Influence of Fe on shape memory effect of Ni-Mn-Ga alloy microwire

The shape memory effect of alloy microwire with Fe replacing Ga based on Ni-Mn-Ga alloy microwire was analyzed. Ni-Mn-Ga-Fe alloy was prepared by vacuum tungsten arc melting furnace and the parent alloy was prepared by a high vacuum precision melt drawing equipment. The effects of Fe doping on the phase, the martensite transition behavior, and shape memory effect were studied by EDS, DSC, XRD and DMA. The results show that the Ni-Mn-Ga-Fe alloy microwire shows the mixed phase of tetragonal martensite phase and face-centered cubic austenitic phase. The step ordering heat treatment was used for the microwire. The microwire was treated by step-by-step step ordering heat treatment, the ordered heat treatment can effectively reduce the internal defects of the microwires, release the internal stress, refine the internal grains of the microwire, shrink the lattice volume, improve the compactness of the microwire, and make the martensite twin interface more straight and easier to move, and improve the elongation of the microwire.The one-way shape memory test of the prepared Ni-Mn-Ga-Fe alloy microwires is carried out at 258 K, after stretching to 350 MPa and unloading to 0 MPa. The strain recovery rate is 78.75% after the microwires are heated to the austenite state. The one-way shape memory test of the ordered heat-treated Ni-Mn-Ga-Fe alloy microwires is carried out at 289 K, and the strain recovery rate reaches 100%. The ordered heat-treated ternary Ni-Mn-Ga alloy microwire and Ni-Mn-Ga-Fe alloy microwire are stretched under constant stress at 126 MPa and 240 MPa, respectively. The two-way shape recovery ability of the two microwires can reach almost 100%, but the phase transition width of the alloy microwire during deformation, namely the elastic strain energy storage is more than that of the ternary alloy microwire. The addition of Fe makes the mechanical properties of the alloy microwires higher than that of the traditional ternary shape memory alloy microwire; compared with Ni-Mn-Ga alloy microwires, the martensitic transformation temperatures of Ni-Mn-Ga-Fe alloy microwires in as-prepared and heat-treated states increase by 6.0 K and 11.5 K respectively, and the thermal hysteresis decreases by 6.7 K and 1.5 K respectively. In practical applications, Ni-Mn-Ga-Fe shape memory alloy may be more widely used due to its small thermal hysteresis, high martensitic transformation temperature and large strain recovery rate.