Effect of Crack Length on Strength Recovery of Silicon-Carbide-Whisker-Reinforced Silicon Nitride Upon Healing Treatment

A silicon carbide whisker (SiC w ) reinforced silicon nitride (Si 3 N 4 ) composite ceramic was selected to study the crack-healing performance. Pre-cracks of various length were introduced on the tensile side of specimens by Vickers hardness tester. The crack-healing performance as a function of heating temperature and crack dimension, as well as the crack-healing mechanism were investigated. The optimal heat treatment temperature for crack-healing of Si 3 N 4 /SiC w is 1200–1300 °C. The treatment allows complete healing of a crack of 200 μ m after heat treated at 1300 °C, and achievement of a substantial strength recovery for pre-cracked specimens even with much longer cracks (1200 μ m). Crack closure and strength recovery of the pre-cracked specimen were considered to be triggered by the creation of SiO 2 , liquid aluminosilicate glass and silicon yttrium oxide by the oxidation reaction as filling mechanism during heat treatment.