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Crystal Structure,Martensitic Transformation And Microstructure In Ni-Mn-In Meta-magnetic Shape Memory Alloys

Posted on:2016-02-27Degree:MasterType:Thesis
Country:ChinaCandidate:C H WangFull Text:PDF
GTID:2321330542954584Subject:Materials science
Abstract/Summary:PDF Full Text Request
In this study,martensitic transformation temperatures of Ni50Mn50-xInx(x=0,2,4,6,6.5,7,7.5,8,10,11,12,13,14)alloys were studied by differential scanning calorimetry(DSC).Then,crystal structures were determined by Rietveld method on the basis of powder X-ray diffraction(XRD)patterns.Besides,the morphological and crytsllogarphic features of the alloys were investigated by scanning electron microscope(SEM),energy dispersive spectrum analysis(EDS),transmission electron microscope(TEM),electron back scattering diffraction(EBSD).These studies were expected to provide a solid theoretical basis for the application of Ni-Mn-In alloy.Based on the analysis of DSC,the martensitic transformation temperatures are above room temperature.The martensitic transformation temperature gradually reduces with the increasing of In concentration and it is of an approximately linear relationship with the electron concentration.Band theory can explain the fundamental reason.Crystal structure was determined by means of Rietveld method on the basis of powder X-ray diffraction(XRD)patterns.The results show that non-modulated(NM)structure belongs to the face centered tetragonal(FCT)crystal system,whereas the modulated(6M)structure belongs to monoclinic crystal system.It is found that martensite structure shifts from non-modulated(NM)structure to modulated(6M)structure with the increase of In content.At room temperature,it is of a NM structure with face centered tetragonal(FCT)system when the In concentration of alloy is less than 6.When the In concentration is equal to 6.5,7,it is composed of face centered tetragonal NM and monocline 6M structure.In addition,it is found that the alloys are of a monocline 6M structure when the In concentration is larger than 7.5.Through the technique of SEM,we found that all investigated alloys are of martensite phase at room temperature.The martensite plate of NM structure is obviously wider than that of 6M structure.But there exists finer microstructure inside the plate of NM structure.It can be found from the EBSD results of Ni50Mn36In14 that in the 6M martensite plate there are four kinds of martensitic variants and three kinds of twins,that is type-?,type-?and compound twin.Twinning elements of different twinning systems are accurately determined.Results show that the shear amount of compound twin is approximately one order of smaller than that of type-? and type-? twins.The twin interfaces between different martensite variants are found to be coherent.TEM results of Ni50Mn36In14 show that it should be modulated structure,but the satellite spot is not that clear.There are two kinds of interfaces,i.e.flat interface and non-flat interface,in the Ni50Mn43In7 alloy.There are two sets of SAED in each martensite lath,this suggests that there are two kinds of variants in each of the martensitic lath and the two variants are of twin-related.
Keywords/Search Tags:Ni-Mn-In, magnetic-field-induced shape memory alloys, crystal structure, Rietveld method, martensitic transformation
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