Effect of Ni on Stacking Fault Distributions in Fe-Mn-Si-Ni-Cr Shape Memory Alloys

Abstract

By varying the Ni content in the range between 4 and 10% in Fe-Mn-Si-Ni-Cr shape memory alloys, the effect of the Ni content on the distribution of stacking faults and e martensite plates in these alloys was studied in detail with optical and transmission electron microscopy. After the solution treatment followed by water quenching, e martensite was already present in the alloys containing less than 9% Ni. The volume fraction of e martensite decreased, however, remarkably with the increasing Ni content. In all alloys investigated, widely extended and densely overlapped stacking faults were observed. Also their densities decreased with the increasing Ni content. In addition to such large stacking faults, a large amount of short, imperfectly overlapped stacking faults was observed to be uniformly distributed in the 6% Ni alloy, in which the maximum shape memory effect was observed. It was suggested that such imperfectly overlapped short segments of stacking faults might be origins of stress-induced e martensite responsible for the shape memory effect