In-situ whiskers reinforced silicon nitride matrix composites

Two new methods for preparing in-situ whiskers reinforced silicon nitride matrix composites are proposed. Direct nitration of CaF₂ addition silicon compact or infiltration treatment of reaction sintered pre-nitride porous Si₃N₄ compact in phenolic resin and tetraetyl silicate using La₂O₃ as catalyst followed by high temperature heat-treatment, in-situ β-Si₃N₄ or β-SiC whiskers will grow out respectively in the matrix. Droplet on top of each β-SiC whisker was observed, which suggests that whisker grows through vapour-liquid-solid mechanism. When two or more such whiskers with different directions occur, the whisker network is formed. The microstructure of in-situ whisker depends on the experimental conditions. With the increase of time and temperature. The in-situ whisker becomes wider and longer. The experimental results show that in-situ whiskers can increase not only the fracture strength but also the fracture toughness.