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

Abstract

A silicon carbide whisker (SiCw) reinforced silicon nitride (Si3N4) 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 Si3N4/SiCw is 1200–1300 °C. The treatment allows complete healing of a crack of 200 μm after heat treated at 1300 °C, and achievement of a substantial strength recovery for pre-cracked specimens even with much longer cracks (1200 μm). Crack closure and strength recovery of the pre-cracked specimen were considered to be triggered by the creation of SiO2, liquid aluminosilicate glass and silicon yttrium oxide by the oxidation reaction as filling mechanism during heat treatment.