High angle boundaries and orientation distributions at large strains

Abstract

The boundaries in heavily cold worked metals originate not only from grain boundaries present in the undeformed metal, but also from dislocation boundaries which form during plastic deformation at places where the grains subdivide. At large strains this subdivision occurs on a very fine scale much less than one micrometer, making it difficult to obtain quantitative microstructural and crystallographic information. Qualitatively it is known that these boundaries have a large angular spread and that the misorientation across many boundaries is of a magnitude characteristic of ordinary high angle boundaries (i.e. larger than 15--20 {degree}). This study will quantitatively analyze this angular spread in heavily cold worked nickel and discuss the effect of this spread on the macroscopic crystallographic texture following deformation. A significant number of high angle boundaries are crated during deformation which are far in excess of the number of original grain boundaries. Thus, single grains subdivide into different texture components separated by sharp boundaries during deformation. Since these high angle boundaries make sharp transitions between texture components, they are not deformation or transition bands. The local orientation differences measured between crystallites and the average macroscopic texture provide important quantitative smoothing or scattering factors for crystallographic texture predictions.