High-purity SiAlON materials of the form, Si6-xAlxOxN8 (where x was 1, 2 or 3), were characterized with regard to the structure and viscosity of internal grain boundaries. Internal friction experiments provided a direct measure of the intrinsic viscosity of grain boundaries, and incidentally revealed the occurrence of a grain-boundary interlocking mechanism that suppressed sliding. A residual glass phase (consisting of Al-rich SiO2) and nm-sized mullite residues were found at glassy triple grain-junctions of the x = 1 SiAlON. A low melting-point intergranular phase dominated the high-temperature behavior, and caused grain-boundary sliding at temperatures as low as 1100C. In these materials, relaxation which resulted from grain-boundary sliding was suppressed and the internal-friction curve exhibited an exponential-like increase.

Structure and Viscosity of Grain Boundary in High-Purity SiAlON Ceramics. G.Pezzotti, H.J.Kleebe, K.Okamoto, K.Ota: Journal of the American Ceramic Society, 2000, 83[10], 2549-55