Microstructural aspects of the f.c.c.–f.c.t. transformation during deformation in γ-Mn-Cu alloy single crystals

Abstract

The thermoelastic martensitic transformation and the stress-strain behaviour associated with the transformation in manganese-rich Mn-Cu alloys have been examined by tensile testing using single crystals grown by the Bridgman method. In the case of the deformation below the martensitic transformation temperature, twinning deformation in f.c.t. martensite has preceded dislocation glide, and the strain due to twinning showed a shape-memory effect. Regarding the continuous lattice parameter change, which can be observed in the temperature region extending over 100 K below the transformation temperature, the twinning strain decreased gradually by increasing the deformation temperature. It is shown that the shape-memory strain can be estimated by assuming the configuration of the twin-related domains of the f.c.t. martensite. Just above the transformation temperature, a stress-induced transformation has been found in the tensile testing. The characteristics of the stress-induced transformation from cubic to tetragonal structure in this alloy is discussed.