An origin of superelasticity in Fe–Mn–Al–Ni alloy: A phase-field study

Phase-field simulations are performed to investigate the martensitic transformation (MT) from body-centered-cubic-α to face-centered-cubic-γ′ when external compressive stress is applied along the [100] α direction, as well as the reverse MT from γ′ to α during the unloading of the external stress. The objective is to gain fundamental insights into the reversibility of the MT in Fe–Mn–Al–Ni alloy with a microstructure containing nanoscale β-NiAl precipitates in the α phase. The stress-induced MT from α to γ′ occurred under a compressive loading of approximately 400 MPa, resulting in a martensite microstructure composed of two of the three crystallographic orientation variants. The elastic energy in the β phase increased owing to the MT, which slightly increased the structural density of martensite and consequently increased the chemical free energy of the β phase. Moreover, the structural density of martensite in the γ′ phase decreased near the β-phase boundary, where a compositional gradient was present, resulting in an increase in the chemical free energy of the γ′ phase. A complete reverse MT occurred when the total free-energy change, determined by the balance between the elastic-energy change and chemical free-energy change, temporarily became positive during the unloading of external stress.