Ausforming treatment (deformation of austenite at temperature above Md) can improve the shape memory effect of Fe-MnSi based shape memory alloys, however, the mechanism of this improvement is not so clear. In this paper, the influence of ausforming treatment on stress-induced martensitic transformation and its reverse transformation in an Fe-28Mn-65i-5Cr (mass%) shape memory alloy has been studied using atomic force microscope (AFM) and TEM aiming to clarify the origin of this improvement. It was found that the ausforming treatment at 970K by 9% pre-straining, which is the optimum condition for improving shape memory recovery, can introduce many uniformly distributed stacking faults on the same slip plane in austenite. When an external stress is applied to such an ausformed specimen for shape change, uniformly distributed martensite bands with the same variant are produced in a grain due to the assistance of those preexisted stacking faults. When being heated over AS, these martensite bands are nearly completely reverse-transformed to parent phase through the same atomic pass as for the forward transformation, so a nearly perfect shape memory effect (over 90%) is obtained.
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