Design, Preparation And Properties Of TaC Ceramic Modified C/C Composites

Abstract:Adding refractory metal carbides in C/C composites is an effective means to improve the mechanical properties and ablation properties of C/C composites. In this paper, CVI TaC-C/C, CVD TaC-C/C, CVI+CVD TaC-C/C composites had been prepared by isothermal chemical vapor infiltration/deposition process. The microstructure, mechanical properties, ablation properties of these composites had been analyzed. The influence of CVI TaC and CVD TaC on mechanical properties and ablation properties of the composites had been disscussed. In additon, CVI SiC/TaC-C/C had been prepared and heated at diffrent temperature. The influence of heat treatment temperature on microstructure and mechanical properties of CVI SiC/TaC-C/C composite has been analyzed. The study shows that:(1) CVI TaC has a multi-layer structure, and evenly distributed over the surface of the carbon fiber in tubular form, and the PyC/TaC combines with carbon fiber and matrix well. Along the thickness direction of C/C composite, the TaC content gradually decreases, while the carbon content gradually increases, also with obvious grain structure of TaC from needle-like fine grain to equiaxed fine grain.(2) After CVD TaC modification, the average flexural strength and fracture toughness of the composites do not significantly improve, and composites exhibites brittle fracture behavior. After CVI TaC modification, the average flexural strength and fracture toughness of the composites are significantly improved, with an change of fracture fracture behavior from brittleness to pseudo-ductility. After CVD TaC and CVI TaC modification, the average flexural strength and fracture toughness of C/C composites are289.1MPa and10.9MPa-m1/2respectively, which are the highest among these composites. At.1500℃,the average flexural strength and fracture toughness of CVI+CVD TaC-C/C composites will further increased by13.8%and25.7%.(3) The CVD TaC coating has obvious grain structure, and bonding well with C/C matrix. After CVD TaC modification, the short-term ablation property has greatly improved, while the long-term ablative property does not improve significantly. After CVI TaC modification, the short-term ablation property does not improve, while the long-term ablative property has significantly improved. After CVD TaC and CVI TaC modification, both short-term and long-term ablation property are obviously improved.(4) The SiC-TaC interlayers have a tubular structure before HTT; while the average flexural strength of the as-prepared composites is241.6MPa with a brittle fracture. After HTT at1400～1800℃, TaC interlayer is damaged to granular structure; As a result, the flexural strength of the composites declines slightly, also with a brittle fracture. After HTT at2000～2500℃, both SiC and TaC interlayer are damaged. The flexural strength declines sharply, with an obvious change of fracture behavior from brittleness to pseudo-ductility. Figure56, Table19, Reference90...