【作者】 李斌；

【导师】 张长瑞；

【作者基本信息】 国防科学技术大学 ， 材料科学与工程， 2007， 博士

【摘要】 天线罩是高超音速导弹的关键部件之一,必须具备防热、透波、承载等多种功能,以满足导弹制导系统正常工作的需要。本文在全面综述国内外航天透波材料和烧蚀材料研究进展的基础上,以研制功能分离式高超音速导弹天线罩为目标,针对不同功能区对材料性能的不同要求,对各功能区的材料体系进行了设计,合成了新型的氮化物陶瓷先驱体混杂聚硼硅氮烷（H-PBSZ）,通过先驱体浸渍—裂解（PIP）工艺制备了碳纤维增强氮化物（CFRN）耐烧蚀复合材料和石英纤维增强氮化物（SFRN）透波复合材料,并对烧蚀材料表面涂层的制备进行了初步探索。在此基础上,实现了不同功能区材料的整体成型,并制备出了全尺寸的整体天线罩构件。合成了新型氮化物陶瓷先驱体H-PBSZ,并对其交联和裂解过程进行了研究。分别合成硼吖嗪和全氢聚硅氮烷,使二者在一定条件下聚合,得到H-PBSZ。H-PBSZ结构中含有N-H、B-H、Si-H、B-N以及Si-N等化学键,在低温密闭环境中保持稳定。H-PBSZ在受热时会实现交联固化,交联过程中增大反应室气压可减小所放出的气泡的体积,并减缓其上升的速度,使交联反应平稳进行;同时可抑制放气反应的进行,减少气体的放出量,从而有效地抑制先驱体的“发泡”现象。H-PBSZ的交联产物可在氨气中发生高温裂解,随着裂解温度的升高,裂解产物的结晶度和稳定性均随之提高,1600℃实现完全陶瓷化,陶瓷产率约83wt%。H-PBSZ的最终裂解产物为BN和Si₃N₄的混合物。H-PBSZ是一种合适的PIP陶瓷先驱体。首次以H-PBSZ为先驱体,通过PIP工艺制备了3D CFRN复合材料。在PIP工艺循环过程中,随着循环次数的增加,复合材料的密度逐渐增大,孔隙率逐渐减少,4个PIP循环后复合材料基本达到致密;力学性能逐渐提高,弯曲强度和弹性模量均逐渐增大;烧蚀性能明显改善。在交联过程中,随着交联气压的升高,先驱体的“发泡”现象得到有效抑制,复合材料的密度及综合性能得以提高。交联气压为8MPa时,3D CFRN复合材料的密度达1.65g/cm³。当裂解温度从800升至1300℃时,3D CFRN复合材料的密度及力学性能均随之提高。裂解温度的不同对先驱体的浸渍效率及所得复合材料的致密度无明显影响。2100℃热处理后,3DCFRN复合材料基体中的Si₃N₄已经分解,纤维与基体间发生了严重的界面反应,生成了B₄C以及SiC,复合材料的力学性能严重下降。考察了3D CFRN复合材料的烧蚀性能,并对烧蚀过程中材料结构和形貌的变化进行了分析。在烧蚀的过程中,氮化物基体对碳纤维提供了有效的保护,使复合材料显示出了良好的烧蚀性能。T300和T700两种碳纤维增强的3D CFRN复合材料的烧蚀性能基本相同。在轨道模拟烧蚀试验中,氮化物基体表现出了优于碳纤维的耐烧蚀性能。烧蚀之后,3D CFRN复合材料烧蚀表面的Si₃N₄发生了分解,BN以及碳纤维发生了晶化。3D CFRN复合材料的烧蚀是一个热化学烧蚀与机械剥蚀相结合的过程。研究了碳纤维种类及纤维表面处理对3D CFRN复合材料力学性能的影响。T300和T700两种碳纤维增强的3D CFRN复合材料的力学性能显著不同。与T300相比,T700增强的复合材料强度更高,韧性更好,断口中可观察到大量的纤维拔出。二者力学性能的差别归因于不同的纤维表面状态及由此导致的纤维/基体界面结合强度的差异。400℃空气表面氧化处理和1000℃惰性气氛热处理均可去除碳纤维的表面胶,且能够使纤维保留足够的强度。纤维的表面氧化处理可提高T700增强3D CFRN复合材料的力学性能,但对T300增强3D CFRN复合材料的力学性能不利;纤维的热处理对3D CFRN复合材料的力学性能无显著影响。复合材料力学性能的改变归因于表面处理所带来的纤维/基体界面结合状态的变化。采用空气氧化处理的T700纤维增强,高压交联,800℃裂解制备的3D CFRN复合材料弯曲强度为268.4MPa,弹性模量为67.6GPa。对3D CFRN复合材料表面抗侵蚀涂层的制备进行了初步研究。选取涂层成分为SiC,制备工艺为化学气相沉积（CVD）。合成了新型的CVD SiC先驱体液态碳硅烷,其结构中不含腐蚀性元素。以液态碳硅烷为先驱体进行沉积时,无腐蚀性副产物。随着沉积温度的升高,先驱体的裂解逐渐完全,900℃可沉积得到较纯净的部分结晶的SiC;当载气的流量较低时,可沉积得到SiC涂层,载气流量过高时,沉积产物为SiC纳米粉体。3D CFRN复合材料表面的CVD SiC涂层致密、坚硬,显微硬度达2800～3200 kgf/mm²（HV）。SiC涂层的存在可有效地改善3D CFRN复合材料的烧蚀性能。采用H-PBSZ先驱体转化工艺制备了3D SFRN复合材料。高压交联工艺制备的3D SFRN复合材料与常压交联相比,综合性能显著提高,密度提高了8%,弯曲强度及弹性模量分别提高了35.5%和102.4%,氧—乙炔线烧蚀率下降了26.7%。随着裂解温度的升高,石英纤维的脆化加剧,3D SFRN复合材料的力学性能逐渐下降。高压交联、800℃裂解制备的3D SFRN复合材料的密度达1.83g/cm³,弯曲强度为148.2MPa,弹性模量为41.5GPa,氧—乙炔线烧蚀率为0.11mm/s,质量烧蚀率为1.07×10^-2g/s。不同工艺条件制备的3D SFRN复合材料的介电性能较为稳定,介电常数为3.31～3.34,损耗角正切为3.8～4.9×10^-3。以功能分离式整体天线罩的整体成型为目标,对各功能区的材料体系和制备工艺进行了优化设计。不同功能区的候选材料3D CFRN和3D SFRN复合材料的热膨胀系数相近,在制备过程中和烧蚀试验过程中,均具有良好的相容性。根据具体应用环境,确定天线罩材料的增强织物采用2.5D编织结构,可兼顾材料经、纬两向的力学性能;烧蚀—承载功能区为混杂纤维增强氮化物（2.5D HFRN）复合材料,其中经纱为碳纤维,纬纱为石英纤维,透波功能区为石英纤维增强氮化物（2.5D SFRN）复合材料。以H-PBSZ为先驱体,采用PIP工艺进行复合材料制备。2.5D HFRN复合材料的经向弯曲强度为259.1MPa,弹性模量为65.3GPa,断裂韧性10.78MPa·m^1/2,热导率和比热分别为1.20W/m·K和0.80 kJ/kg·K,氧—乙炔线烧蚀率和质量烧蚀率分别为0.058mm/s和5.52×10^-3g/s。2.5D SFRN复合材料的经向弯曲强度为142.7MPa,弹性模量为40.3 GPa,热导率和比热分别为0.80W/m·K和0.81 kJ/kg·K,氧—乙炔线烧蚀率和质量烧蚀率分别为0.107mm/s和1.06×10^-2g╱s,介电常数和损耗角正切值分别为3.34和4.0×10^-3,在7.5～18.5 GHz的频段内透波率大于70%。二者的综合性能优异,可满足高超音速导弹天线罩正常工作的要求。分析了天线罩构件的制备流程,优化了PIP工艺参数,选择了合适的机械加工时机,实现了各功能区的整体成型,制备出了外形、尺寸精确的大尺寸异型薄壁高超音速导弹天线罩构件。更多还原

【Abstract】 As one of key components of hypersonic missiles, the radome must possess multifunctions of thermal protection, electromagnetic transparence and load bearing to meet the requirements of the homing guidance systems. In this dissertation, based on the comprehensive review of aerospace wave-transparent materials and ablative materials at home and abroad, aiming at the requirements of different functional sections in the function separated hypersonic missile radome, the materials system in each functional section was designed, a new precursor for nitride ceramics, hybrid polyborosilazane （H-PBSZ） was synthesized, carbon fiber reinforced nitride matrix （CFRN） ablative composites and silica fiber reinforced nitride matrix （SFRN） wave-transparent composites were prepared by precursor infiltration and pyrolysis （PIP） process, and the preparation of the coating for ablative composites were explored primarily. Finally, integral formation of different functional sections was realized, and full sized monolithic radome was fabricated.H-PBSZ, a new precursor for nitride ceramics, was synthesized, and the curing and pyrolysis process of H-PBSZ was investigated. H-PBSZ was obtained from the copolymerization of borazine and perhydropolysilazane, which were synthesized separately. Chemical bonds of N-H, B-H, Si-H, B-N, Si-N and so on exist in the structure of H-PBSZ. H-PBSZ is stable in airtight atmosphere at low temperatures, and could be cured and solidified when heated. With the increase of atmospheric pressure in curing process, the volumn of bubbles originated from the precursor is decreased, and the floating velocity of bubbles is slowed down, the curing process can be calmly performed. Moreover, the reaction which emits gases can be restrained, and the amount of the gases is decreased. Therefore, the foaming phenomenon is effectively restrained. The cured H-PBSZ can be pyrolyzed in ammonia gas at high temperatures. With the increasing pyrolysis temperature, both the crystallinity and stability of pyrolytic product are increased. H-PBSZ is fully ceramized at 1600℃, and the ceramic yield is about 83wt%. The ultimate pyrolytic product of H-PBSZ is a mixture comprising BN and Si₃N₄. H-PBSZ is an appropriate preceramic precursor for PIP process.3D CFRN composites were prepared from H-PBSZ by PIP process for the first time. With the increase of PIP cycles, the density of the composites increases, the porosity decreases, and the composite becomes almost dense after four cycles; the mechanical properties are enhanced, including flexural strength and elastic modulus; and ablation resistance is improved. In the curing stage, with the increase of curing pressure, the foaming phenomenon is effectively restrained; the density and integrative properties of the composites are elevated. The density of 3D CFRN composite cured at 8 MPa reaches 1.65g/cm³. Both the density and mechanical properties of the composites increase as the pyrolysis temperature increases from 800 to 1300℃. The infiltration efficiency of the precursor and the relative density of the composites are hardly changed with the variation of pyrolysis temperature. When heat treated at 2100℃, Si₃N₄ in the matrix of 3D CFRN composites is decomposed, and the existence of B₄C and SiC is detected, which indicates the interfacial chemical reactions between nitride matrices and carbon fibers. The mechanical properties of heat treated composites decline severely.Ablation properties of 3D CFRN composites were characterized, and the variations of structure and morphologies of the composites during ablation were analyzed. Carbon fibers in the composites are protected effectively by nitride matrices when ablated, and the composites exhibit excellent ablation resistance. The ablation properties of 3D CFRN composites reinforced by T300 and T700 carbon fibers are almost the same. Nitride matrices display better ablation resistance than carbon fibers when the composite is ablated by the electric arc heater. Si₃N₄ on the ablated surface of 3D CFRN composite is decomposed, while BN and carbon fibers are crystallized. The ablation of 3D CFRN composites is a combinative process of thermochemical erosion and mechanical denudation.The effects of the type of carbon fibers and the fiber surface treatments on the mechanical properties of 3D CFRN composites were investigated. The mechanical properties of 3D CFRN composites reinforced by T300 and T700 carbon fibers are quite different. Lots of fiber pull-out can be observed on the fracture surface of the composite reinforce by T700 fibers, and it is stronger and tougher than that reinforced by T300 fibers. The different surface states of different carbon fibers result in different fiber/matrix combinations and different mechanical properties of the composites. The size on the surface of carbon fiber can be eliminated by both surface oxidation in air at 400℃and heat treatment in inert atmosphere at 1000℃, and the fiber can keep enough residual strength. Surface oxidation of carbon fiber can improve the mechanical properties of the composite reinforced by T700 fibers, while it is harmful to the composite reinforced by T300 fibers. The heat treatment of carbon fibers causes little improvement for the mechanical properties. The variation of the mechanical properties is attributed to the change of fiber/matrix combination derived from the surface treatments. The flexural strength and elastic modulus of 3D CFRN composite reinforced by surface oxidized T700 carbon fibers, cured by high atmospheric pressure curing process and pyrolyzed at 800℃are 268.4MPa and 67.6GPa, respectively.The preparation of erosion resistant coatings for 3D CFRN composite was investigated primarily. SiC was selected, and chemical vapor deposition （CVD） was performed to prepare the coatings. Liquid carborsilanes which could be used as the precursor for CVD SiC were synthesized. There is no corrosive element in the structure and there is no corrosive byproduct when liquid carbosilanes are used as the precursor for depositing SiC materials. With the increase of deposition temperature, liquid carbosilanes are pyrolyzed more completely, and pure SiC which is partly crystallized can be deposited at 900℃. SiC coatings are obtained when the flow rate of carrier gas is relatively low, while nanosized SiC powders are deposited when the flow rate of carrier gas is high enough. CVD SiC coating deposited on the surface of 3D CFRN composite is compact and hard, and the microhardness of the coating is about 2800～3200 kgf/mm² （HV）. The ablation resistance of 3D CFRN composite can be improved considerably with the existence of SiC coating.3D SFRN composites were prepared using H-PBSZ conversion method. Compared with normal atmospheric pressure curing process, 3D SFRN composites cured by high atmospheric pressure curing process exhibit much more better integrative properties, the density is increases by 8%, the flexural strength and elastic modulus are increased by 35.5% and 102.4%, and the oxyacetylene linear ablation rate is decreased by 26.7%. With the increase of pyrolysis temperature, the embrittlement of silica fibers becomes more serious, and the mechanical properties of 3D SFRN composites decline gradually. The density of 3D SFRN composite cured by high atmospheric pressure curing process and pyrolyzed at 800℃reaches 1.83g/cm³, the flexural strength and elastic modulus are 148.2 MPa and 41.5GPa, and the oxyacetylene linear ablation rate and mass ablation rate are 0.11mm/s and 1.07×10^-2g/s. The dielectric properties of 3D SFRN composites prepared by different processes are relatively stable, the dielectric constant is 3.31～3.34, and the loss tangent is 3.8～4.9×10^-3.Aiming at the integral formation of the function separated monolithic radome, the materials system and preparing process of each functional section were optimized. As the candidate materials for each function section, 3D CFRN and 3D SFRN composites have similar coefficient of thermal expansion, and they display good compatibility during the preparing and ablation processes. Based on the application environment, the radome materials are confirmed to be reinforced by 2.5-dimensional fabric, which can ensure the mechanical properties both in longitudinal direction and in latitudinal direction. Hybrid fiber reinforced nitride （2.5D HFRN） composites are used in ablation-load bearing section, wherein carbon fiber is longitudinal and silica fiber is latitudinal; silica fiber reinforced nitride （2.5D SFRN） composites are used in wave-transparent section. The radome materials were prepared from H-PBSZ by PIP process. The longitudinal flexural strength of 2.5D HFRN composite is 259.1 MPa, the elastic modulus is 65.3GPa, the fracture toughness is 10.78 MPa·m^1/2, thermal conductivity and specific heat are 1.20W/m·K and 0.80 kJ/kg·K, and the oxyacetylene linear ablation rate and mass ablation rate are 0.058mm/s and 5.52×10^-3g/s. The longitudinal flexural strength of 2.5D SFRN composite is 142.7MPa, the elastic modulus is 40.3GPa, thermal conductivity and specific heat are 0.80W/m·K and 0.81 kJ/kg·K, the oxyacetylene linear ablation rate and mass ablation rate are 0.107mm/s and 1.06×10^-2g/s, the dielectric constant and the loss tangent are 3.34 and 4.0×10^-3, and the wave transmittance is higher than 70% in the frequency range from 7.5 to 18.5 GHz. The properties of both composites are excellent, and they can meet the requirements of hypersonic missile radomes.The technological process for preparing full sized radome was analyzed, the parameters of PIP process were optimized, and the machining opportunity was selected. The integral formation of different functional sections was realized, and full sized, thin-walled monolithic radome which had exact shape and accurate size was fabricated.更多还原