Dislocation Dipole Annihilation in Pure Sapphire (Al2O3)

Abstract

Dislocation dipoles are often formed during deformation of sapphire (Al2O3) undergoing basal slip by edge-trapping of 1/3<1120> dislocations. Tne dipole concentration remains constant with increasing plastic deformation because the formation of new dipoles due to increasing plastic strain is offset by dipole annihilation by diffusive processes. Dipole annihilation in sapphire occurs in five distinguishable steps:(1) the dipole width fluctuates by self-climb, forming narrower and wider segments; (2) narrow segments transform into faulted dipoles by self-climb; (3) both perfect and faulted dipoles pinch off to form prismatic loops, primarily by self-climb; (4) faulted loops and dipoles rotate into edge orientation; and (5) loops grow or annihilate by climb. The kinetics of dipole annihilation thus depends on both self-climb and climb, that is, on both pipe-diffusion and bulk-diffusion kinetics, and so quantitative analysis of these changes during annealing will give valuable information on diffusion in sapphire. The objective of this paper is to present a brief qualitative analysis of the kinetics of dislocation dipole annihilation in pure sapphire.