In order to gain insight on the influence ofintergranular glass on the fracture toughness of silicon nitride,the debonding behavior of the interface between the prismaticfaces of ?-Si3N4 whiskers and oxynitride glasses was investigatedin model systems based on various Si-(Al)-Y(Ln)-O-N (Ln:rare-earth) oxynitride glasses. It was found that while theinterfacial debonding strength increased when an epitaxial?`-SiAlON layer grew on the ?-Si3N4 whiskers, the critical anglefor debonding was lowered with increasing Al and O concentrationsin the SiAlON layer. Only in the absence of a SiAlON epitaxiallayer, were debonding conditions altered by residual stressesimposed on the interface due to thermal-mechanical mismatch. Apossible explanation for the effect of SiAlON formation and itscomposition on the debonding behavior is suggested by first-principles atomic cluster calculations. It is concluded that bytailoring the densification additives and hence the chemistry ofthe intergranular glass, it is possible to improve the fractureresistance of silicon nitride.
展开▼
