Disorientation-based classification of mesostructures in severely deformed copper alloys

Long-range interactions and correlations are distinctive attributes of non-equilibrium processes. A suitable tool for studying long-range interactions in polycrystalline materials is the orientation correlation function. It was introduced as early as 1965 using the concept of mesotexture which incorporates information about grain orientations and geometries. However, its application has been limited because most materials’ characterisation works are still focused on conventional texture analysis. More recent studies proved that grain-grain interactions were independent of grain size, but did not go further to consider the longer-range interactions on structure development. The present study uses a novel discrete methodology for reconstruction and analysis of polycrystalline structures obtained by EBSD microscopy that allows for the first time to reveal and quantify the long-range effects on structure evolution of severely deformed Cu-0.1%Cr-0.1%Zr, Cu-0.1%Cr-0.1%Zr-0.05%Y, Cu-0.3%Cr-0.5%Zr and Cu-0.25%Mg (wt%) alloys. It is shown that the first- and second-order grain neighbours in all considered alloys obey scale-invariant power-law dependence as revealed in the previous studies with the first-order grain neighbours. However, our results show that the scale invariance extends much farther, between the fourth and seventh grain neighbours, depending on the material and accumulated plastic strain. These results cannot be explained by the conventional size effect reasoning discussed in previous publications. They suggest that the material discreteness, in the sense of numbers rather than sizes of grains, is the origin of the observed long-range correlations and the emergence of mesostructure that breaks the scale invariance. • New mesostructure intensity measure detects and classifies micro-shear bands. • Computationally effective discrete method proposed for mesostructure analysis. • Scale invariance in studied materials extends up to 8 orders of grain neighbours. • Combinatorics (grain numbers) governs long-range orientation correlations.