Microstructure and mechanical properties of Si₃N₄-Fe₃Si composites prepared by gas-pressure sintering

Si₃N₄-Fe₃Si composites were prepared using Fe-Si₃N₄ as the source of Fe₃Si by gas-pressure sintering. By adding different amounts of Fe-Si₃N₄ into the starting powders, Si₃N₄-Fe₃Si composites with various Fe₃Si phase contents were obtained. The microstructure and mechanical properties of the composites were investigated. With the increase of Fe-Si₃N₄ contents, the content and particle size of Fe₃Si both increased. When more than 60 wt. % Fe-Si₃N₄ were added, the abnormal growth of Fe₃Si particles occurred and oversized Fe₃Si particles appeared, leading to non-uniform microstructures and worse mechanical properties of the composites. It has been found that Fe₃Si particles could toughen the composites through particle pull-out, interface debonding, crack deflection, and particle bridging. Uniform microstructure and improved mechanical properties (flexural strength of 354 MPa and fracture toughness of 8.4 MPa·m^1/2) can be achieved for FSN₄0.