Microstructure and mechanical properties of mullite-sialon composites

The microstructure of the mullite--X-phase composites made by reaction of beta -sialon and mullite is a mixture of needle-shaped particles (15 mu m) and fine particles (1 mu m). The amount of liquid phase in the composites decreases with increasing amount of X-phase. Neither cracks nor liquid phase are observed at the boundary between the X-phase and mullite. The flexural strength of the composites at 1300 deg C increases in proportion to the amount of beta -sialon addition, the composite with 10 vol.% beta -sialon having the same flexural strength that mullite shows at room temperature. The fracture toughness of the composites at room temperature is improved compared with that of mullite. Graphs, Photomicrographs. 4 ref.--AA