Crack Healing and Stress Relaxation in Al₂O₃ SiC “Nanocomposites”

The crack‐healing behavior of A12O3 and Al2O3‐SiC nanocomposite was studied using Vickers indentations to generate precracks. After annealing in argon for 2 h at 1300°C, radial cracks in the nanocomposite healed: The cracks closed and there was a small degree of rebonding in the vicinity of the crack tip. In contrast, radial cracks in alumina grew when exposed to the same annealing treatment. The different responses are attributed to the fracture mode and toughening mechanism in each material: In the nanocomposite, the cracks close as the residual stresses surrounding the indentations relax. Radial cracks open and grow in A12O3 because microstructural toughening is diminished during heating to the annealing temperature. An implication is that strength‐limiting machining flaws in these materials behave similarly, thereby accounting for the strengthening effect of annealing in this “nanocomposite“ system. Copyright © 1995, Wiley Blackwell. All rights reserved