添加碳化钽炭/炭复合材料的制备及其性能研究

【作者】 赵磊；

【导师】 张红波；

【作者基本信息】 中南大学 ， 材料学， 2007， 硕士

【摘要】 炭／炭复合材料具有质轻、抗热震、耐高温、耐烧蚀和粒子侵蚀、高温强度高、膨胀系数低等优异性能，是一种理想的喷管材料，广泛应用于固体火箭发动机。新一代高性能固体火箭发动机的出现，对发动机喷管喉衬的抗烧蚀性能提出了更高的要求。本文以炭纤维针刺整体毡为预制体，采用在预制体成型过程中添加碳化钽粉末的新方法，经过化学气相沉积和树脂浸渍／炭化混合增密，制备添加碳化钽炭／炭复合材料。考察了碳化钽含量、热处理温度和热解炭含量对材料的组织结构、导热系数、力学性能、氧化烧蚀性能的影响，通过对材料进行光学显微镜、扫描电镜和X射线衍射等分析，探讨了材料性能的影响因素及影响机理。研究结果表明：(1)与未添加碳化钽的复合材料相比，在制备工艺条件相同的情况下，添加碳化钽能提高炭／炭复合材料的石墨化度，表明碳化钽具有一定的促进石墨化作用。(2)在相同的热处理温度下，随着碳化钽含量的增加，材料的石墨化度提高，微晶尺寸增大，层面间距减小，材料垂直方向的导热系数降低，而平行方向的导热系数却由于碳化钽促进石墨化作用而先增大后减小。(3)对于剪切破坏模式，未添加碳化钽炭／炭复合材料表现为假塑性断裂方式，断裂功较高，而添加碳化钽炭／炭复合材料为脆性断裂方式，断裂功较小。对于压缩破坏模式，添加碳化钽的炭／炭复合材料与未添加碳化钽的炭／炭复合材料相似。材料的平行压缩载荷-位移曲线均呈抛物形特征，失效机制既有层间分层、又有剪切断裂。垂直压缩表现为对角的剪切破坏或层问分层或二者结合的复合失效模式。(4)在相同氧化条件下，添加碳化钽炭／炭复合材料的氧化失重率较未添加碳化钽的试样略有减少，且材料的氧化起始温度随碳化钽含量的增加而提高，表明碳化钽的添加可在一定程度上改善材料的抗氧化性能。(5)碳化钽颗粒的添加使材料的力学性能降低，同时烧蚀过程中生成液态氧化钽，加大了机械剥蚀和熔化流失等力学因素引起的质量损失，同时液态氧化钽的流失使表面粗糙度增大，恶化了烧蚀条件，综合作用的结果是加大了复合材料的烧蚀率。(6)添加碳化钽炭／炭复合材料的氧-乙炔烧蚀机制呈热化学烧蚀、热物理烧蚀和机械剥蚀的综合作用。在试样的中心区以热物理烧蚀和机械剥蚀为主；在烧蚀过渡区和边缘区以热化学烧蚀为主。更多还原

【Abstract】 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.更多还原