【作者】 周长城；

【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， 2008， 博士

【摘要】 空气舵是高超音速导弹的重要部件,空气舵防热套的气动外形直接影响弹头命中精度,耐高温、抗烧蚀防热套是保证弹头再入过程空气舵气动外形的关键。本文根据高超音速导弹空气舵防热套对材料及其制备工艺要求,通过先驱体浸渍裂解工艺（PIP）低温900℃制备了C/SiC复合材料,进行了力学、热物理、氧化和烧蚀等性能考核。在此基础上,整体成型并制备出全尺寸的C/SiC复合材料防热套构件。考察了先驱体PCS的低温裂解特性。先驱体PCS裂解过程中,温度对PCS裂解转化有很大的影响,PCS在750℃发生无机化转变,产物为无定形SiC;880～1050℃裂解SiC开始结晶。随裂解温度升高,PCS裂解产物的高温稳定性增加,700℃裂解产物在后续1200℃高温处理后失重达4.02%;900℃裂解产物陶瓷化程度较高,1200℃高温处理后失重仅0.24%,高温稳定性较好。研究了制备温度对C/SiC复合材料界面、结构及力学性能的影响。随着复合材料制备温度升高,纤维.基体界面化学反应及元素扩散加重,复合材料界面结合增强,抑制了纤维—基体界面解离、纤维脱粘、纤维拔出等增韧效果的发挥,复合材料力学性能降低。700℃制备复合材料断口纤维拔出较多,复合材料呈韧性断裂,弯曲强度为256.58MPa,断裂韧性5.63MPa·m^1/2;900℃制备复合材料呈脆性断裂,弯曲强度仅54.58MPa,断裂韧性2.25MPa·m^1/2。探讨了纤维类型对复合材料的影响。与JC-1#纤维相比,JC-2#纤维表面反应活性较低,表面沟纹缺陷较少,所制备复合材料界面结合较弱,断口纤维拔出较多,力学性能较高,复合材料弯曲强度为249.84MPa,断裂韧性9.08MPa·m^1/2。开展了碳纤维热处理及其复合材料界面优化研究。热处理温度对碳纤维的结构、性能影响很大,在600～1200℃温度范围,热处理温度越高,纤维强度保留率越低,当热处理温度为1200℃时,纤维的强度保留率为79.57%。1400℃热处理有助于纤维微观结构规整化,减少纤维表面缺陷和裂纹,纤维强度保留率提高为88.17%。采用1400℃热处理碳纤维增强的复合材料界面结合适中,力学性能高,弯曲强度达58 1.04MPa,断裂韧性22.43 MPa·m^1/2。研究了PCS裂解工艺对C/SiC复合材料界面及其性能的影响。PIP工艺第一周期是复合材料界面形成的主要过程,对复合材料界面及微观结构影响很大。PCS裂解过程体积先膨胀后收缩,体积收缩易造成复合材料界面物理结合过强。采用首周期700℃裂解,后续900℃裂解工艺,制备了界面结合适中、力学性能优异的C/SiC复合材料,弯曲强度达600.28MPa,断裂韧性24.52MPa.m^1/2。确定了低温制备C/SiC复合材料的最佳工艺,并考察了复合材料的力学及热物理性能。首先,碳纤维经1400℃真空处理→上胶→编织→去胶工艺,将1400℃高温热处理引入C/SiC复合材料的低温制备,为复合材料界面改善、力学性能提高奠定基础;其次,首周期700℃裂解;最后,PIP工艺900℃裂解致密化。采用优化工艺制备的C/SiC复合材料,室温弯曲强度和拉伸强度分别为643.12MPa和299.83MPa;1600℃高温弯曲强度411.01MPa。复合材料的轴向热膨胀系数为0.180×10^-6/K（25～800℃）,径向热膨胀系数2.729×10^-6/K（25～800℃）,比热容0.98J/g·K,热导率1.26W/m·K。研究了C/SiC复合材料的氧化和烧蚀特性。复合材料氧化过程表明,基体裂纹和碳纤维裸露是复合材料氧化、性能降低的主要原因。随氧化温度升高（400～1300℃）,复合材料的质量保留率从99.76%降低到81.83%;在400～800℃温度区间,复合材料氧化后强度升高,氧化产物SiO₂玻璃体弥合基体裂纹及表面孔隙是复合材料氧化后强度升高的主要原因;当氧化温度高于800℃时,氧化温度越高,复合材料的强度保留率越低。C/SiC复合材料的氧乙炔焰烧蚀质量烧蚀率为0.0158g/s,线烧蚀率0.0279mm/s,试样表面温度2005℃。复合材料等离子体电弧烧蚀线烧蚀率为0.33mm/s,烧蚀表面热流密度约35000kW/m²,热流焓值10000kJ/kg,热流压力2.8MPa。通过平面编织、穿刺缝合实现了防热套纤维预制件的整体成型,满足防热套构件主方向（迎风面）的结构完整,保证了防热套的气动外形。采用小型火箭发动机考核了空气舵防热套1:2构件的结构安全性,结果表明,C/SiC复合材料防热套在高热流冲击下结构完整、可靠。在此基础上,优化了防热套构件成型、制备工艺,制备出全尺寸C/SiC复合材料防热套构件。更多还原

【Abstract】 As an important warhead part of new generation hypersonic missiles, aerodynamic rudder must possess thermal-insulation cover, with good ablation and high temperature resistance, to ensure the aerodynamic shape for shooting straight. In this dissertation, C/SiC composites was prepared by precursor impregnation and pyrolysis process, based on the manufacture of thermal-insulation cover for new generation missiles, and the performance, such as mechanical properties, thermal-physical properties, oxidation and ablation properties etc., was tested. Finally, integral formation of complex shaped fabric was realized, and full sized thermal-insulation cover was fabricated.The pyrolysis characteristics of precursor PCS were investigated. When pyrolyzed in inert atmosphere, PCS will transform into ceramic at 750℃, and then crystallize between 880～1050℃. With the temperature rising, the stability of pyrolyzate is enhanced. The pyrolyzate of PCS pyrolyzed at 900℃keeps stabilization at higher temperature as 1200℃, with mass residue just about 0.24%, whereas the pyrolyzate at 700℃is farther decomposed, with mass residue about 4.02%.The effect of pyrolysis temperature on the fiber-matrix interface, microstructure and properties of C/SiC composites was studied. With the pyrolysis temperature rising, the interfacial chemical reaction and element diffusion are aggravated, therefore the interfacial bonding is enhanced, restraining the interface debonding and fiber pulling out, and that degrade the mechanical properties of C/SiC composites. The flexural strength and fracture toughness of C/SiC composites prepared at 700℃is 256.58MPa and 5.63MPa·m^1/2 respectively, with lots of fiber pulling out, while the composite prepared at 900℃exhibits smooth fracture surface with flexural strength of 54.58MPa and fracture toughness 2.25MPa·m^1/2The effect of fiber type on the interface and mechanical properties of C/SiC composites was investigated. Compared with JC-1# carbon fiber, the JC-2# carbon fiber has inert surface and less surface defect, thus the C/SiC composites reinforced by JC-2# carbon fiber with moderate interface has better mechanical properties, with flexural strength 249.84MPa and fracture toughness 9.08MPa·m^1/2.The heat treatment of carbon fiber was studied. The properties of carbon fiber decrease diversely during heat treatment. As the treatment temperature reaches 1200℃, the strength residue of fiber bundles reduces to 79.59%. The 1400℃heat treatment, devoted to lessen the fiber defects and enhance the high-temperature structural stability of carbon fiber, reduces the degradation of fiber strength during heat treatment. And thus the mechanical properties of C/SiC composites reinforced by carbon fiber treated at 1400℃are improved largely, with flexural strength 581.04MPa, and fracture toughness 22.43MPa·m^1/2.The first cycle of the PIP process is the most important for that it is the critical process for interface formation, and influences the interface and microstructure of C/SiC composites remarkably. PCS will expand firstly and then shrink during pyrolysis, and the bulk shrinking will lead to stronger interfacial bonding. After the optimization of PCS pyrolysis process, the high-performance C/SiC composites, pyrolyzed at 700℃in the first cycle and 900℃in the others, was obtained, with flexural strength 600.28MPa and fracture toughness 24.52 MPa·m^1/2.The optimum process of C/SiC composites was determined. Firstly, the fiber is treated in vacuum at 1400℃, and then glued, weaved and unglued. Thus the 1400℃heat treatment is introduced into the process of low-temperature preparation of C/SiC composites, weakening the fiber-matrix interface bonding. Secondly, the sample is prolyzed at 700℃in the first cycle of PIP. Finally, the sample is densified at 900℃in the residual PIP cycles. The room-temperature flexural strength and tensile strength of C/SiC composites, prepared by optimum process, is 643.12MPa and 299.83MPa respectively, and 1600℃flexural strength is 411.01MPa. The axial coefficient of thermal expansion is 0.180×10^-6/K （25～800℃）, and the radial coefficient of thermal expansion 2.729×10^-6/K （25～800℃）, specific heat 0.98J/g·K, coefficient of thermal conductivity 1.26W/m·K.The oxidation and ablation resistance were researched. The results show that the main reason for oxidation of C/SiC composites is matrix cracks and exposed fibers. With the elevation of oxidation temperature （400～1300℃）, the mass residue reduces from 99.76% to 81.83%. In the course of 400～800℃, the strength residue of C/SiC composites are all elevated for the seal of matrix cracks and surface holes by SiO₂ film after oxidation. The mass loss rate and recession rate is 0.0158g/s and 0.0279mm/s respectively after oxyacetylene ablation, and the surface temperature is 2005℃. The ablative product is SiO₂ mostly, and presents two different conformation, keatite and tridymite, due to the dissimilar cooling rate. And the recession rate tested by plasma arc is 0.33mm/s, with heat flux density 35000kW/m², enthalpy 10000kJ/kg, and heat flow pressure 2.8MPa.The integral formation of complex shaped thermal-insulation cover was realized through plane weaving and stitching. After the 1:2 thermal-insulation cover was tested by rocket engine, the structure of cover keeps integrated, and safe and credible. Finally, after the optimization of preparation process, the full sized C/SiC composites thermal-insulation cover was fabricated successfully.更多还原