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

In order to gain insight on the influence of intergranular glass on the
fracture 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: rare-earth) oxynitride glasses. It was found
that while the interfacial debonding strength increased when an
epitaxial beta'-SiAlON layer grew on the beta-Si3N4 whiskers, the
critical angle for debonding was lowered with increasing Al and O
concentrations in the SiAlON layer. Only in the absence of a SiAlON
epitaxial layer, were debonding conditions altered by residual stresses
imposed on the interface due to thermal-mechanical mismatch. A possible
explanation for the effect of SiAlON formation and its composition on
the debonding behavior is suggested by first-principles atomic cluster
calculations. It is concluded that by tailoring the densification
additives and hence the chemistry of the intergranular glass, ii is
possible to improve the fracture resistance of silicon nitride.