Superelastic behavior of a β-type titanium alloy.

The superelasticity of a β Ti alloy, Ti-7.5Nb-4Mo-2Sn (in atom percent) was evaluated by using loading and unloading cyclic tensile tests under different thermomechanical conditions, and the effects of the plastic deformation, temperature, strain rate and cyclic loading on the superelasticity of the alloy were studied. It is found that, with the applied strain increasing, the stress inducing the reverse martensitic transformation σα″-β and the strain recovery rate η decreases. The increase of deformation temperature promotes σβ-α″, σα″-β and Δσ, and the temperature dependency of the stresses obeys the Clausius-Clapeyron relation. σβ-α″, σα″-β and Δσ are independent on the strain rate when it is lower than 8.35×10(-4)s(-1). However, when the strain rate is higher than 8.35×10(-4)s(-1), σβ-α″ and Δσ increase, but σα″-β decreased with increasing the strain rate. By cyclic loading and unloading to the maximum strain of 6% at 25°C under the strain rate of 1.67×10(-4)s(-1), the alloy exhibits a improved superelasticity after seventh cycles due to the training effect.