Abstract: Densified SiC_(p) reinforced Ln-Sialon(Ln-Nd and Yb) composites were fabricated to evaluate the improvement in microstructure and mechanical properties that can be achieved by α→β transformation induced by heat treatment.Nd-and Yb-Sialon/SiC_(p) composites possess quite different reactions to thermal history. Under the same conditions for heat treatment, α phaso is quitg unstablein the Nd-Sialon/SiC_(p) system and almost thoroughly transforms to β phase, with aluminum-containing melilite(M') left at pockets of grain junctions as a dominant grain boundary phase. Despite a great many elongated β grains,existing in the Nd-system, fracture toughness (K_IC) was not improved because the decrease of aspect ratio and occurrence of coalescence of grains caused by a longer heat treatment might degrade mechanical properties, especially K_IC values. Comparatively speaking, Yb₂O₃ is a kind of better densifying additive for the composites and more efficient to stabilize α structure than Nd₂O₃. As a result, Yb-Sialon/SiC_(p) composited possess higher hardness (H_v) owing to a lot of equiaxed α grins developing in the materials.

Key words: SiC, heat-treatment, Sialon, composite, mechanical properties