Abstract
A theoretical analysis of grain-boundary stability and of the equilibrium positions of dislocations in all types of observed structures has been carried out using the method of Key and Saada (1976). It is concluded that for medium angles of tilt (θ = 2° to 5°), the symmetric position, i.e. the {022} grain-boundary plane (G.B.P.), is unstable. Furthermore the {211} G.B.P. is always the position of minimum energy.
A superposition method has been developed to measure precisely the splitting separation of partial dislocations. The intrinsic-fault energy deduced from high-resolution observation, is equal to 100 erg/cm2. The extrinsic-fault energy has been estimated to be of the same order of magnitude as this or lower.
Although the core structure of dislocations is not yet completely determined, all our results are consistent with qualitative arguments on core energy based on open bonds; it explains why the sessile edge dislocation is not split.
