Directionally solidified ceramic eutectics containing alumina as a topologically continuous majority component were considered. The creep resistance of the eutectics in fibre form was based upon the tight [00▪1] texture of the alumina component, where neither basal- nor prism-planes could be activated so as to result in glide that extended the eutectic by creep in tension. Thus, creep in such eutectics was controlled by the climb of (1/3)<¯11▪1> edge dislocations out of the (11▪0) prism plane or the (1¯1▪2) pyramidal plane. In order to understand the core structure of these dislocations, a molecular dynamics simulation was made of the core structures of the (1/3)<2¯1▪0> basal edge dislocation and the (1/3)<¯11▪1> pyramidal edge dislocations on the (1¯1▪2) plane in sapphire. The simulation revealed that the equilibrium structure of the core of the pyramidal edge dislocations underwent a dissociation into 2 half-strength partial edge dislocations that were displaced vertically out of the best glide plane of cation holes with weak covalent bonding and possible fair glide resistance into 2 adjacent pyramidal planes of very strong covalent bonding. This explained the immobility, in glide, of such dislocations on the pyramidal system but no clear structural impediment was found to their climb out of the pyramidal planes.

Molecular Dynamics Simulations of Basal and Pyramidal System Edge Dislocations in Sapphire. C.T.Bodur, J.Chang, A.S.Argon: Journal of the European Ceramic Society, 2005, 25[8], 1431-9