Superelasticity and shape memory effects in polycrystalline Ni–Mn–Ga microwires

Non-stoichiometric Ni49.9Mn28.6Ga21.5 microwires with a diameter of 30–80 μm and cellular grain size of 1–3 μm were developed by melt-extraction. The superelasticity and shape memory effect of the microwires were investigated on a Dynamic Mechanical Analyzer (DMA Q800). The onset critical stresses for austenite to martensite transformation increase linearly with temperature and can be described by Clausius–Clapeyron relationship. The martensite to austenite transformation upon unloading only at temperatures at least 11 °C higher than the martensite start temperature. The as-extracted microwire was loaded in its martensite state to a strain of 2.7% without breaking and 92% plastic deformation strain recovers upon heating.

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► We prepared fine-grained Ni–Mn–Ga microwires by melt-extraction.
► The microwires have enhanced superelasticity and shape memory properties than bulk samples.
► The superelastic stress follows the Clausius–Clapeyron relationship with a slope of 8.7 MPa/°C.
► The microwire recoveres 92% of its plastic deformation strain upon heating.