Mn Si Shape Memory Alloys Research Articles

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

AbstractThe 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.

Physical properties controlling shape memory effect in FeMnSi alloys

The variation of magnetic susceptibility with martensitic and magnetic phase changes is examined in FeMnSi shape memory alloys using a Faraday type magnetic balance. The c a ratio of stress induced ε martensites is determined for each ε plate under a high voltage electron microscope. It is found that the magnetic properties and the c a ratios deduced from these measurements are well correlated with the complete and incomplete shape memory effect obtained in these alloys through the analyses of thermally activated dislocation motion. The optimum conditions to obtain a complete shape memory effect are discussed on the basis of these findings, which were obtained over a wide temperature range (4.2–400 K).