| 题名 | 整体抗氧化超高温复合材料研究 |
| 作者 | 谢昌明 |
| 学位类别 | 硕士 |
| 答辩日期 | 2012-06-02 |
| 授予单位 | 中国科学院研究生院 |
| 导师 | 张伟刚 |
| 关键词 | C/C-ZrB2-ZrC-SiC 力学性能 热物理性能 抗氧化性能 抗烧蚀性能 |
| 其他题名 | Study on the Ultra-high Temperature Oxidation Resistant Composites |
| 学位专业 | 化学工程 |
| 中文摘要 | 发展高超声速飞行器及超燃冲压发动机迫切需要超高温抗氧化复合材料。复合材料不但能够承受特别高的温度环境(～2500℃)，还要具有优良抗氧化、抗烧蚀性能和优良力学性能。本论文以炭纤维为增强增韧相，以超高温陶瓷为耐超高温烧蚀基体，采用新近研制成功的ZrC、ZrB2陶瓷前驱体，制备了新型炭纤维增强纳米复相陶瓷基复合材料。研究了前驱体裂解过程、材料致密化过程、组成成分、微结构、力学性能、热物理性能、抗氧化和抗烧蚀性能，探讨了其抗氧化和抗烧蚀机理。主要内容和成果如下： (1) 研究了ZrC、ZrB2陶瓷前驱体的热解过程，发现经1500℃热处理后，分别完全转化为ZrC、ZrB2陶瓷，颗粒尺寸均为纳米级。采用化学气相沉积工艺制备密度为0.51g/cm3、0.68g/cm3和0.88g/cm3的三种C/C(A、B和C)，以ZrB2前驱体、ZrC前驱体和聚碳硅烷配制的复合陶瓷前驱体为浸渍剂，通过聚合物浸渍裂解工艺制备A、B和C三组C/C-ZrB2-ZrC-SiC复合材料。浸渍初期，材料密度随浸渍次数的增加而呈线性增长；随着循环次数继续增加，密度增大幅度逐渐变缓。A、B组材料的致密化趋势相似，C组密度增速小于前两者。分析认为，随着热解炭含量增加，为浸渍基体留下的空间减小，使密度增速减小。B组材料密度最大，达2.06 g/cm3。 (2) 研究了复合材料的多尺度结构。发现炭纤维由一层热解炭所包裹，热解炭外围为连续致密的纳米复相陶瓷基体，该基体是由ZrB2和ZrC纳米颗粒均匀地弥散于SiC连续相而形成，可大幅提高材料的抗热震性能、高温抗氧化和抗烧蚀性能。炭纤维、热解炭和复相陶瓷基体紧密结合而构成了C/C-ZrB2-ZrC-SiC复合材料整体。 (3) 发现复合材料的弯曲强度和断裂韧性均随热解炭含量增加而呈现先上升后下降的变化趋势。试样B表现出最高的弯曲强度和断裂韧性，分别达127.9MPa和6.23MPa·m1/2。研究其断裂失效形式和断口形貌，发现材料载荷-位移曲线达到最大载荷后呈现台阶式的缓慢下降趋势，材料失效形式为韧性断裂，具有假塑性断裂特性。材料断口呈锯齿状，断口处纤维拔出多而长，且被拔出的纤维形貌完整。表明在制备过程中炭纤维与基体形成弱的界面结合，能使材料在承受载荷发生弯曲变形时发生脱粘和纤维拔出，大幅提高材料断裂韧性。 (4) 复合材料的比热容与热导率均随温度升高而增大，但增大的趋势逐渐减弱。炭纤维及环绕纤维生长的热解炭是热传导的有效通道，因此沿纤维轴向的热导率高。材料的热膨胀系数(CTE)在低温段随着温度的升高缓慢增大。这是由于在测试过程中，纤维/基体界面在材料制备冷却过程中产生的残余热应力逐渐释放，陶瓷基体是主要控制因素。在高温段，CTE的变化主要取决于纵向炭纤维的轴向热膨胀和界面的热应力。通过A、B和C组试样之间对比，随着热解炭含量升高，复相陶瓷基体含量降低，材料CTE逐渐减小，这是由于炭纤维和热解炭的CTE远小于复相陶瓷基体。 (5) 研究了复合材料的氧化行为。发现随着氧化温度的升高，复合材料失重率逐渐增大，弯曲强度保留率逐渐下降，在1300℃氧化60min后试样弯曲强度保留率为52.5%。在900℃氧化后，材料表面热解炭和炭纤维被氧化，部分基体氧化生成ZrO2、玻璃态SiO2和B2O3；随着温度升高，表面生成的ZrO2含量增多，并伴有玻璃态ZrSiO4的生成，由于B2O3蒸气压增大而加速其挥发，气体产物的逸出形成了大量气孔，加剧氧向材料内部扩散，使炭纤维被氧化而降低材料弯曲强度。通过化学气相沉积工艺在材料表面制备一层SiC涂层，能封填材料固有孔隙，有效阻止氧向材料内部渗入，在中低温氧化环境对材料起到显著抗氧化作用。 (6) 采用等离子体烧蚀试验考察了复合材料的抗烧蚀性能。发现随着烧蚀温度升高，材料线烧蚀率逐渐增大。在2200℃烧蚀时，线烧蚀率和质量烧蚀率分别为1.67×10-3mm/s和1.66×10-3g/s。与C/C-SiC复合材料进行对比试验，C/C-ZrB2-ZrC-SiC复合材料在2200℃时的线烧蚀率和质量烧蚀率分别降低了85.8% 和71.0%，表现出优异的超高温抗烧蚀性能。分析原因，在烧蚀过程中，材料表面快速生成了以ZrO2为骨架，ZrO2-SiO2玻璃相弥合其中的粘稠玻璃态覆盖层，有效阻止氧向材料内部扩散，从而保护材料基体。通过电弧风洞烧蚀试验进一步验证了材料优异的抗烧蚀和抗热震性能。 |
| 英文摘要 | Development of hypersonic vehicles and scramjet is in great need of ultra-high temperature and oxidation resistance composites. The composites should bear extra high temperature (~2500 °C) and present excellent mechanical properties, oxidation and ablation resistance. In this study, carbon fiber is used as a toughening and strengthening phase, ultra-high temperature ceramics is used as ablation resistance phase, carbon fiber-reinforced nanosized dispersed ceramic matrix composites were prepared with ZrC and ZrB2 polymeric precursors synthesized by our laboratory. Pyrolysis process of precursors, fabrication, composition, microstructure, mechanical properties, thermal properties, oxidation and ablation resistance of composites were investigated. Also the anti-oxidation and anti-ablation mechanisms were discussed. The obtained main results are summarized as follows: (1) Pyrolysis process of ZrC and ZrB2 polymeric precursors was investigated. It was found that precursors had been completely transformed into ZrC and ZrB2 particles with the sizes of nanometer during heat treatment at 1500 °C, respectively. The C/C composites with density of 0.51 g/cm3, 0.68 g/cm3, and 0.88 g/cm3 (A, B, and C) were prepared by chemical vapor infiltration. The C/C-ZrB2-ZrC-SiC composites named A, B, and C were prepared by polymeric impregnation and pyrolysis with composite precursors obtained by polycarbosilane, ZrC, and ZrB2 polymeric precursors. The density shows a linear increase with the number of PIP cycles at first, it then turns a gradual decrease in the impregnation efficiency after several cycles. The trend of A looks like that of B, but the impregnation efficiency of C is the least among the three. The left room for matrix in PIP decreases with increasing of the content of pyrolytic carbon (PyC), making a decrease in increasing rate of density. The density of B is the biggest, reaching at 2.06 g/cm3. (2) The multiscale structure of composites was investigated. It was found that carbon fibers are covered by PyC. The continuous complex ceramic matrix is well distributed, formed by ZrB2 and ZrC nano-particles distributing homogeneously in the continuous SiC phase, beneficial to the thermal shock resistance, high-temperature oxidation and ablation resistance of composites. The PyC is integrated with carbon fibers and ZrB2-ZrC-SiC matrix, forming the C/C-ZrB2-ZrC-SiC composites. (3) The flexural strength and fracture toughness of composites increase at first and then decrease with increasing of PyC. Sample B presents the highest flexural strength (127.9 MPa) and the highest fracture toughness (6.23 MPa·m1/2). The fracture behaviors and fracture morphology were investigated. The curves of load versus displacement decrease gradually after reaching the maximum fracture force. The composites exhibit a pseudoplastic failure behavior. The fibers show pullout in the fiber bundle. The interfacial debonding and sliding of PyC interphase occur between fiber and matrix, leading to higher fracture toughness. (4) The specific heat capacity and thermal conductivity both tend to go up with temperature. The increasing rates decrease gradually. Carbon fibers and PyC are the major paths of heat conduction, so thermal conductivity increases along the orientation of the carbon fiber. Coefficient of thermal expansion (CTE) of composites increases gradually at low temperature, due to the release of residual thermal stress produced at fiber/matrix interface in the preparation. Ceramic matrix is the main controlling factor. Changes in the CTE at high temperature depends on axial thermal expansion of longitudinal carbon fiber and thermal stress of the interface. Among A, B, and C, the CTE of composites decreases with increasing of PyC and decrease of complex matrix, due to the CTE of carbon fiber and PyC less than that of ceramic matrix. (5) The oxidation behavior of composites was investigated. The mass loss rate increases when strength retention decreases gradually with oxidation temperature. The strength retention of composites is 52.5% after oxidation at 1300 °C for 60 minutes. At 900 °C, PyC and carbon fiber in the surface were oxidized when ZrO2, SiO2, and B2O3 were produced by oxidation of matrix. The content of ZrO2 increases and the glass ZrSiO4 was produced with oxidation temperature. The increasing vapor pressure of B2O3 accelerated its volatile. A great deal of pores formed due to the escape of gaseous products, speeding up the oxygen diffusion into composites and reducing flexural strength by oxidation of carbon fibers. It is effective that adding SiC coating at surface of composites to seal the pores, to prevent the spread of oxygen, to protect the composites from oxidation at low and intermediate temperature. (6) The ablation behavior of composites was investigated by plasma torch heating technique. Linear ablation rate increases with temperature. The linear and mass ablation rates are 1.67×10-3 mm/s and 1.66×10-3 g/s at 2200 °C, respectively. In comparison with C/C-SiC, the linear and mass ablation rates for C/C-ZrB2-ZrC-SiC composites decrease by 85.8% and 71.0%, respectively. The C/C-ZrB2-ZrC-SiC composites exhibit good ablation-resistive endurance, due to viscous glass scale with ZrO2 as a skeleton and SiO2 wetting the skeleton preventing the spread of oxygen and protecting the matrix from further oxidation. The good ablation and thermal shock resistance were verified by arc-heated wind tunnel. |
| 语种 | 中文 |
| 公开日期 | 2013-09-25 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1798]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 谢昌明. 整体抗氧化超高温复合材料研究[D]. 中国科学院研究生院. 2012. |
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