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. DOI:10.1088/0964-1726/22/3/035008 · 2.45 Impact Factor
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ABSTRACT: The effect of Y addition on the average grain size and mechanical properties of Ni-Mn-Ga magnetic shape memory alloys is researched by means of optical microscope, compressive test and scanning electron microscope (SEM) in the paper. The results show that Y addition refines the grains of Ni-Mn-Ga alloy significantly and significantly enhances the compressive strength and maximum compressive strain. In addition, the fracture type changes from typical intergranular crack to transgranular crack gradually with Y addition.07/2011; 299-300:645-648. DOI:10.4028/www.scientific.net/AMR.299-300.645
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ABSTRACT: The microstructures, martensitic transformation, mechanical and shape memory properties of (Ni53Mn22Co6Ga19)(100-x)Y-x (x = 0, 0.1, 0.3) high-temperature shape memory alloys were investigated. It was found that small Y addition results in the refinement of grain size and the increase of gamma phase volume fraction. These changes can effectively improve the tensile ductility and fracture strength of two-phase Ni53Mn22Co6Ga19 alloy, up to the maximum values of 10.1 % and 592 MPa respectively at x = 0.1. However, it is proposed that Y(Ni,Mn)(4)Ga precipitate forms in the alloys with the addition of Y, and its amount increases with further increasing Y addition. The growth of the Y(Ni,Mn)(4)Ga precipitate results in a decrease in the tensile ductility at x = 0.3. Results further show that shape memory properties of the studied alloys are closely related to the refinement of grain size and the alloy yield strength. While adding 0.1 at.% of Y, the shape memory effect and recovery rate decrease, resulting from the refinement of grain size, compared to those of two-phase Ni53Mn22Co6Ga19 alloy. Subsequently they increase with further increasing Y content to 0.3 at.% due to the decrease in the alloy yield strength.International Journal of Materials Research (formerly Zeitschrift fuer Metallkunde) 01/2014; 105(1):83-88. DOI:10.3139/146.110993 · 0.68 Impact Factor