Mechanical properties of porous Si3N4–SiC composites fabricated at 1200 °C

Abstract

Porous Si3N4–SiC composites are potentially very attractive for various advanced applications such as aerospace and solar thermal power plants. However, processing of these porous composites is difficult and expensive due to the requirement of very high temperatures. In the present work, porous Si3N4–SiC composites were fabricated at only 1200 °C using phosphoric acid both as a pore former and binder. Porous composites with a constant SiC content were fabricated using various H3PO4 content and the morphology and mechanical properties of the porous composites were systematically investigated. The addition of SiC particles resulted in significant improvement of stiffness, compressive strength, and flexural strength over monolithic porous Si3N4, and porous composites fabricated using 40 vol% H3PO4 yielded the best properties of longitudinal elastic constant >50 GPa, flexural strength >80 MPa, and compressive strength >180 MPa. The achieved mechanical properties have been discussed in light of the analytical micromechanical models for Young's modulus and minimum solid area theory. Finally, the influence of processing temperature on the evolution of porosity and crystalline phases has been systematically studied and the dependence of porous composites' stiffness on these parameters has been investigated in detail.