties of Ti-Cr-Sn Superelastic Alloys with High Sn Content

抄録

In metastable β titanium alloys, superelasticity induced by martensitic transformation can be achieved by lowering the phase stability of the β phase. However, reducing the stability of the β phase also promotes the formation of the isothermal ω phase, which suppresses martensitic transformation and leads to embrittlement. The addition of Sn and Al effectively inhibits the formation of the isothermal ω phase; however, these elements also promote the formation of the isothermal α′′ phase in β-type titanium alloys. In this study, we conducted aging heat treatment on two Ti-Cr-Sn alloys exhibiting superelasticity at room temperature and investigated the resulting aging products and mechanical properties. In alloys with low Sn concentrations, aging at low temperatures led to the formation of the isothermal ω phase, whereas in alloys with high Sn concentrations, the isothermal α′′ phase formed instead of the isothermal ω phase. Both alloys in which the isothermal ω phase formed and those in which the isothermal α′′ phase formed exhibited a loss of superelasticity and significant embrittlement.