Significant enhancement of shape recovery and pseudoelasticity in an intercritically-annealed Fe–Ni–Mn alloy through cold rolling

This research was conducted to study the effects of cold rolling by 20 %, 40 %, and 60 % reductions in thickness on the microstructure, mechanical properties, and shape memory behaviors of an intercritically-annealed Fe-9.6Ni-7.1Mn (at.%) alloy with an initially martensitic microstructure. Microstructural characterizations revealed that the microstructure of the intercritically-annealed (IA) specimen at 620 °C for 1.2 ks consisted of the lath alphaperime-martensite (α′-martensite) and reversed gamma-austenite (γ-austenite). After cold rolling of the IA-specimen, the microstructure included three phases of α′-martensite, austenite, and epsilon-martensite (ε-martensite) due to the occurrence of the γ→ε→α′ transformation. By increasing the cold rolling percent, the fractions of austenite and ε-martensite decreased so that more than 95 % of the microstructure was the α′-martensite in the 60 % cold rolled (CR) sample. Tensile testing showed a proper combination of a relatively high ultimate tensile strength of ∼1020 MPa and good ductility of ∼11.8 % MPa in the 40 % CR sample that the former was due to a considerable increase in density of dislocations under straining, and the latter was associated with the existence of a proper fraction of the austenite in the microstructure. The relatively high strength of the 40 % CR sample led to the observation of a maximum shape recovery of ∼43 % for this sample compared to the small amount of ∼5 % in the IA specimen at the same pre-strain of 4 %. Also, a maximum pseudoelasticity of ∼45 % was calculated for the 40 % CR sample due to the existence of a proper fraction of the deformation-hardened austenite in microstructure.