Mechanisms of deformation localization and mechanical twinning under the conditions of phase instability of a crystal in stress fields

A new mechanism of the deformation and reorientation of a crystal has been studied experimentally and theoretically. This mechanism, which is effective in strain localization mechanical twinning bands of metal alloys and intermetallides, is a mechanism of dynamic phase (direct plus reverse martensitic) transformations in fields of high local stresses. The features of the reorientation and the defect substructure in these bands are discussed using electron microscopy data. With models of martensitic transformations based on the concept of cooperative thermal vibrations of extended coherent objects in crystals, the atomic mechanisms of direct plus reverse transformations are analyzed and the reorientation matrices (vectors) and distortion tensors are calculated for some (fcc bcc fcc, bcc hcp bcc) variants of these transformations. The carriers and nature of the above deformation mechanism and the principal physical effects underlying this mechanism are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 28–48, August, 2004.