Influence of pores distribution on fracture toughness of FeSi/Si3N4 composite

FeSi/Si3N4 ceramic composite was fabricated by hot pressing technique, using α-Si3N4 and Fe3Al. The toughening effect of Fe3Al on the Si3N4 matrix is explained on the basis of microstructural characterizations and schematic representations. Results indicate that the reaction between α-Si3N4 and Fe3Al results in the formation of FeSi and sialon phases at the interface. Both phases effectively restrain coalescence and movement of the gaseous reaction product, N2, retaining it in situ to form small separated pores. The dominant toughening effect of these pores reduces the interface bonding strength, consumes the crack propagation energy, and decreases the stress-concentration at the crack tip, thereby improving the fracture toughness of the matrix.