Abstract: The microstructure and mechanical properties of in-situ toughened Si₃N₄ were studied by principal components analysis. The microstructure can be
characterized by the first principal component of its characterization variables, which intitules complex microstructure index. Compact matrix
with fine grains and uniform large grains with great aspect ration must be ensured in order to get in-situ toughened Si₃N₄ with excellent
microstructure. It has been approved that materials with similar complex microstructure index possessing similar mechanical properties. The mechanical
properties can be characterized by the first and the second principal components of its characterization variables, which intitule mechanical
properties stability index and average mechanical properties index. The former one reflects fracture toughness and Weibull modulus which are
affected by the fluctuation of microstructure; the later one reflects the average mechanical property, namely strength.

Key words: in-situ toughened Si3N4 microstructure, characterization, mechanical property