Thermal shock properties of β-sialon ceramics

An indentation–quench method based on Vickers cracks for measuring thermal-shock properties has been applied to β-sialon materials. The thermal-shock properties have been correlated with the morphology of the β-sialon grains, the z value in the β-sialon solid solution Si6−zAlzOzN8−z and the amount of residual intergranular glass phase. z Values in the range 0.6–3.0 were tested, and the amount of residual yttrium-containing glass phase was varied between 0 and 20 vol.%. The best thermal-shock resistance was found at low z values, and was further improved by adding an intergranular glass phase. The poorest resistance to thermal shock was found for the highest z value where the presence of glass had no measurable influence. One composition (z=1.5, 10 vol.% glass) was selected for studying the influence of the microstructure on the thermal-shock properties. The microstructure was varied by applying different sintering conditions. An improvement of the thermal-shock properties and the fracture toughness was found in samples containing elongated β-sialon grains formed in situ. In general, in-situ reinforced β-sialon materials with low z values and containing an intergranular glass phase exhibited the best thermal-shock resistance and improved fracture toughness (K1c>4 MPa m12).