Damage Accumulation in Hot Pressed Alumina During Flexural Creep and Anneals in Air

Damage profiles of grain-boundary cavitation which develop in hotpressed Al2O3 during flexural creep (12 and 40 MPA, 1350 C) and stress-free annealing in air (1250, 1350 and 1470 C) were generated by SEM and image analysis across internal sections of test specimens. Creep damage accumulation is driven both by the applied stress, and by internal gas pressure in the cavities. The internal pressure results from gas trapped during hot pressing, and from gas-generating chemical reactions active during testing. At machined surfaces, we find a damage-resistant skin about 15–20 pm thick below which lies a heavily cavitated region.