Plastic Deformation of Aluminum Oxide by Indentation and Abrasion

Transmission electron microscopy provided direct evidence that plastic deformation occurs during the room‐temperature indentation and abrasion of Al 2 O 3 . Examination of single‐crystal and polycrystalline specimens showed that high densities of dislocations are produced within the near‐surface regions by mechanical polishing with a fine diamond compound (0.25 μm) and that plastic deformation by both slip and mechanical twinning occurs during the placement of Vickers microhardness indentations. The occurrence of plastic deformation in this normally brittle material is considered to be a consequence of the nature and magnitude of the local stresses developed under pointed indenters and irregularly shaped abrasive particles. Preliminary results on the effect of annealing on the retained substructure are also presented. Annealing at 900°C and higher resulted in the reduction of residual stresses through the motion of dislocations and their rearrangement into lower‐energy configurations.