Low energy grain boundaries in silver and copper close to the melting point

Abstract

Crystallographic parameters of low energy grain boundaries in silver and copper in the temperature range 0.8-0.996 T m have been studied. The investigations have been carried out by sintering single crystalline spheres to single crystalline plates having surfaces parallel to low index planes. In the above temperature range the most important energy cusps were found to be associated with [110] tilt boundaries. This result indicates that the parallelity of close packed rows of atoms from both grains surfaces leads to low energy grain boundary structures. The distribution of misorientation angles for low energy [1 1 0] tilt boundaries is almost continuous at 0.8 T m. At higher temperatures the spheres select some orientations as more preferred than others. This set of orientations is smaller than predicted according to recent geometrical criteria for low energy boundaries. It can be interpreted in terms of grain boundary faceting in such a way that it contains compact structural units of low energy. There seems to be no connection between the type of structural units in the grain boundary and the present crystallographic criteria. This is the reason why these criteria fail to select between nonsymmetrical boundaries of higher and lower energy.