【作者】 王雅雷；

【导师】 熊翔；

【作者基本信息】 中南大学 ， 材料学， 2012， 博士

【摘要】 为提高炭/炭(C/C)复合材料的耐烧蚀性能,满足新一代固体火箭发动机对喷管材料的要求,本文采用化学气相沉积法(CVD)在C/C复合材料表面制备了抗烧蚀性能优异的HfC涂层、HfC多层复合涂层和Hf(Ta)C复相涂层。针对气态输送HfCl4计量难以精确控制的技术难点,设计和开发了一种新型送粉装置,实现了HfCl4粉末在低压条件下的精确输送,为CVD-HfC涂层的微观结构控制提供了技术保障。系统研究了沉积工艺参数对HfC涂层显微组织结构的影响,探索了CVD-HfC涂层结构形态形成的基本规律,实现了CVD-HfC涂层组织结构的可控形成,获得了三种具有典型结构特征的HfC涂层：具有等轴晶结构的HfC1型涂层、具有针状晶组织结构的HfC T型涂层和具有柱状晶组织结构的HfC2型涂层。以HfC涂层的沉积速率和沉积均匀性为研究对象,建立了涂层沉积过程控制因素与涂层沉积均匀性的关联性。沉积温度、C/Hf比和氢气浓度的增加均可加快涂层的沉积；在损耗效应和边界层阻碍效应的共同作用下,涂层沉积速率随沉积区间的下降逐渐降低。沉积过程受表面反应控制时,HfC涂层的沉积均匀性较好；沉积过程受扩散控制时,HfC涂层的沉积均匀性稍差。采用纳米压痕硬度仪研究了HfC涂层的力学性能,建立了涂层微观组织结构与力学性能的对应关系,探讨了微观组织结构对涂层力学性能的影响机制。孔隙导致涂层负载能力降低是HfC1型涂层力学性能较低的原因；HfC2型和HfC T型涂层较高的力学性能主要得益于致密的结构和紧密的组织排列。利用氧乙炔焰研究了HfC涂层的抗烧蚀性能,分析了涂层微观组织结构在烧蚀过程中的演变规律,探讨了HfC涂层的烧蚀过程及烧蚀控制机制,提出了HfC涂层的超高温烧蚀机理。单一结构HfC涂层中,HfC1型涂层的烧蚀稳定性最好,质量烧蚀率为-0.05mg·cm-2·s-1; HfC T型和HfC2型涂层出现了开裂和部分脱落；具有多层复合结构的HfC涂层烧蚀性能优异。HfC涂层通过隔离、消耗氧化气氛实现对C/C基体的烧蚀防护,涂层的烧蚀速率主要取决于HfC的氧化控制机制。多孔HfO2、HfCxOy和Hf02熔体的生成可使HfC氧化控制机制发生变化,随着烧蚀的进行,HfC涂层的烧蚀率逐步降低。采用化学气相共沉积法制备了Hf(Ta)C和Hf(Zr)C复相涂层,研究了复相涂层的相组成、微观结构和烧蚀性能。Hf(Ta)C复相涂层由HfC和HfTaC2组成,具有等轴晶结构特征。HfTaC2的形成有利于涂层在烧蚀过程中形成致密的氧化物层,涂层烧蚀过程中形成的高温稳定Hf6Ta2017相可提高氧化产物的抗热震性能。Hf(Zr)C复相涂层由HfC和ZrC组成,随着CH4过饱和度的降低,涂层组织结构逐渐致密,具有等轴晶结构的Hf(Zr)C复相涂层抗热震性能较好。综上所述,利用CVD法在C/C复合材料表面制备了抗烧蚀性能优异的HfC涂层、HfC多层复合结构涂层和Hf(Ta)C复相涂层,为高性能C/C喷管材料的烧蚀防护研究奠定了基础。更多还原

【Abstract】 In order to improve the ablation resistance performance of carbon/carbon (C/C) composites and meet the higher requirements for nozzle materials of the new type solid rocket motor, HfC coating, multilayerd-structure HfC coating and Hf(Ta)C coating with outstanding anti-ablation properties were successfully prepared on C/C composites by chemical vapor deposition (CVD).A novel powder carrier was designed and developed to solve the technical problem of HfCl4transport. The accurate control of HfCl4flow at low pressure condition provides technical support for the structural control of HfC coating.The influences of deposition process on the microstructure of HfC coating were investigated systematically, the basic laws of the structural formation of HfC coating are explored and the controlled formation of coating structure is achieved. HfC coatings with typical structures were prepared, the type1with equiaxed-crystal structure, the type T with needle-crystal structure and the type2with columnar-ctystal structure.Based on the deposition rates and homogeneities of HfC coating, the relatedness between homogeneity of HfC coating and the controlled mechanisms of deposition process were established. The deposition rate increases with the increased temperature, C/Hf ratio and concentration of H2. With the decline of deposition interval, the deposition rate decreases due to the effects of the loss of reactive gases and the diffusion barrier of boundary layer. HfC coating has favorable homogeneity with the deposition process controlling by surface reaction, while has lower homogeneity with the deposition process controlling by diffusion process.The mechanical properties of HfC coating were investigated by nanoindentor. The relatedness between mechanical properties and coating structure were established and the influence mechanisms of the structure on the mechanical properties were explored. The reduced capacity of load resulting from the pores is the main reason for the lower mechanical properties of HfC1coating. The increased mechanical properties of HfC T and HfC2coatings are mainly attributed to the dense crystal-arranged structures.The ablation properties were investigated by oxyacetylene torch. The structural evolution of HfC coating during ablation process was investigated. The ablation process and the controlled mechanism of HfC coating were discussed, the ablation mechanism of HfC coating at ultral high temperature was proposed. Among the HfC coatings with single structure, the HfC1coating has the favorable ablation properties with mass ablation rates of-0.05mg·cm-2·s-1, while part of the HfC T and2coatings cracks and peels during ablation. Moreover, the multilayerd HfC coating exhibits outstanding ablation resistance. The HfC coating can protect the C/C composites by sacrificial oxidation, the ablation rate of HfC coating depends on the controlled mechanism of oxidation. The oxidation mechanism changes with formation of porous HfO2, HfCxOy and molten HfO2, the ablation rate of HfC coating decreases gradually.Hf(Ta)C and Hf(Zr)C coatings were co-deposited on C/C composites by CVD. The phase composition, microstructure and ablation properties of these coatings were investigated. The Hf(Ta)C coating which formed with equiaxed-crystal structure, is composed of HfC and HfTaC2-Compared with HfC coating, the formation of HfTaC2is reasonable to the formation of dense oxide layer during ablation and the thermal shock resistance of Hf(Ta)C coating increases due to the formation of stabled Hf6Ta2O17. The Hf(Zr)C coating is composed of cubic HfC and ZrC. The density of Hf(Zr)C coating increases with the reduced concentration of CH4. The Hf(Zr)C coating with equiaxed-crystal structure has the favorable thermal shock resistance during ablation.In a word, HfC coating, multilayerd HfC coating and Hf(Ta)C coating were prepared on C/C composites with excellent anti-ablation performance, which is benefical to the further research of ablation protection for high performance C/C nozzle materials.更多还原