| 1. |
- Cong, D. Y., et al.
(författare)
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Neutron diffraction study on crystal structure and phase transformation in Ni-Mn-Ga ferromagnetic shape memory alloys
- 2007
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Ingår i: Powder Diffraction. - : Cambridge University Press (CUP). - 0885-7156 .- 1945-7413. ; 22:4, s. 307-311
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Tidskriftsartikel (refereegranskat)abstract
- Crystal structure and phase transformation behaviors in two Ni-Mn-Ga ferromagnetic shape memory alloys (FSMAs) with compositions of Ni48Mn30Ga22 and Ni53Mn25Ga22 (at. %) as a function of temperature were investigated by in situ neutron diffraction experiments. Neutron diffraction technique proves to be highly efficient in characterizing structural transformation in Ni-Mn-Ga FSMAs, which consist of nearby elements in the periodic table. Our neutron results show that Ni48Mn30Ga22 has a cubic, L-21 Heusler structure from 373 to 293 K. Its crystal structure changes into a seven-layered orthorhombic martensitic structure when cooled to 243 K, and no further transformation is observed upon cooling to 19 K. Neutron diffraction results also show that Ni53Mn25Ga22 has a tetragonal 14/mmm martensitic structure from 20 to 403 K. A pre-transformation around room temperature is observed from an abrupt jump in unit-cell volume of Ni53Mn25Ga22, which corresponds with an endothermic peak detected in a heated DSC curve.
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| 2. |
- Peng, Ru, 1960-, et al.
(författare)
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Crystal structure and phase transformation in Ni53Mn 25Ga22 shape memory alloy from 20 K to 473 K
- 2005
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 87:11
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Tidskriftsartikel (refereegranskat)abstract
- The crystal structures, magnetic structures, and phase transformation of the off-stoichiometric Ni53 Mn25 Ga22 were studied by neutron powder diffraction at different temperatures. It is shown that Ni53 Mn25 Ga22 has a tetragonal I4/mmm structure from 20 K to 403 K. An abrupt jump in unit-cell volume around room temperature, corresponding to an endothermic peak in the differential scanning calorimetry curve, was observed. This indicates a pretransformation in the martensitic phase of Ni53 Mn25 Ga22, which is completely different from the phase transformation in the stoichiometric Ni2 MnGa. The sequence of structural transformation in Ni53 Mn25 Ga22 is closely related to its intrinsic temperature-dependent magnetic structure. © 2005 American Institute of Physics.
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| 3. |
- Wang, Y.D., et al.
(författare)
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Textures and compressive properties of ferromagnetic shape-memory alloy Ni48Mn25Ga22Co5 prepared by isothermal forging process
- 2006
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Ingår i: Journal of Materials Research. - : Springer Science and Business Media LLC. - 0884-2914 .- 2044-5326. ; 21:3, s. 691-697
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Tidskriftsartikel (refereegranskat)abstract
- A ferromagnetic shape-memory alloy Ni48Mn25 Ga22CO5 was prepared by the induction melting and isothermal forging process. Dynamic recrystallization occurs during the isothermal forging. The deformation texture was studied by the neutron diffraction technique. The main texture components consist of (110) [11¯2] and (001) [100], which suggested that in-plane plastic flow anisotropy should be expected in the as-forged condition. The uniaxial compression fracture strain in the forged alloy reaches over 9.5%. The final room-temperature fracture of the polycrystalline Ni48Mn25Ga22CO5 is controlled mainly by intergranular mode.
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| 4. |
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| 5. |
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| 6. |
- Cong, D Y, et al.
(författare)
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Crystal structures and textures in the hot-forged Ni-Mn-Ga shape memory alloys
- 2006
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Ingår i: Metallurgical and Materials Transactions. A. - 1073-5623 .- 1543-1940. ; 37A:5, s. 1397-1403
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Tidskriftsartikel (refereegranskat)abstract
- Three ferromagnetic shape-memory alloys with the chemical compositions of Ni53Mn25Ga22, Ni48Mn30Ga22, and Ni48Mn25Ga22Co5 were prepared by the induction-melting and hot-forging process. The crystal structures were investigated by the neutron powder diffraction technique, showing that Ni53Mn25Ga22 and Ni48Mn25Ga22Co5 have a tetragonal, I4/mmm martensitic structure at room temperature, while Ni48Mn30Ga22 has a cubic, L2(1) austenitic structure at room temperature. The development of textures in the hot-forged samples shows the in-plane plastic flow anisotropy from the measured pole figures by means of the neutron diffraction technique. Significant texture changes were observed for the Ni48Mn25Ga22Co5 alloy after room temperature deformation, which is due to the deformation-induced rearrangements of martensitic variants. An excellent shape-memory effect (SME) with a recovery ratio of 74 pct was reported in this Ni48Mn25Ga22Co5 polycrystalline alloy after annealing above the martensitic transformation temperature, and the "shape-memory" influence also occurs in the distributions of grain orientations.
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| 7. |
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