Examination of the energy phase space of mixed copper grain boundaries by EBSD and the sphere-on-a-plate method

This article reports on an experimental study of the energy phase space of mixed copper grain boundaries by a combination of electron backscatter diffraction (EBSD) and the so-called sphere-on-a-plate method. Single crystal copper spheres with diameters of a few microns were sintered onto flat single crystal {1 1 1} copper plates, resulting in random initial grain boundary configurations. EBSD measurements together with an assumption about the grain boundary plane orientation were used for the determination of the five macroscopic degrees of freedom of the grain boundaries. The tilt and twist components of the grain boundaries were calculated making use of the interface plane scheme representation of grain boundaries. Upon annealing, the spheres rotated along gradients in the grain boundary energy phase space. Thus, points of the trajectories of single spheres could be recorded between the single annealing steps, allowing for tracing the path of single spheres towards and into energy minima regions. The results gathered from 13 spheres underline a strong complexity of the grain boundary energy phase space.