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Study Of Structures And Performances Of Ni51Mn27Ga22 And Ni45Co5Mn36.6In13.4 Ferromagnetic Shape-Memory Alloys And Composites

Posted on:2010-01-26Degree:MasterType:Thesis
Country:ChinaCandidate:G S ZhouFull Text:PDF
GTID:2211330368499839Subject:Materials science
Abstract/Summary:PDF Full Text Request
Ferromagnetic shape memory alloys Ni-Mn-Ga/Ni-Mn-In have drawn considerable attentions due to their colossal magnetic-field-induced strains (MFIS). However, the intrinsic brittleness of polycrystalline alloys has always been a problem for practical applications. Single crystals are relatively ductile and are often ideal for MFIS, but single crystals are of high cost and not easy in shaping. What's more, in polycrystalline, the MFIS would often be blocked by the incompatible grain boundaries. To overcome these problems, the polymer-bonded composite is proposed.In this thesis, two different alloys Ni51Mn27Ga22 and Ni45Co5Mn36.6In13.4 were chosen to prepare the polymer-bonded composites. The high-energy ball-milling method was used to prepare the alloy powders. After ball-milling and annealing, the alloy powders were mixed with the self-ductility epoxy resin and cure at a certain temperature to prepare composites. Successfully, the polymer-bonded Ni51Mn27Ga22 and Ni45Co5Mn36.6In13.4 composites were prepared with enhanced plasticity. During the whole experiment, the metallographic, differential scanning calorimeter (DSC) and X-ray powder diffraction (XRD) techniques are used to investigate the martensitic transformation behaviors and microstructural characteristics of the two alloys at different forms; The stress-induced reorientation of martensitic variants and stress-induced martensitic measurements before and after compression. The properties of the magnetic-field-induced strain within the composites are also confirmed.The results are summarized as follows:Before ball-milling,the Ni51Mn27Ga22 alloy has the non-modulated body-centered tetragonal martensite structure at room temperature, after ball-milling for 20 mins and annealing, the structure of the obtained powders changes to modulated martensite structure.The Ni45Co5Mn36.6In13.4 alloy has the mixed structure of seven-layered modulated martensite and the parent phase before ball-milling, after ball-milling for 20mins and annealing, the obtained powder changes to the parent structure.The two kinds of obtained powders were mixed with the self-ductility epoxy resin to prepare composites. Successfully, the polymer-bonded Ni51Mn27Ga22 and Ni45Co5Mn36.6In13.4 composites were prepared with enhanced plasticity. At room temperature, the resin composite is of modulated martensite structure, and the resin composite is of the parent phase structure. The stress-induced reorientation of martensitic variants is confirmed within the Ni51Mn27Ga22-epoxy resin composite,whereas the stress-induced martensitic phase transformation is confirmed within the Ni45Co5Mn36.6In13.4-epoxy resin composite. After unloading, the Ni51Mn27Ga22-epoxy resin composite retains 3% strain, and a magnetic field could induce 2% recovery strain;the Ni45Co5Mn36.6ln13.4-epoxy resin composite retains 1.8% strain, and a magnetic field could induce 1% recoverystrain. The prepared Ni45Co5Mn36.6In13.4-epoxy resin composite has a considerable magnetic-field-induced strain, and its plastic has been greatly improved.
Keywords/Search Tags:Ferromagnetic shape memory alloys, composite, magnetic-field-induced strains, martensitic transformation, martensitic variant reorientation
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