Anomalous stress-strain behavior of NiTi shape memory alloy close to the border of superelastic window

In this work, we report an anomalous phenomenon on superelastic cycling of NiTi shape memory alloys when deforming at the temperature close to border window. New unexpected effects are found—(i) critical stress for inducing martensite transformation during second loading cycle is higher than that first cycle; (ii) plateau decreases original level strain overcomes limit (iii) transition from good superelasticity in fully irreversible second. We propose defects generated window impede following stress-induced martensitic transformations, leading increase beyond yield B2 matrix, and thus functional fatigue alloys.