Shape memory characteristics of NiTi alloy wire under various constrained stresses

摘要

The present research aims to understand the transformation temperatures and recovery strain of NiTi wires during heating and cooling under various constrained stresses. Both constrained stress and annealing temperature have significant effects on the shape memory characteristics. In general, increasing constrained stress causes an increase of the austenitic (A_s~σ and A_f~σ) and martensitic (M_f~σand M_f~σ) transformation temperatures and a decrease of the recovery strain. This effect can be attributed to that the constrained stress inhibits the austenitic transformation, and thus more volume fraction of the martensite is retained during heating. The high annealing temperature leads to the decrease in the recovery strain.