Hot workability of FeMnSiCrNi shape memory alloy based on processing map and martensitic transformation

Abstract

Hot workability of Fe66Mn15Si5Cr9Ni5 (wt.%) shape memory alloy (SMA) with γ austenite and ε martensite at room temperature was investigated by establishing processing map and simultaneously considering martensitic transformation. All the FeMnSiCrNi samples subjected to hot deformation are composed of ε martensite and γ austenite. Furthermore, the higher temperature results in the larger fraction of ε martensite, whereas the higher strain rate leads to the smaller fraction of ε martensite. Simultaneously, the higher temperature or the lower strain rate leads to the larger grain size. In addition, dislocations, stacking faults and austenite twins appear in the deformed samples. According to processing map, the optimal hot processing parameters for the FeMnSiCrNi SMA is determined as the temperature range of 850–925 °C at the strain rate below 0.0008 s−1 and the temperature range of 925–1000 °C at the strain rate range of 0.001–0.03 s−1. Furthermore, the existence of ε martensite in the deformed FeMnSiCrNi samples has an adverse effect on shape memory effect of FeMnSiCrNi SMA. In addition, dynamic recrystallization (DRX) and subsequent martensitic transformation weaken the textures of the grains with γ austenite phase in the deformed FeMnSiCrNi SMA samples. Therefore, it is necessary to prevent FeMnSiCrNi SMA from being subjected to hot workability in the case of too high temperatures or too low strain rates.