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Martensitic Transformation Behavior And Structure And Properties Of Ni-Mn-In Based Alloys

Posted on:2010-08-17Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y FengFull Text:PDF
GTID:1101360332957826Subject:Materials Physics and Chemistry
Abstract/Summary:PDF Full Text Request
The martensitic transformation behavior, microstructures and properties of Ni-Mn-In based alloys have been investigated systematically by means of SEM, TEM, XRD, DSC, compressive tests, AC susceptibility, PPMS and transformation strain measurements. The influence and mechanics of In content, Co and Fe doping on phase constitute, phase transformation, mechanical properties and magnetic properties are illuminated.The research found that the Ni50Mn50-xInx(x=16, 15, 14, 13, 12) alloys are single solid solution. The phase constitute of Ni-Mn-In alloy is changed by doping Co and Fe element: As the Co content is 3at.% or Fe content is 5at.%, there are short stick-like Co-rich or Fe-rich fccγphase in matrix, and the demention and volume fraction ofγphase increase with the increase of Co or Fe content.The experimental results indicate that the Ni50Mn50-xInx alloys undergo thermal-elastic martensitic transformation and inverse phase transformation as cooling or heating. As In content is 15at.%, the martensite is monoclinic 5M modulated structure. As In content is 13at.%, the martensite becomes monoclinic 7M modulated. As In content is 12at.%, the martensite is monoclinic 7M modulated with few unmodulated structure. As In content is 14at.%, the alloy undergoes two-step transformation from cubic L21→orthogonal 4O→monoclinic 7M modulated structure. The relationship between variants is mainly (102)M I-type twin. Ni50Mn34In16-yCoy(y=0, 2, 3, 4, 5, 8) and Ni50Mn34In16-yFey(y=0, 2, 3, 4, 5, 8) alloys undergo one-step transformation from cubic L21→monoclinic 7M modulated structure as cooling. The martensitic transformation temperatures firstly increase then decrease with the increase of Co content, and increase with the increase of Fe content. This is because the doping changes the matrix composition. At this time, there is not only (102)M I-type twin but also (111)M I-type twin relationship between variants in these 7M martensite.The compressive experiment indicated that the fracture stress and fracture strain of Ni50Mn50-xInxalloys increase slightly with the decrease of In content, but increase significantly after doping Co and Fe element. When the Co content is 8at.%, the fracture stress and fracture strain are as high as 1420MPa and 20.5%. The main reason of the plastic increase by doping Co and Fe is that the fccγphase particles delay the crack of grain boundaries, and the fraction type changes from intergranular crack to transgranular crack as the Co or Fe content increase. This also indicates that the ductility of the alloys is improved significantly.The magnetic measurement illustrates that the Curie temperature has no obvious changes with the change of In content. As the In content is no less than 15at.%, the Curie temperature of the alloy is higher than martensitic transformation temperature, and transform from paramagnetic martensite to ferromagnetic parent phase. As the In content is less than 15at.%, the Curie temperature is lower than martensitic transformation temperature, and then magnetic field induced phase transformation can not be observed at this time. The Curie transformation temperatures increase after the addition of Co and Fe replacing In partially, the Curie temperatures of Ni50Mn34In8Co8 and Ni50Mn34In14Fe2 alloys are higher than the martensitic transformation temperatures, and could observe the magnetic field induced phase transformation behaviour. In addition, Ni50Mn34In14Fe2 alloy has large magnetocaloric effect, and the magnetic entropy change is as large as 53J/kgK with a magnetic field of 8T.
Keywords/Search Tags:magnetic shape memory alloy, Ni-Mn-In alloy, martensitic transformation, microstructure, magnetic properties
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