Research On Preparation And Representative Performance Of Three C/Si-C-N Composites With Different Interlayers

Carbon fiber reinforced ceramic matrix composites are considered as the most promising thermal structural candidate materials due to their many merits, which can meet the development of modern aerospace. However, there are some problems in the fabrication of C/SiC composites, such as long manufacturing cycle, high cost, low oxidation resistance using PyC or BN as the interlayers etc.T300 carbon fiber fabric preforms were used as the reinforcements of the composites.One precursor,which was cheap and innocuous,was selected for fabricating the ceramic matrix in this thesis. Three composites with different interlayers were prepared by isobaric thermal gradient CVI and precursor infiltration and pyrolysis (PIP). Si-C-N matrix and PyC interlayer were prepared by isobaric thermal gradient CVI using Hexamethyldisilane(HMDS) and cyclohexane as the precursors, respectively. Si-O-C and Mullite interlayers were prepared by PIP using Dimethyl silicone oil and the mixture of Aluminium sec-Butoxide(ASB) and Tetraethyl orthosilicate(TEOS) as the precursors, respectively. The composition and phase structure of matrix, the interlayers, the microstructure, the performance of bending resistance and the thermal physical performance of three composites were studied in the paper. Some conclusions were made as follows:The chemical constitutions of matrix were Si, C, N and 0 elements. Untreated matrix was amorphous, while P-SiC and SiCN could be formed after thermal treatment at 1500℃ for 1h. α-SiC β-Si₃N₄ and α-Si₃N₄ as well as β-SiC and SiCN were formed in the matrix after thermal treatment at 1800℃ for 2h.The mixture of ASB and TEOS could change into gel after kept at room temperature, which could transform to mullite at 997.46℃ in the way of exothermal reaction. Well-crystallized mullite was achieved after thermal treatment at 1200℃ for 2h, whose average grain size was about 35nm.The pores between fibers in three composites all appeared slender. The size of pores between fiber bundles and pores between fiber were about 100μm and 10μm for C/PyC/Si-C-N,respectively The interface bonding was relatively weak for C/PyC/Si-C-N, whose thickness was about 1.5μm. The interface bonding was relatively strong with a small amount of gaps between fiber and matrix for C/Mullite/Si-C-N and C/Si-O-C/Si-C-N. The thickness of Mullite interlayer was...