Effect of chemical ordering annealing on superelasticity of Ni–Mn–Ga–Fe ferromagnetic shape memory alloy microwires*

Abstract

Ni 50 Mn 25 Ga 20 Fe 5 ferromagnetic shape memory alloy microwires with diameters of ∼ 30–50 μm and grain sizes of ∼ 2–5 μm were prepared by melt-extraction technique. A step-wise chemical ordering annealing was carried out to improve the superelasticity strain and recovery ratio which were hampered by the internal stress, compositional inhomogeneity, and high-density defects in the as-extracted Ni 50 Mn 25 Ga 20 Fe 5 microwires. The annealed microwires exhibited enhanced atomic ordering degree, narrow thermal hysteresis, and high saturation magnetization under a low magnetic field. As a result, the annealed microwire showed decreased superelastic critical stress, improved reversibility, and a high superelastic strain (1.9%) with a large recovery ratio (> 96%). This kind of filamentous material with superior superelastic effects may be promising materials for minor-devices.