Abstract:
The effect of chemical composition on the microstructure, high-temperature superelasticity and strength properties of martensite has been studied on Ni$_2$MnGa-Fe polycrystals. Ni$_{52}$Mn$_{17}$Ga$_{21}$Fe$_{10}$ and Ni$_{56}$Mn$_9$Ga$_{19}$Fe$_{16}$ (at.%) alloys contain a large amount of $\gamma$-phase (from 25 to 60%), which prevents the superelasticity. The high-temperature superelasticity was found in Ni$_{56}$Mn$_{10}$Ga$_{25}$Fe$_9$ polycrystals without $\gamma$-phase under compression. Change from polycrystals to single crystals (in alloy of close composition Ni$_{54}$Mn$_{12}$Ga$_{25}$Fe$_9$) results in a significant increase in the strength properties of martensite from 720 to 1450 MPa due to the choice of the compression axis along the high-strength [001]-direction while maintaining the plasticity of 19% and high-temperature superelasticity.
Keywords:Heusler alloys, martensitic transformation, high-temperature superelasticity, nimngafe, single crystals, $\gamma$-phase.
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