Asymmetric tilt boundaries in polycrystalline nickel

Abstract

A large sample population of grain-boundary geometries in annealed polycrystalline nickel has been collected and analysed. The data include all five degrees of freedom, that is, the grain misorientation plus the crystallographic orientation of the boundary plane. The most significant category of boundaries on the basis of those geometries that could give rise to `special' properties were symmetric and asymmetric tilt boundaries in the Σ = 3 system. Together, these accounted for nearly half the sampled boundaries. Certain plane combinations occurred with an above-average frequency, whereas others, e.g. the (211) symmetric tilt boundary, were not observed at all. The data were compatible with recent calculations on the energies of asymmetric tilt boundaries. Furthermore, there was some correlation between Σ = 3 boundaries and the inclination of the boundary relative to the specimen surface, which could be explained by grain-boundary area and connectivity arguments.