Study On Mechanic And High-temperature Properties Of C/SiC Ceramic Based Composites

Silicon carbide ceramic have many attractive advantages, including high strength, low density, excellent thermal shock and oxidation resistance. However, its poor toughness limits its large-scale application. Carbon fibers have good high-temperature mechanical, excellent thermal performance and good physical and chemical compatibility with silicon carbide. Therefore, continuous carbon fiber reinforced silicon carbide ceramic composites (C/SiC CMCs) are regarded as promising candidate for thermal structural and thermal protection materials. On one hand, the toughness of the composites is greatly improved by carbon fibers; on the other hand, they preserve many advantages of the SiC matrix, such as high strength and good high temperature stability. As a result, C/SiC composites have been popular in many application fields, especially under severe service environments. for example, they have been applied as rocket nozzles, aeronautic jet engines, heat shields and aircraft braking materials. Thus, studies on mechanical strength and high-temperature performance are both important for the application of C/SiC composites in all these fields.In this paper, three kinds of C/SiC composites,3D braided C/SiC,2.5D braided C/SiC and2D needle-punched C/SiC composites, were fabricated using various processes such as chemical vapor infiltration (CVI), precursor infiltration and pyrolysis (PIP) and liquid silicon infiltration (LSI) processes. The flexural performance, thermal expanding property and ablation property of the composites were investigated and discussed based on comparison and microstructure characterization.The result of the bending test showed that the2.5D braided C/SiC composites have an average flexural strength of213.8MPa. Although it might not be qualified to be applied as structural materials, it has already met the basic requirement of thermal protection materials. The fracture morphologies of all the3kinds of composites showed that carbon fibers were pullout from the SiC matrix in the form of fiber clusters, which can avoid catastrophic failure behavior of the composites and increase its strength.Tests of coefficient of thermal expansion (CTE) showed indicated that The CTE of2.5D braided and2D needle-punched C/SiC composites remained at a relatively low level (below2.5×10-6K-1) in the whole temperature range, which may be attractive for some applications that required good dimensional stability. The regularity of the way in which the CTE of the composites varied with temperature was attributed to the mismatch of CTE between the carbon fiber and SiC matrix as well as the changes of thermal stress in the composites.Ablation tests demonstrated that the mass loss after ablation of the3D braided C/SiC composites remained at a low level compared to that of samples from foreign company. Furthermore, the matrix showed good ablation resistance because of the addition of ZrB2ceramic phase.