An improvement of shape memory effect in Fe-Mn-Si shape memory alloy by training process under impact tensile loading

The effect of impact-load training on shape recovery has been investigated in an Fe-based shape-memory alloy. The Fe-28Mn-6Si-5Cr alloy samples underwent repeated training involving 7 % tensile straining followed by subsequent heat treatment. The results indicated that shape recovery after heating improved with an increasing number of training cycles under both quasi-static and impact loading conditions. However, beyond seven training cycles, only marginal improvements were observed for both loading conditions. The ratio of shape recovery under impact loading condition was higher than that under quasi-static condition after the fifth training cycle. The recovery strain achieved after six cycles of impact-loading training was 93 %. Volume resistivity measurements revealed that the threshold stress required for forward martensitic transformation decreased with an increasing number of training cycles. In addition, the effect of impact-loading training was examined using electron backscatter diffraction (EBSD) measurements. From the EBSD analyses after loading, the martensite generated under the impact loading condition was predominantly a single variant in a grain, whereas multiple variants were frequently detected after quasi-static loading.