Crack healing behaviour of silicon nitride ceramics: effect of sintering additives and starting powders

摘要

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{sub}3N{sub}4/ SiC composites is studied. The semicircular crack(average diameter was100μm) was introduced in the center of specimens, then specimens were heat treated at 1300°C for 1 hour in air or in vacuum. Bending strength was measured at room and elevated temperature up to 1200°C by 3-point bending test system. Bending strength ofcracked 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{sub}3N{sub}4/Y{sub}2O{sub}3,especially the bending strength recovered completely up to that of smooth specimen. Bending strength of cracked and heat treated Si{sub}3N{sub}4/SiC composites recovered completely up to that of smooth specimen and crack healed part has enough strength up to 1200°C.