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Effect of rare earth Dy addition on microstructure and martensitic transformation of polycrystalline Ni50Mn29Ga21−xDyx ferromagnetic shape memory alloys

School of Materials Science and Engineering, P.O. Box 405, Harbin Institute of Technology, Harbin 150001, China
Materials Science and Engineering A (Impact Factor: 2.57). 11/2006; 438:1077-1080. DOI: 10.1016/j.msea.2006.02.190

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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    • "Recently it has been reported that the phase transition temperatures can also be manipulated by the addition of rare earth (RE) elements [25e33]. It was found that the solid solubility of the large size RE atoms were quite low in the as-cast alloys due to the low solidification rate [26] [28] [31]. Therefore, the micron-sized RE-rich precipitates are formed in the as-cast samples and the matrix is still kept as ternary NieMneGa compositions. "
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    ABSTRACT: Ni50Mn29Ga21-xTbx (x=0-1) ribbons with the solid solution of Tb element were synthesized by the melt spinning method. The phase transformation, magnetic properties and magnetocaloric effect were investigated. With the increasing Tb content the martensitic transformation temperatures were gradually increased while the Curie temperature was monotonously decreased. According to the detected phase transition temperatures, a phase diagram was established to describe the dependence of the magneto-structural transition on the Tb content. Three types of magneto-structural transitions were observed. Especially, the martensitic transformation was coincided with the magnetic transition in the single phase alloy with x = 0.1, giving rise to the coupled magneto-structural transition from ferromagnetic martensite to paramagnetic austenite. Sizable magnetic entropy change of 4.31 J/Kg K was induced from the coupled magneto-structural transition by the application of magnetic field of 50 kOe at 349.5 K.
    Full-text · Article · Feb 2016 · Intermetallics
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    • "It can be seen that the reversible martensitic transformation temperatures abruptly increase (as high as 17 • C for M p ) at x = 0.1. But on further increasing the Dy content to 0.3 at.%, they only increase slightly (by 5.7 • C for M p ). Similar observations are observed in the previous investigations [18] [19]. "
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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%.
    Full-text · Article · Feb 2013 · Smart Materials and Structures
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    ABSTRACT: The effect of rare earth Y on the microstructure, martensitic transformation and mechanical properties of Ni50Mn28Ga22−xYx alloys was investigated. The addition of Y results in a change in the microstructure and crystal structure. One-step thermoelastic martensitic transformation is observed in Ni50Mn28Ga22−xYx alloys. The martensitic transformation temperature notably increases with the increase in Y content. It is found that the addition of Y significantly improves the compressive ductility of the alloys.
    No preview · Article · Oct 2007 · Scripta Materialia
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