Peculiarities of residual strain accumulation during thermal cycling of TiNi alloy

► Fraction of forward martensite transition influences accumulation of residual strain. ► If less than 50% of forward transition takes place then, no residual strain is found. ► If 75% and more of forward transition occur then residual strain is observed. ► Accommodation of martensite variants occurs elastically in the 50% of MT. ► Plastic accommodation takes place only in the last quarter of temperature range of MT. Strain variation on thermal cycling of the TiNi alloy under a constant stress of 50 MPa through the temperature range of complete as well as incomplete forward martensitic transformation was studied. The thermal cycling of the alloy through the temperature range of incomplete forward martensitic transformation was carried out to realize 25%, 50% or 75% of temperature range of forward phase transition. The thermal cycling of the TiNi alloy through the temperature range of the complete forward martensitic transformation resulted in observation of “training effect” (an increase in values of transformation plasticity and shape memory effects strain) and accumulation in residual plastic strain. It was shown that observation of “training effect” as well as accumulation of residual strain depended on the completeness of the forward martensitic transformation. As higher the fraction of temperature range of forward martensitic transformations on thermal cycling as stronger variation in values of shape memory effects and higher the accumulated plastic strain on the thermal cycling of the TiNi alloy. These phenomena were due to that the martensite accommodation process was elastically in the early stage of forward martensitic transformation. The plastic accommodation of martensite took place on the final stage of forward phase transition.