Influence of annealing temperature on the shape memory effect of Fe–14Mn–5Si–9Cr–5Ni alloy after training treatment

The effect of annealing temperature on the shape memory effect (SME) of a Fe–14Mn–5Si–9Cr–5Ni alloy has been investigated. The results show that by the annealing at 650 °C and in the first training cycle, the condition is best for the formation of highest stress-induced ɛ martensite and the maximum SME is obtained at this temperature. This can be attributed to the optimum austenite grain size and also sufficient numbers of crystallographic defects such as Shockley partial dislocations in the microstructure. With repeating the training cycles, SME increases at all annealing temperatures especially at annealing temperature of 550 °C, because of increase in the stacking faults in the microstructure that contribute to increase strength of matrix. In the specimens annealed at higher temperatures, the reverse ɛ → γ transformation to result in SME decreases because of the presence of stress-induced ά martensite that retards reverse motion of Shockley partial dislocations. Other results illustrate that pseudoelasticity effect decreases with increasing annealing temperature because of a reduction in reverse ɛ → γ transformation during unloading due to increase in the stress needed for reverse transformation.