A novel porous carbon synthesized to serve in the preparation of highly dense and high-strength SiC/SiC by reactive melt infiltration

Abstract

SiC/SiC composites, prepared by reactive melt infiltration (RMI), exhibit exceptional properties. However, the presence of residual Si in the composite matrix can significantly compromise their high-temperature mechanical properties. Addressing the issue of high-content residual Si aggregation remains a crucial focus of research in order to fully unlock the application potential of SiC/SiC composites prepared by RMI. In this work, a special porous carbon (Cg) is successfully synthesized and introduced into the porous 2D SiC/SiC composites prepared by CVI. The unique pore structure of the SiC/SiC-Cg is thoroughly analyzed, along with its liquid Si infiltration process. The difference in coefficient of thermal expansion (CTE) between SiC and Cg can cause thermal stress, which can destory the Cg structure. Consequently, the C particles detach from the Cg skeleton and react with liquid Si to create SiC. This process effectively separates residual Si and helps alleviate the negative effects of residual Si aggregation. The microstructure and phase distribution of SiC/SiC composites obtained by liquid Si infiltrating different C structures are investigated and compared, and it demonstrates the positive effect of Cg on the uniform phase distribution of matrix in the composites. The as-received SiC/SiC composites possess a density of 2.94 g/cm3 with open porosity of 1.23 %, and a flexural strength of 808.7 ± 10.2 MPa, a fracture toughness of 25.5 ± 1.8 MPa·m1/2, a tensile strength of 317.4 ± 12.4 MPa and a proportional ultimate stress of 157.33 ± 4.1 MPa. Acoustic emission (AE) and digital image correlation (DIC) technology are used to study the special mechanical behavior of composites.