Effects of thermo-mechanical treatment on a Fe–30Mn–6Si shape memory alloy

Effects of thermo-mechanical treatment on a Fe–30Mn–6Si shape memory alloy were investigated, including the microstructure, precipitation behavior and shape memory performance. Experimental results show that the as-cold-rolled specimen exhibits a worse shape recovery, and its Ms temperature and transformational enthalpy (ΔH) are much lower than those of as-annealed one. Specimens with 10% cold-rolling and subsequent 550–650 °C aging have lots of (Fe, Mn)3Si precipitates within the grain interior. These precipitates exhibit a D03 structure with lattice constant of 5.66 Å, and show a near orientation relationship with γ austenite as [1¯ 1 1]D03//[0 1 1]γ, (2¯ 0 2¯)D03//(1¯ 1¯ 1)γ. The 550–650 °C aged specimen can exhibit high shape recovery ratios, due to the contributions of effective nuclei and well-aligned precipitates within the grain interior. If the aging temperature is higher than 750 °C, the recrystallization occurs and the disappearance of both effective nuclei and well-aligned precipitates within the grain interior will obviously reduce the specimen's shape memory performance.