Evolution of High-Angle Grain Boundaries in a (001) Copper Single Crystal Subjected to Sliding Wear

A sliding wear test was conducted on a copper single crystal having (001) surface. In the vicinity of worn surface, equiaxed fine grains that were separated by high-angle boundaries were generated. On the other hand, formations of low-angle boundaries were predominant at the area distant from the worn surface. In the present study, the formation of low-angle boundaries that were perpendicular to the worn surface and evolution of the high-angle boundaries were investigated by the electron backscatter diffraction (EBSD) method. In the region where the low-angle boundaries were formed predominantly, lattice rotation occurred almost around the axis which is normal to the wear direction. However, from a detailed orientation analysis, local rotation axes were slightly different even in the same grain. The perpendicular low-angle boundaries could be introduced by a misorientation between adjoining areas that had such different rotation axes. Amount of the high-angle boundaries increased with decreasing depth from the worn surface. At the vicinity of the worn surface, many coincidence-site lattice (CSL) boundaries with various Sigma-values were recognized. On the other hand, near the low-angle boundary region, the CSL boundaries were limited to Sigma 13a and Sigma 25a. This characteristic distribution of Sigma-value could be understood from a model that the high-angle boundaries were generated by accumulated lattice rotation induced by the sliding wear.