Dual role of deformation-induced geometrically necessary dislocations with respect to lattice plane misorientations and/or long-range internal stresses

Abstract

This work is part of a continuing effort to develop a unified picture of the role of geometrically necessary dislocations (GNDs) in the evolution of the dislocation distribution of unidirectionally and cyclically deformed crystals. In particular, the dual role of the GNDs in the development of long-range internal stresses and lattice plane misorientations which arise because of the heterogeneity of the dislocation substructure is explored. Available experimental data of cyclically and tensile-deformed copper single crystals were evaluated as quantitatively as possible in the framework of the composite model. Valuable complementary information to TEM was obtained from well-designed X-ray diffraction experiments (line broadening, broadening of rocking curves, Berg–Barrett X-ray topography). The evolution of the long-range internal stresses and of the density of the GNDs with increasing deformation could be determined quantitatively as a function of deformation for cases of both single and multiple slip. In all cases studied, the GND density was found to be small and amounted only to some per cent of the total dislocation density. From the rate of evolution of the misorientations of different types of dislocation boundaries, the latter could be classified either as so-called geometrically necessary boundaries or incidental dislocation boundaries. A number of semi-empirical relationships between the microstructural parameters on a mesoscale and the parameters of deformation that were derived in this study can provide valuable guidance in future modelling.