Back stress and shape recoverability during reverse transformation in an Fe-based shape memory alloy

In an Fe–9%Cr–5%Ni–14%Mn–6%Si polycrystalline shape memory alloy (SMA), the macroscopic shape recoverability is measured, after the stress-induced martensitic transformation, during heating under several values of hold stress. The increase in the maximum stress during mechanical loading and in the hold stress during thermal loading reduces the shape recoverability, reconfirming that the shape recoverability decreases with the smaller back stress. A phenomenological model is proposed by assuming that the local back stress is proportional to the volume fraction of martensite and that the martensite variants transform back to the parent phase shape-reversibly or shape-irreversibly depending on the value of the back stress. The model works well to describe the experimental observations and explains successfully, the effect of the back stress on the shape recoverability.