HIGH-TEMPERATURE STABILITY OF ALPHA-SIALON CERAMICS CONTAINING GLASS ADDITIONS

Typical alpha-beta and alpha-sialon starting compositions were densifi ed by hot pressing using additions of Ln(2)O(3), where Ln=Nd and Yb. T he same compositions were also prepared by pressureless sintering but containing an additional 10% and 20% of pre-prepared glass powders, of overall composition Ln(3)Si(3)Al(3)O(12)N(2). The resulting materials were hear treated at 1450 degrees C for up to 720 hours (1 month) to observe alpha --> beta sialon transformation. A combination of X-ray a nd microstructural observations showed that the high temperature stabi lity of the alpha-sialon phase differs for the two sintering additives . In Nd2O3-densified samples, the ease of alpha --> beta sialon transf ormation depends on the properties of the liquid phase. However, the e ffect of liquid phase on the stability of the alpha-sialon phase in Yb 2O3 samples is only important when beta-sialon grains are also present in the microstructure.