The martensitic and magnetic transformations, as well as the mechanical properties, of Ni₂MnAl alloys in as-cast (AC) and heat-treated (HT) conditions were investigated. Magnetic-field-induced strain was evaluated via magnetostriction, with reversible strains of 0.14% and 0.2% achieved in the martensitic phase at 2 K for the AC and HT alloys, respectively. Transformation temperatures and Curie temperatures were determined under constant applied magnetic field, revealing that γ-phase inclusions in the AC microstructure suppress antiferromagnetic domain response, yielding a lower magnetization (∼8.4 emu g⁻¹) compared to the HT alloy (∼13.4 emu g⁻¹). Both alloys exhibited hysteretic behavior in the martensitic state and a linear, paramagnetic response in the austenitic state. Mechanical testing showed predominantly brittle fracture in the AC alloy, while the HT alloy displayed a yield point and Lüders band behavior, indicating limited ductility. Ultimate tensile strength, yield strength, fracture strain, and hardness were quantified for both conditions, demonstrating the combined influence of microstructure, magnetic response, and mechanical behavior. These results highlight Ni₂MnAl as a promising candidate for magnetic-field-controlled shape memory applications, with tunable mechanical and functional properties via heat treatment. • Demonstrated that the presence of secondary gamma phase in the alloy matrix inhibits magnetic properties and lowers the degree of response of shape memory. • Reversible strain of 0.2% was achieved in the single phase sample up to fields of 9 T comparable to the strains obtained in NiMnGa SMA up to fields of 8 T. • Magnetic behavior of the alloys in the martensite and Austenite temperature range have been demonstrated. • Thermal expansion coefficient of the alloy has been determined and could possibly be an indicator of the presence of a phase change in the alloy. • Mechanical properties have been determined, and this is the first reporting of the tensile data on NiMnAl SMA.
Daches et al. (Mon,) studied this question.