A Novel Training-Free Cast Fe-Mn-Si-Cr-Ni Shape Memory Alloy Based on Formation of Martensite in a Domain-Specific Manner

The proposed key to producing a good shape memory effect in Fe-Mn-Si alloys is to reduce or even prevent the collisions between martensite bands. A method for realizing this is to make stress-induced martensite bands form in a domain-specific manner. We developed a novel training-free cast Fe-18Mn-5.5Si-9.5Cr-4Ni alloy with residual lathy delta ferrite based on this idea. The recovery strain reached 6.4% only after annealing the cast Fe-18Mn-5.5Si-9.5Cr-4Ni alloy. Microstructure observations indicated that the lathy delta ferrite made the stress-induced martensite form in a domain-specific manner by first subdividing grains into smaller domains. We hypothesize that through adjusting alloy compositions, solidification parameters, and heat treatment technique, the shape recovery of cast Fe-Mn-Si alloys can be further improved. Such a finding will provide a novel method for developing training-free Fe-Mn-Si shape memory alloys.