Experimental and theoretical investigation on the effect of crack dimension on the crack-healing performance of Si₃N₄/SiC_w composite ceramic

Si₃N₄/SiC_w composite ceramic was selected for researching the crack-healing performance. Pre-cracks with different lengths were introduced on the tensile side of specimens by Vickers hardness tester. Subsequent to heat treatment at 1300 °C, it is able to completely heal a crack of 200 μm, thereby achieving a substantial strength recovery for pre-cracked specimens even with much longer cracks (1200 μm) after heat treatment at the optimal heating temperature of 1300 °C. Crack closure and strength recovery of the pre-cracked specimen is considered to be triggered by the creation of SiO₂, liquid aluminosilicate and silicon yttrium oxide by the oxidation reaction as filling mechanism during heat treatment. There is a theoretical model proposed to demonstrate the strength recovery rate of pre-cracked specimens, and to predict that the strength ratio of pre-cracked specimens with different initial crack length after and before heat treatment at the same healing condition should be of the similar value, which it is confirmed by experimental results.