Mechanisms for the Development of Martensitic Transformation of a Face-Centred Cubic Structure into a Body-Centred Tetragonal Structure

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Two mechanisms of the martensitic transformation of a face-centred cubic structure into a body-centred tetragonal structure were discussed. Some considerations concerning the characteristics of the defects at the interphase boundary were first given. According to these considerations, the transformation takes place depending upon the mechanisms of creation of perfect dislocations, which would release the strain energy caused by the transformation. Two models were proposed concerning the creation of perfect dislocations in a set of planes with regular spacing. One is a static process, in which the length of the dislocation is increased continuously by consuming the strain energy or directly the transformation energy, and the other is a dynamical process, in which the dislocation pairs are created by consuming potential energy such as stacking fault energy or strain energy stored by freezing the kinetic energies of atoms during the transformation by means of rather a complicated process. The calculated habit planes, lattice relations and deformations associated with the transformation, based on these models and on the assumption of minimum strain energy, seemed to agree with the observations ; especially, these two models could sufficiently illustrate the origins of the two different modes of transformation, Umklapp and Schiebung.
東北大学の論文