Preparation And Properties Of Near-Zero Expansion C/C-SiC Composites By Reaction Bonding Technique

C/C-SiC composite has great advantages in the application of space telescope and opto-mechanical structures for its merits such as lightweight, high specific strength and low coefficient of thermal expansion(CTE). Thermal expansion property is one of key parameters for opto-mechanical structures to keep excellent precision. So the fabrication of near-zero expansion C/C-SiC composite has become a focal point of Cf/Si C study. This dissertation mainly focuses on the research of following aspects: the optimization of reaction bonding technology, the sifting of carbon matrix, the optimization of C/C green-body, the effect of CVI C interface on the mechanical and thermal expansion properties, the effect of Cf content on the mechanical and thermal expansion properties. Near-zero expansion C/C-SiC composites with comprehensive properties are obtained.The key point of reaction bonding technology was optimized. The research results manifested that the best reaction bonding temperature and high thermal temperature were 1650℃ and 2000℃ respectively. Under this condition, the fabricated C/C-SiC composites ’ in-plane CTE, flexural strength and fracture toughness were-0.055×10-6·K-1, 218 MPa and 8.93MPa·m1/2, respectively.The resource of carbon matrix was sifted out from CVI C, pitch based carbon and phenolic resin based carbon. The results manifested that the best carbon matrix was pitch based carbon.The effect of CVI C interface on the mechanical and thermal expansion properties was studied. It was found that the thickness of CVI C modified interface layer has great influence on composites’ mechanical property and CTE value. The research results manifested that the best thickness of interface was 3μm. Under this condition, the composite’s in-plane CTE at room temperature, flexure strength and fracture toughness were 0.08×10-6·K-1, 242 MPa and 10.98 MPa·m1/2, respectively.The effect of Cf content on the mechanical and thermal expansion properties was studied. The research results manifested that the increase of Cf content was good for mechanical and thermal expansion properties. When the volume fraction of Cf were 25% and 30% respectively, C/C-SiC composites’ in-plane CTE at room temperature were 0.08×10-6·K-1 and-0.05×10-6·K-1 respectively. Thus, the conclusion could be made that zero expansion C/C-SiC composites could be obtained when Cf volume fraction is adjusted between 25% and 30%.