Microstructure,phase transformation and mechanical property of Nb-doped Ni–Mn–Ga alloys |
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| Affiliation: | 1. Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China;2. German Engineering Materials Science Centre (GEMS), Helmholtz-Zentrum Geesthacht (HZG) Outstation at FRM II, Garching D-85748, Germany;3. Laboratoire d''Étude des Microstructures et de Mécanique des Matériaux (LEM3), CNRS UMR 7239, Université de Lorraine, Metz 57045, France;1. Lappeenranta University of Technology, Material Physics Laboratory, Laitaatsillantie 3, FI-57170 Savonlinna, Finland;2. Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 1999/2, CZ-182 21 Prague, Czech Republic;3. Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 5, CZ-12116 Prague, Czech Republic;1. Basque Center for Materials, Applications and Nanostructures (BCMaterials), UPV/EHU Science Park, Leioa, Spain;2. University of the Basque Country (UPV/EHU), Campus of Leioa, Leioa, Spain;3. Ikerbasque, Basque Foundation for Science, Bilbao, Spain;4. Taras Shevchenko National University of Kyiv, Kyiv, Ukraine;5. Institute of Magnetism NASU and MESU, Kyiv, Ukraine;6. Departament de Física, Universitat de les Illes Balears, Palma de Mallorca, Spain |
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| Abstract: | This study investigated the microstructure, phase transformation and mechanical property of (Ni49.8Mn28.5Ga21.7)100-xNbx (x = 1, 3, 6, 9) alloys. The Nb1 alloy exhibited a single austenite phase at room temperature. With increasing Nb content for Nb3, Nb6 and Nb9, the alloy changed to a dual phase consisting of austenitic matrix and Nb-rich second phase with a hexagonal structure, and the amount of the second phase increased with the increase of Nb content. The martensitic transformation temperature and Curie temperature were changed and the transformation enthalpy was gradually reduced with increasing Nb content. The change of martensitic transformation temperature and Curie temperature was related to the introduction of Nb in the Ni–Mn–Ga structure that decreased valence electron concentration (e/a), increased unit cell volume and reduced magnetic exchange of the alloys. The decrease of transformation enthalpy was mainly attributed to the formation and increase of the Nb-rich second phase that reduced volume fraction of the matrix taking part in phase transformation. All the alloys presented a similar compression behavior with progressively fracturing characters (occurrence of several stress drops before complete fracturing). The fracture strength was slightly enhanced with increasing Nb content from Nb0 to Nb9, but the ductility has no apparent improvement. |
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| Keywords: | A Shape-memory alloys B Brittleness and ductility B Martensitic transformation B Mechanical properties D Microstructure |
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