Preparation And Properties Of Tantalum Carbide Carbon / Carbon Composites

Carbon/carbon(C/C) composite has many excellent performances, such as light weight, thermal shock resistance, anti-high temperature, ablation particle erosion, high temperature strength, low thermal expansion coefficient. With the appearance of new generation of high-performance solid rocket engines, higher requirements on the anti-erosion property of engine nozzle throat material were demanded.In this thesis, The preforms with tantalum carbide were prepared by adding tantalum carbide powder into integrated carbon fiber needled felts. C/C composites were made of the preforms with TaC and densified by CVD(chemical vapor deposition) and following resin infiltration/carbonization. The effects of tantalum carbide content, temperature of heat treatment and Pyrocarbon content on the organizational structure, thermal conductivity, mechanical properties and erosion properties of composites were investigated. The influencing factors and mechanisms were discussed by optical microscopy, SEM and XRD analysis. The conclusions could be summaried as follows:(1)Under the same process conditions, graphite degree of carbon/carbon composites increased with the increasing content of tantalum carbide, which showed tantalum carbide had some role in the promotion of graphite.(2)Unde the same temperature of heat treatment, with the content of tantalum carbide increased, the graphite degree of material increased, and the crystallite size increased, the level spacing reduced, the vertical direction thermal conductivity decreased, and the parallel direction thermal conductivity increased first and then decreased because of the role of tantalum carbide promoting graphite.(3)The addition of TaC had side-effect on shear and compression (parallel and vertical fiber orientation) properties of C/C composites. For shear failure mode, C/C composites without TaC addition exihibited pseudo-plastic fracture and had higher fracture work. However, for those with TaC addition, the fracture was brittle with smaller fracture work. As for compression failure mode, that of C/C composites with and without TaC addition were similar. Parallel compression load-displacement curves both showed parabolic features, and failure mechanism established the stratified layers as well as shear fracture. Vertical compression performance showed shear destruction along right angle or delamination destruction or the two combination failure mode.(4)Under the same oxidation condition, the mass loss rate of C/C composites with TaC was slightly decreased than that without TaC. Simultaneously, the initial oxidation temperature was increased with the TaC content increased. The results showed that TaC could improve antioxidant properties of C/C composites in some extent.(5)TaC particles lowered the mechanical properties of C/C composition. During the erosion process, liquid tantalum oxides were formed, which increased the mass loss resulting from mechanical factors such as the mechanical erosion and melting loss. Meanwhile, the drain of liquid tantalum oxide from surface increased the surface roughness and then worsened the erosion conditions. The integrated results accelerated the erosion rate of C/C composites.(6)The erosion mechanism of C/C composite with oxygen-acetylene were the combination of thermochemical erosion, thermophysical erosion and mechanical erosion. In the center area, thermophysical erosion and thermomechanical erosion were the main reason. While in the transition zone and the marginal areas, thermochemical ablation was dominant.