Mechanism of the improvement of the shape memory effect by "training" and ausforming in Fe-Mn-Si based shape memory alloys

The effects of "training" and ausforming on the morphology of stress-induced martensite and its reversion behavior to austenite in Fe-14Mn-6Si-9Cr-SNi and Fe28Mn-6Si-5Cr(mass%) alloys have been studied using atomic force microscopy (AFM), with the aim of clarifying the mechanism of the improvement of the shape memory effect. It is found that uniformly distributed thin martensite plates with a single variant nature are formed in a grain for both of the trained and ausformed samples. Those martensite plates can almost completely revert to the parent phase by shearing process, which is opposite to that of the forward transformation. This complete reverse transformation produces a perfect shape memory effect.