| Recent years much attention has been directed to the ferromagnetic shape memory alloys (FSMAs) Ni-Mn-In due to the novel characteristics arising from the magnetostructural coupling between the first-order-type structural and second-order-type magnetic transition. With the purpose of exploring new Ni-Mn-In FSMAs and improving the properties of Ni-Mn-In FSMAs, in this paper, we prepared the doping Ni-Mn-In-X alloys by arc-melting and melt-spinning method. We systemically investigated the the structure, phase transition as well as the magnetic properties of these alloys through X-ray diffraction, Physical Property Measurement System and Scanning Electron Microscope. The main content is as following:(1) Since ferromagnetic shape memory effect for Ni-Mn-In system is only observed in Mn-rich composition, in this paper, we prepared Ni-rich Ni5o+xMn25ln25-x (x=0,1,2,3,4,5and6) alloys and investigated the discipline of martensitic transformation among them. We found that the martensitic transformation began to appear from x=5with the decreasing lattice constant. Considering the critical lattice parameter of Ni2Mn1+xIn1-x from first-principle calculations and martensitic transformation discipline of Ni5oMn5o-xInx (15≤x≤16), we came to the conclusion that cell volume change was the dominant factor to induce MT in Ni-Mn-In, that was the lattice constant must lie in a critical range(a<0.601nm) if Ni-Mn-In appear martensitic transformation.(2) During the study of Ni-rich Ni50+xMn25ln25-x (x=0,1,2,3,4,5and6) alloys, we found Ni55Mn25In20with highly textured flakes emerged thermoelastic martensitic transformation from the ferromagnetic parent phase to the ferromagnetic martensite phase. In order to find out the mechanism of martensitic transformation, we investigated the microstucture, magnetic and martensitic properties of the alloy. A magnetization change of about9emu/g across phase transformation was observed and the martensitic transformation temperature was decreased by about9K by the application of a magnetic field of5T. So magnetic field-induced martensitic transformation can be expected from this alloy.(3) We choose Ni50Mn33In17as the parent matrix which does not appear martensitic transformation and substitute In with Ga in Ni50Mn33In17-xGax system with constant value of e/a. We investigated the effects of substitution on the structure, phase transition as well as the magnetic properties in these alloys. With the increase of Ga content, the cell volume decreases. Although martensitic transformation does not appear in Ni50Mn33In17, martensitic transformation begin to occur from Ni50Mn33In14Ga3(a<0.601nm) with the increasing Ga content, implying that cell volume change is the dominant factor to induce martensitic transformation in our system considering the e/a is a constant. This is in accordance with the result of Ni-rich Ni50+xMn25In25-x (x=0,1,2,3,4,5and6) alloys. Furthermore, in the absence of prestrain, a large reversible magnetic field-induced strain of about0.22%was observed in Ni50Mn33In12Ga5at7T, exhibiting a good two-way metamagnetic shape memory effect.(4) The temperature and magnetic field-induced transformation strain has been investigated in polycrystalline Ni50Mn36In14-xSbx (x=0,2,4,6). Partial substitution of Sb for In leads to a large increase of transformation strain, up to1.7%in nonprestrained Ni50Mn36IngSb6, which is about more than ten times larger than that in Sb-free Ni-Mn-In. In addition, the same value of magnetic field-induced strain is observed due to the magnetic field-induced martensite-austenite transformation. This behavior can be attributed to the highly preferred crystallographic orientation and the change of martensitic structure. |
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