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P-Si,N, whisker-reinforced P'SiAlON composites were fabricated by extrusion and densified, using pressureless sintering. Whisker alignment was observed in both the green and sintered microstructures. SEM analysis of polished, sintered samples showed a microstructure consisting of the original P-Si,N, whiskers in a matrix of fine SiAlON grains. SEM of plasma-etched samples and TEM analysis showed that the whiskers, as a result of grain growth, consisted of two phases, a core and a sheath layer. X-ray mapping and EDS analysis revealed that the core material contained no trace of Al, confirming the presence of original P-Si,N, whiskers. The composition of the sheath was qualitatively identical to that of the fine P'SiAlON grains in the matrix. The sheath was thus formed by the precipitation of the P'SiAION during liquid-phase sintering and led to substantial growth of the whiskers. Microdiffraction showed that the P'SiAlON grew epitaxially on the P-Si,N4 whiskers, resulting in a heavily faulted SiAlON layer.

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