Quantification of heterogeneity in microstructural refinement in metals and alloys deformed to high plastic strains

The microstructure resulting from plastic deformation of metals and alloys typically contains heterogeneity on several length scales. Here we discuss the characterization by electron backscatter diffraction of one particular aspect of such heterogeneity, namely the uniformity of refinement by high angle boundaries after application of large plastic strains. A recently developed method for the quantification of this type of heterogeneity, based on the identification of areas that remain relatively unrefined by high angle boundaries (quantified by the fraction of low misorientation regions, f_LMR), is reviewed, and an extension of this method to quantity the degree of LMR clustering is presented. Additionaly, the required choices of parameters for use of this method are discussed and some general recommendations are given. The method is illustrated by a comparison of the microstructure in samples of aluminum heavily deformed by two different processing routes, where it is shown that the f_LMR parameter provides a measure of both the efficiency and uniformity in refinement by high angle boundaries. It is also shown how this approach can be used to investigate the relationship between nucleation of recrystallization and deformation microstructure heterogeneity in samples deformed to large strains.