Low-Cycle Superelastic Response of a Titanium-Niobium ShapeMemory Alloy

摘要

Cyclic and time dependence of superelastic properties such as critical stress for stress-induced martensite (σ_(SIM)) irrecoverable strain levels, and stress hysteresis are crucial parameters to ensure stable operation in applications of shape memory alloys. In our studies on titanium-niobium shape memory alloys that have undergone various thermo-mechanical processes, declines in both σ_(SIM) and stress hysteresis with increasing cycle number were observed. More surprisingly, aging treatment at room temperature following cycling produced stress-strain behavior very similar to behavior of samples prior to cyclic deformation, and irrecoverable strain levels did not increase monotonically with increasing cycle number. Lowest irrecoverable strain levels and smallest evolution in the superelastic behavior were found in precipitated cold rolled or processed specimen by equal channel angular extrusion.