Effect of dislocation density on the rhombohedral twinning stress of sapphire (α-Al2O3)

Abstract

The influence of dislocations on the stress to induce rhombohedral twinning has been examined in α-Al₂O₃) single crystals. Dislocation densities have been modified by basal slip induced by compression at temperatures between 1.000 and 1.300 °C, at stresses up to 400 MPa. As a consequence of this pre-deformation, sapphire is more resistant to twinning at 900 °C, the hardening corresponding to a stress increase by a factor of 10. The twin structure is strongly influenced by the dislocations which impede the motion of twin boundaries; therefore, for high dislocation density very thin twin lamellae are formed contrary to the case for low density.