Further evidence of grain boundary internal friction in bicrystals

In order to further confirm the origin of grain boundary (GB) internal friction peak in bicrystals, the effect of GB density (i.e., GB area in unit volume of specimen) on the internal friction peak in pure aluminum is studied. It is found that the increment of GB density leads to a proportional increment of the peak height (or relaxation strength), while the activation parameters remain unchanged. The results further confirm that the observed internal friction peak in bicrystals is induced by the GB, rather than lattice dislocations in grain interior. By analyzing the stress components acting on the GB plane in bicrystals, the internal friction peak is interpreted by stress induced GB sliding. The restoring force to sliding is assumed due to the faceted junctions or steps in GBs.