Effect of rare earth Dy addition on microstructure and martensitic transformation of polycrystalline Ni50Mn29Ga21−xDyx ferromagnetic shape memory alloys
ABSTRACT The effects of rare earth Dy addition on microstructure and martensitic transformation of polycrystalline Ni50Mn29Ga21−xDyx (numbers indicate at.%) shape memory alloys were investigated by means of scanning electron microscopy, energy dispersive X-ray spectroscopy, differential scanning calorimetry and X-ray diffraction. The results show that the microstructure of Ni–Mn–Ga–Dy alloys consists of the matrix and Dy-rich phase. Small amounts of the Dy-rich phase with 0.1 at.% Dy disperse homogeneously in the matrix. With the increase of the Dy content, the Dy-rich phase becomes larger and trends to distribute along the grain boundaries. The one-step martensitic transformation is observed in Ni50Mn29Ga21−xDyx alloys. With increasing Dy content, the martensitic transformation temperatures of Ni50Mn29Ga21−xDyx alloys increase remarkably, whereas the martensite structure of the Dy-containing alloys appears to be unchanged exhibiting seven-layered martensite structures at room temperature.
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ABSTRACT: The effects of Dy addition on microstructure, martensitic transformation, mechanical and shape memory properties of the two-phase Ni53Mn22Co6Ga19 high-temperature shape memory alloy were investigated. It is found that a small Dy addition results in the refinement of grain size, which can effectively improve the tensile ductility and strength of the two-phase Ni53Mn22Co6Ga19 alloy. However, a Dy(Ni,Mn)4Ga precipitate forms in the alloys with the Dy addition, and its amount increases with an increase in the Dy addition. This change causes the ductility of the alloys to decrease when the Dy addition is further increased to 0.3 at.%. The results further show that the changes in the martensitic transformation temperature of the studied alloys can be attributed to the combined effects of the tetragonality (c/a) and electron concentration (e/a) of martensite. Additionally, the shape memory effects of the alloys are closely related to the refinement of grain size and the alloy strength. In this study, the (Ni53Mn22Co6Ga19)99.8Dy0.2 alloy exhibits a variety of good properties, including a high martensitic transformation starting temperature of 385.7 °C, a tensile ductility of 10.3% and a shape memory effect of 2.8%.Smart Materials and Structures 02/2013; 22(3):035008. · 2.02 Impact Factor