Fabrication and properties of in situ silicon nitride nanowires reinforced porous silicon nitride (SNNWs/SN) composites

The in situ silicon nitride nanowires reinforced porous silicon nitride (SNNWs/SN) composites were fabricated via gelcasting followed by pressureless sintering. SNNWs were well distributed in the porous silicon nitride matrix. The tip-body appearance suggested a VLS growth mechanism. The flexural strength and elastic modulus of the prepared composites can achieve 84.3 +/- 3.9 MPa and 23.3 +/- 2.0 GPa respectively (25 degrees C), while the corresponding porosity was 40.7 vol.%. Remarkably, the strength retention rate of the composites at 1400 degrees C was up to 66.1%. This is due to the excellent thermal stability of SNNWs and silicon nitride matrix. Also, the fracture toughness of the composites was improved to similar to 42% larger than pure porous silicon nitride ceramics because of the bridging effect of the NWs and the interlocking effect of beta-Si3N4 crystals. In addition, a good thermal shock resistance and dielectric properties were indicated. The good overall performance made SNNWs/SN composites promising candidate for advanced high-temperature applications.