The structure of high-angle (001) CSL twist boundaries in f.c.c. metals

Abstract

The discrete lattice approach using computer simulation techniques and empirical interatomic potentials representing copper and nickel is used to calculate the structure and energy of four coincidence lattice (001) twist boundaries. These have singular misorientations of 36·9°, 22·6°, 28·1° and 16·3°, corresponding to ∊ = 5, 13, 17 and 25 respectively. It is found that for each of these boundaries three distinct symmetric structures may arise, two of which involve translations parallel to the interface. For a given ∊ and potential the energies of the three relaxed structures are found to be similar, and for each potential the energy increases with the angle of misorientation. Volume increases occurring at the boundaries are found to correspond to displacements of about 0·07 [001] for copper and 0·13 [001] for nickel and to be insensitive to ∊. Relaxations parallel to the interfaces are always compatible with the symmetry of the boundaries and tend to increase in magnitude with ∊. The implications of the results for experimental investigations of grain boundary dislocations are discussed briefly.