Characteristics And In Situ Characterization Of Martensitic Transformation In Mn-Fe-Cu Alloy

Martensitic transformation(MT) has been considered as one of themost important phase transition and also is the fundamental theory of manyfunctional materials，which makes MT have great theoretical and practicalvalues. The Mn-15Fe-5Cu(wt.%) alloy was chosen to study thecharacteristics of MT from both aspects of experiment and theory.In the aspect of experiment, this paper firstly used in situ atomic forcemicroscope(AFM) and high temperature metallurgical microscope toobserve the surface relief of matrix caused by the reverse MT in MnFeCualloy. The morphology of surface was analysed and the untwinning shear themain mechanism of the N-type surface relief was proposed. The change oflattice constants during the heating and cooling processes was measured bymeans of in situ X-ray diffraction (XRD) so as to analyze the characteristicof crystallography in MT. The internal friction, Young‘s modulus and heatflow associated with MT were investigated by using thermal mechanicaldynamic analyzer (DMA) and differential scanning calorimetry (DSC). Themicromechanism of internal friction in MnFeCu alloy could be explainedfrom the view of interfacial migration.In the aspect of theory, this paper applied the infinitesimal deformation(ID) approach theory to study the crystallography of FCC-FCT MT in theMnFeCu alloy and the calculated results were compared with those obtainedfrom the phenomenological theory of martensite transformation (PTMC).Their difference and relationship were discussed in this paper. A newmethod to calculate the surface indices of sample was proposed. The IDapproach theory and the Bergeon’s model were combined to calculate the surface relief angle and shear angle of MnFeCu alloy, which proved theshear mechanism of FCC-FCT MT.