In the present work, the difference in crack healing behaviour of five kinds of silicon nitride with different starting powder and sintering additives, and Si
3N
4/SiC composites is studied. The semicircular crack (average diameter was 100μm) was introduced in the center of specimens, then specimens were heat treated at 1300°C for 1 hour in air or in vaccum. Bending strength was measured at room and elevated temperature up to 1200°C by 3-point bending test system. Bending strength of cracked specimen reduced to 36-59% of that of smooth specimen. However, bending strength of all monolithic silicon nitride heat treated in air at 1300°C increased since pre-crack was healed due to oxidation. In case of Si
3N
4/Y
2O
3, especially the bending strength recovered completely up to that of smooth specimen. Bending strength of cracked and heat treated Si
3N
4/SiC composites recovered completely up to that of smooth specimen and crack healed part has enough strength up to 1200°C.
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