Fracture toughness, strength and thermal shock behaviour of bulk plasma sprayed alumina — effects of heat treatment

Bulk plasma spraying Al2O3 produces a material with a defect rich splat-internal microstructure and a non-equilibrium phase composition which are both subject to extensive change by heat treatment. In the present work heat treatment induced changes in the strength, fracture and thermoshock characteristics of this material have been investigated and related to microstructural development. It is found that the as-sprayed intrasplat defect structure provides low energy paths for crack propagation. This results in low toughness and strength but excellent thermoshock resistance. Heat treatment increases overall porosity, but heals the defect structure and increases splat integrity, leading to a large increase in strength, accentuated R-curve behaviour and a disproportionate increase in toughness, but also a reduction in thermoshock resistance.