The infiltration has the advantages of high efficiency and near net forming, making it the mainstream method for preparing diamond/SiC composite. However, no pressure was applied during the infiltration and the SiC matrix originated from the silicon-carbon reaction, resulting in a low diamond content and a large amount of residual silicon. This makes it difficult to further improve the properties of the composite, especially the thermal conductivity. Therefore, reaction bonded SiC (RB-SiC) was proposed as the matrix to reduce silicon content, and composition design was carried out to obtain high content of diamond. The results showed that in the prepared composite, the diamond content (61.14 vol%) reached the theoretical maximum of 90.43 %, and the silicon is only 4.79 vol%. Therefore, the thermal conductivity of composite can reach up to 665.47 W/mK. In addition, the influence of SiC particle size on phase composition, microstructure, and properties was analyzed.
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 (C g ) is successfully synthesized and introduced into the porous 2D SiC/SiC composites prepared by CVI. The unique pore structure of the SiC/SiC-C g is thoroughly analyzed, along with its liquid Si infiltration process. The difference in coefficient of thermal expansion (CTE) between SiC and C g can cause thermal stress, which can destory the C g structure. Consequently, the C particles detach from the C g 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 C g on the uniform phase distribution of matrix in the composites. The as-received SiC/SiC composites possess a density of 2.94 g/cm 3 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·m 1/2 , 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.
In this study, different reaction-bonded boron carbide (RBBC) composites with a free carbon addition from 0 to 15 wt% were prepared, and the effect of the carbon content on the mechanical properties was discussed. With the free carbon addition increase from 0 to 15 wt%, the residual silicon content in the RBBC composite decreased first and then increased. Meanwhile, the strength of the RBBC composite improved first and then worsened. In the RBBC composite without free carbon, the B4C grains are obviously dissolved, the grains become facet-shape, and the grain boundary becomes straight. The microstructure of the composite was tested by SEM, and the phase composition of the composite was tested by XRD. The RBBC composite with the addition of 10 wt% free carbon has the highest flexural strength (444 MPa) and elastic modulus (329 GPa). In the composite with a 10 wt% carbon addition, the phase distribution is uniform and the structure is compact.
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