Martensitic Transformation And Stress Analyze Of Ni-Mn-Ga Magnetic Shape Memory Alloys

The characteristics of martensitic transformation, mechanical property of martensite and crystal structure in Ni_52.2Mn_24.4Ga_23.4 single crystal were investigated by means of resistivity measurement, strain measurement, optical microstructure, nanoindention technique and X-ray diffraction etc.; the crystallography data was acquired by applying phenomenological theory of martensite crystallography to Ni_52.2Mn_24.4Ga_23.4 alloy; this article not only computes martensite transformation stress and energy, but also discusses the effect of several parameters on them and the effection of stress on Ni_52.2Mn_24.4Ga_23.4 performance.Martensite transformation hysteresis is narrow in Ni_52.2Mn_24.4Ga_23.4 single crystal, the transformation is completely and martensitic variants have the same orientation. The dilatation strain is occurred during martensite transformation and the contraction strain during reverse transformation.X-ray diffraction spectrum of L2₁ structure accords with that of face-centered cubic structure; Martensite is body-centered tetragonal structure (5M). The lattice parameter of austenite and martensite are: a₀=0.582 nm; a_M=b_M=0.591 nm, c_M=0.557 nm.The average elastic modulus of two martensite variants is 82.15 GPa and 88.0 GPa respectively; the average hardness is 3.91 GPa and 3.60 GPa respectively. The mechanical properties are different between the two martensite variants, even in different place of a single variant.Habit plane is parallel to [-0.02345 -0.000192 -0.02594], total transformation strain is 0.075581, shear strain and contraction strain were 0.074858 and -0.010424 respectively in the martensitie transformation of Ni_52.2Mn_24.4Ga_23.4 alloy. The results show that: when assuming that the plane and direction of the lattice-invariant shear are (1 1 0) and [1 1 0] respectively, the orientation relationship between parent and martensite are...