Effect of chemical ordering annealing on superelasticity of Ni–Mn–Ga–Fe ferromagnetic shape memory alloy microwires**Project supported by the National Natural Science Foundation of China (Grant Nos. 51701099, 51801044, and 51671071), the Natural Science Foundation of Heilongjiang Province of China (Grant No. LH2019E091), and Fundamental Research Funds in Heilongjiang Provincial Universities, China (Grant No. 135409320). Thanks to the help of Technology Innovation

Abstract

Ni50Mn25Ga20Fe5 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 Ni50Mn25Ga20Fe5 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.