Debonding behavior between beta-Si3N4 whiskers and oxynitride glasses withor without an epitaxial beta-SiAlON interfacial layer

In order to gain insight on the influence of intergranular glass on the fra cture toughness of silicon nitride, the debonding behavior of the interface between the prismatic faces of beta-Si3N4 whiskers and oxynitride glasses was investigated in model systems based on various Si-(Al)-Y(Ln)-O-N (Ln: r are-earth) oxynitride glasses. It was found that while the interfacial debo nding strength increased when an epitaxial beta'-SiAlON layer grew on the b eta-Si3N4 whiskers, the critical angle for debonding was lowered with incre asing Al and O concentrations in the SiAlON layer. Only in the absence of a SiAlON epitaxial layer, were debonding conditions altered by residual stre sses imposed on the interface due to thermal-mechanical mismatch. A possibl e explanation for the effect of SiAlON formation and its composition on the debonding behavior is suggested by first-principles atomic cluster calcula tions. It is concluded that by tailoring the densification additives and he nce the chemistry of the intergranular glass, ii is possible to improve the fracture resistance of silicon nitride. (C) 1999 Acta Metallurgica Inc. Pu blished by Elsevier Science Ltd. All rights reserved.