Reasons for incomplete shape recovery in polycrystalline Fe–Mn–Si shape memory alloys

Quantitative surface relief analysis proved that the incomplete shape recovery of a polycrystalline Fe–28Mn–6Si–5Cr alloy was not caused by slip deformation on loading but by irreversible phase transformation on heating, under given conditions ([54¯1¯] tensile axis, 5.9% strain). The observed area showed a higher recovery strain than the macroscopic recovery strain, implying inherently high reversibility. However, the value was significantly lower than that of a single crystal, due to the geometric constraint from surrounding grains, which reflected different transformation dislocations between forward and reverse transformations.