Gaining flexibility in the design of microstructure, texture and shape memory properties of an Fe-Mn-Si-Cr-Ni alloy processed by ECAE and annealing

Abstract

The effect of ECAE on the properties of an Fe-15Mn-5Si-9Cr-5Ni shape memory alloy (SMA) was investigated. Phases, texture, microstructure, critical temperatures, mechanical and SM properties after severe deformation, and the effect of annealing were analysed. One ECAE pass develops a shear texture. There is a large 〈101〉 component in the extrusion direction, which is near the ideal 〈414〉 for martensitic transformation activation. The pressing did not refine the previous as cast structure but introduced dislocations and ε-martensite. Thus, the stress to induce the γ→ε martensitic transformation, σγ→ε, reached 620MPa, and the quantity of ε-martensite formed after compression was limited. The degree of shape recovery was reduced, while the reverse transformation temperatures increased. Heat treatments above 800°C activated recrystallization. As annealing temperature increased, new grains nucleated and grew, reaching a size of 53μm after heating to 1000°C. For this condition, σγ→ε was 430MPa, and the best shape recovery was achieved, 64%.