Influence of annealing time on shape memory effect of an Fe-Mn-Si based alloy during thermo-mechanical treatment

Abstract

The shape memory effect of Fe-Mn-Si based alloys could be significantly improved by thermo-mechanical treatments. In this work, the cast Fe-Mn-Si based alloy was hot forged, 20% cold rolled and solution treated, followed by annealing at 1073 K for different time on some specimens deformed by 10% at room temperature, and the effect of annealing time of thermo-mechanical treatments on the microstructures and shape memory effect of the Fe-Mn-Si based alloy was studied with the help of backscattered electron microanalysis (EBSD), RGM-4300 universal testing machine, differential four-terminal resistance method and bending method.Results show that the recovery strain of the solution-treated Fe-Mn-Si based alloy is 4.1%; when the annealing time of thermo-mechanical treatment is 10 min, the recovery strain is remarkably improved to 5.3%; As the annealing time of thermo-mechanical treatment is further prolonged, the recovery strain decreases; when the annealing time of thermo-mechanical treatments is 180 min, the recovery strain decreases to 4.9%. As the annealing time of thermo-mechanical treatments prolongs, the fraction of annealing twins increases, while the density of stacking faults decreases, which leads to the ability of facilitating stress-induced ε martensitic transformation and suppressing plastic glide weakening. This is the main reason why the recovery strain of the Fe-Mn-Si based alloy decreases with the annealing time of thermo-mechanical treatments prolonging.

Keywords

• shape memory alloys
• thermo-mechanical treatment
• annealing twins
• stacking fault