The high density β-sialon was fabricated under the presence of SiO vapor. The increase in the amount of excess Al2O3 over “balanced” sialon composition increased the density of sintered sialon and the amount of intergranular X-phase.
The bending strength of reaction sintered β-sialon was measured from room temperature to 1400°C. The strength of z=2 sialon with 1.2wt% excess Al2O3 in starting composition (β2-1) was 40kg/mm2 in average and 45kg/mm2 in maximum at room temperature. The strength degradation was not observed up to 1200°C. The strength of z=2 sialon with 2.4wt% excess Al2O3 (β2-2) was 43kg/mm2 at room temperature. The strength of β2-2 was lower than that of β2-1 at high temperatures due to larger degree of strength degradation.
The strength of β-sialons with z=1.5 and 3 was also measured. The strength of z=1.5 sialon (β1.5) was lower than that of β2-1, but the degree of strength degradation was smaller at high temperatures. The strength of z=3 sialon (β3) at room temperature was between that of β2-1 and β1.5. The strength of β3 at high temperatures was lowered by the presence of un-dissolved material at grain boundaries in sintered sialon.
The microstructural study revealed that the strength degradation at high temperatures was related to the intergranular fracture based on grain boundary sliding mechanism.
The origins of fracture initiation detected in present work were large pores, large particles and surface flaws.