On the Origin and Energy of Triple Junction Defects Due to the Finite Length of Grain Boundaries

Abstract. King [1] established that due to the discrete nature of their dislocation structure, finite length grain boundaries (GBs) in polycrystalline materials possess discrete values of misorientation angle. For a GB with a length that is not a multiple of the GB period, this leads to the formation of specific disclinations at their junctions with neighboring GBs, which compensate the difference between the misorientations of finite and in-finite boundaries. In the present paper the origin of these compensating disclinations within GB triple junc-tions is elucidated and their strength is calculated using the disclination-structural unit model. It is shown that for a GB with length of about 10 nm the junction disclinations can have a strength value not more than 1◦, in contrast to King’s calculations that indicate much larger values. Elastic energies of triple junctions due to com-pensating disclinations are calculated for both equilibrium and non-equilibrium structures of a finite length GB, which differ by the position of the grain boundary dislocation network with respect to the junctions. The calcu-lations show that triple junction energies are comparable to dislocation energies, and that compensating discli-nations can play a significant role in the properties of nanocrystalline metals with grain sizes less than about 10 nm