Deformation and diffusion in sapphire (α-Al₂O₃)

Abstract

A review is presented of the high temperature plastic deformation of sapphire (single crystal α-Al₂O₃), both undoped and doped with isovalent and aliovalent cations. The dislocation substructure in deformed samples is related to three different regions of the stress-strain curve and permits understanding of both work hardening and recovery.

The work-hardening model is based upon the interaction of small prismatic dislocation loops with glide dislocations, while recovery is accounted for by dislocation loop annihilation through diffusion processes. The importance of the magnitude of the bulk diffusion coefficient on the details of the dislocation structure is emphasized, and data from loop annealing studies in undoped sapphire are reported. Furthermore, bulk diffusion data are affected by the point defect reactions accompanying incorporation of Mg²⁺ and Ti⁴⁺ in impurity-doped samples.

Finally, the break-up of dislocation dipoles by pipe-diffusion is discussed, as is the role of dipole fluctuations on the dipole break-up process.