21 July 2004 Microstructure and solidification behavior of Ni-Mn-Ga magnetic shape memory alloys
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In order to understand the solidification behavior of Ni-Mn-Ga alloys, ingots with different compositions were prepared by arc melting. Two series of compositions were investigated: Ni100-2xMnxGax (15≤x ≤30) and Ni50Mn50-yGay (0≤y≤50). The microstructures obtained were observed and the compositions of the phases occurring in the ingots were identified by energy dispersive spectroscopy in the scanning electron microscope. Based on these observations, three solidification paths were identified: direct solidification of γ-Ni from the liquid, direct solidification of β-NiMnGa from the liquid, and solidification of β-NiMnGa phase via a peritectic reaction. It was found that the γ-Ni liquidus surface covers a large area of the ternary phase diagram. The γ-Ni liquidus boundary is located between Ni50Mn25Ga25 and Ni45Mn27.5Ga27.5 in the equal Mn and Ga alloy series, and between Ni50Mn5Ga45 and Ni50Mn10Ga40 in the 50 at.% Ni alloy series. The alloys with compositions close to the stoichiometric Ni2MnGa composition that show the magnetic shape memory effect are all covered by the γ-Ni liquidus surface. The β-NiMnGa liquidus surface covers the remaining alloy compositions.
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Jian Chen, Jian Chen, Michael A. Gharghouri, Michael A. Gharghouri, Calvin V. Hyatt, Calvin V. Hyatt, } "Microstructure and solidification behavior of Ni-Mn-Ga magnetic shape memory alloys", Proc. SPIE 5387, Smart Structures and Materials 2004: Active Materials: Behavior and Mechanics, (21 July 2004); doi: 10.1117/12.540752; https://doi.org/10.1117/12.540752

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