【作者】 王其坤；

【导师】 陈朝辉；

【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】 发展高超声速飞行器迫切需要零（微）烧蚀复合材料,为此必须提高现有耐超高温复合材料的抗烧蚀性能和抗氧化性能,并兼顾其力学性能,本文利用碳纤维的增强增韧机制、UHTC的耐超高温和零（微）烧蚀特性、SiC的抗氧化特性,采用PIP工艺制备了一系列2D C_f/UHTC_p/SiC复合材料。研究了PIP的工艺参数、UHTC_p种类和含量等对2D C_f/UHTC_p/SiC复合材料结构和性能的影响,同时系统地研究了复合材料的力学性能和抗烧蚀性能,探讨了复合材料的抗烧蚀机理。PIP法制备2D C_f/UHTC_p/SiC复合材料包括两个步骤:（1）材料成型过程,即预制体的制备;（2）致密化过程,即通过多次先驱体浸渍-裂解过程使预制体致密化。本文首先研究了复合材料的成型和致密化工艺,结果表明:碳布涂刷叠层工艺是制备复合材料预制体的理想方法,成型过程中,PCS/DVB配比是影响预制件完整性和UHTC_p含量的关键参数,当mPCS:mDVB=1:3时最有利于成型和提高材料中UHTC_p含量;在致密化过程中,采用单组分（PCS/xylene）真空浸渍致密化预制体,浸渍效率高,制得的材料具有结构完整、致密度高、力学性能和抗烧蚀性能好的优势。分别研究了三种UHTC_p（ZrB₂、ZrC、TaC）含量、模压压力以及热处理温度对复合材料结构和性能的影响。添加UHTC_p能明显提高材料的抗烧蚀性能,总体上,随着UHTC_p含量的提高,复合材料的抗烧蚀性能明显提高,但材料中碳纤维含量下降,力学性能随之下降。在成型时辅助压力能同时提高材料中UHTC_p和碳纤维的含量,提高材料的抗烧蚀性能和力学性能,若在交联固化时也辅以压力,则能进一步提高材料的抗烧蚀性能和力学性能。对于2D C_f/ZrB_2p/SiC而言,采用mPCS:mDVB:mZrB_2p=1:3:8.9的成型料浆,加7MPa压力进行模压-交联,1400℃处理制得的材料力学性能最优,材料中ZrB₂含量为25.5vol%,碳纤维含量为22.6vol%,SiC含量为32.5vol%,材料的弯曲强度和弯曲模量分别为252.0MPa和35.5GPa,经氧乙炔焰烧蚀考核60秒,试样表面温度达到2200℃,质量烧蚀率和线烧蚀率分别为0.0260g/s和0.0198mm/s;提高热处理温度,材料的力学性能急剧下降,但抗烧蚀性能明显提高,其中1800℃处理制得试样弯曲强度和弯曲模量分别只有27.1MPa和26.1GPa,在同样抗烧蚀考核条件下的质量烧蚀率和线烧蚀率明显降低,分别为0.0161mm/s和0.0141g/s。如何提高材料的抗烧蚀性能,同时又能兼顾材料的力学性能是应该关注的重点。对于2D C_f/ZrC_p/SiC而言,采用mPCS:mDVB:mZrC_p=1:3:23.3的料浆配比、加7MPa压力进行模压-交联、1600℃处理制得材料具有最佳结构和性能,材料中ZrC_p含量高达33.3vol%,碳纤维含量为20.3vol%,SiC含量为26.5vol%,材料的弯曲强度和弯曲模量分别为168.7MPa和31.0GPa,经氧乙炔焰烧蚀考核60秒,表面温度为2243℃,质量烧蚀率为0.0073g/s,线烧蚀率为0.0037mm/s。采用mPCS:mDVB:mTaC_p=1:3:34.0的料浆配比、加7MPa压力进行模压-交联、1600℃处理制得的2D C_f/TaC_p/SiC复合材料具有理想的结构和性能,材料中TaC_p含量为30.5含量,SiC含量为26.0含量,碳纤维含量为26.9vol%,弯曲强度和弯曲模量分别为210.9MPa和34.4GPa,质量烧蚀率为0.0193g/s,线烧蚀率为0.0142mm/s。系统研究了三种材料的常温力学性能、高温力学性能和抗氧化性能。三种2D C_f/UHTC_p/SiC复合材料的力学性能主要取决于碳纤维含量,其中2D C_f/ZrB_2p/SiC的拉伸强度为78.5MPa,2D C_f/ZrC_p/SiC的拉伸强度为67.4MPa,2D C_f/TaC_p/SiC的拉伸强度为118.9MPa;三种材料的剪切强度和断裂韧性分别均在30MPa和10MPa·m1/2左右。针对碳布叠层增强材料存在层间结合较弱,剪切强度不高的问题,论文又开展了Z向穿刺工艺对改善材料层间结合和提高材料力学性能的研究,制得2D C_f/ZrB_2p/SiC-Zpin试样的弯曲强度为247.8MPa,弯曲模量为37.8GPa,剪切强度为37.4MPa,和未穿刺试样相比,剪切强度提高20.6%,明显改善了材料构件的可加工性和材料使用时的可靠性。三种材料的抗压强度基本相当,在x、y、z三个方向测得的抗压强度均在250.0MPa左右。与2D C_f/SiC相比,2D C_f/UHTC_p/SiC具有更高的高温强度。2D C_f/ZrB_2p/SiC在1800℃时的弯曲强度为143.9MPa,强度保留率达74.1%,2000℃时的弯曲强度下降严重,仅为61.8MPa;2D C_f/ZrC_p/SiC在1800℃时的弯曲强度达165.9MPa,强度保留率为81.8%,2000℃时的弯曲强度为168.5MPa,强度保留率为83.1%,材料表现出优异的耐超高温性能;1800℃时2D C_f/TaC_p/SiC的弯曲强度是98.0MPa,2000℃时的弯曲强度为122.2MPa。在1200℃氧化环境中,由于2D C_f/ZrB_2p/SiC和2D C_f/TaC_p/SiC表面能形成B₂O3和Ta2O5自愈合结构,表现出较好的抗氧化性能,2D C_f/ZrB_2p/SiC氧化后的弯曲强度为184.3MPa,强度保留率为69.2%;2D C_f/TaC_p/SiC氧化后的弯曲强度高达197.6MPa,强度保留率为74.1%;由于ZrC氧化产物ZrO₂在此温度下为粉末状,无法形成自愈合机制,2D C_f/ZrC_p/SiC氧化后完全失去承担载荷的能力。分别研究了三种材料在两种考核环境中、不同考核工况下的抗烧蚀性能,结果表明:复合材料中UHTC_p在抗烧蚀性能上起到重要作用,三种复合材料的抗烧蚀性能均优于2D C_f/SiC。在氧乙炔考核环境中,当试样表面温度为2200℃左右时,2D C_f/ZrB_2p/SiC的质量烧蚀率和线烧蚀率为0.0062g/s和0.0052mm/s,2D C_f/ZrC_p/SiC的质量烧蚀率和线烧蚀率为0.0104g/s和0.0111mm/s,2D C_f/TaC_p/SiC的质量烧蚀率和线烧蚀率为0.0134g/s和0.0187mm/s,根据线烧蚀率由低到高的顺序为2D C_f/ZrB_2p/SiC、2D C_f/ZrC_p/SiC、2D C_f/TaC_p/SiC;当表面温度为2600℃左右时,三种试样的质量烧蚀率和线烧蚀率均明显上升,但试样表现出的抗烧蚀性能有所变化,根据线烧蚀率由低到高的顺序分别为2D C_f/ZrC_p/SiC、2D C_f/ZrB_2p/SiC、2D C_f/TaC_p/SiC;在等离子风洞中的烧蚀考核环境更加苛刻,试样的质量烧蚀率和线烧蚀率又进一步上升,此时,根据线烧蚀率由低到高的顺序分别为2D C_f/TaC_p/SiC、2D C_f/ZrC_p/SiC、2D C_f/ZrB_2p/SiC。探讨了三种材料在不同考核环境中的抗烧蚀机理,研究认为:在氧乙炔焰中,试样的烧蚀主要为热化学烧蚀和热物理烧蚀,同时伴有一定的气流冲刷和机械剥蚀。当试样表面温度为2200℃左右时,2D C_f/ZrB_2p/SiC表面形成的氧化熔融层黏度较高,能抵抗气流的冲刷并阻止氧向材料内部扩散,材料表现出较好的抗烧蚀性能;当表面温度为2600℃左右时,熔融物黏度明显下降,在气流冲刷下被吹除,材料的质量烧蚀率和线烧蚀率均明显增高。对于2D C_f/ZrC_p/SiC而言,当表面温度为2200℃左右时,表面还无法形成粘稠的熔融层,不利于阻隔氧向材料内部扩散;当表面温度达到2600℃左右时,烧蚀表面形成的玻璃态熔融层具有较高的黏度,能抵抗气流的冲刷和阻挡氧向材料内部破坏,材料表现出优异的抗烧蚀性能;对于2D C_f/TaC_p/SiC而言,TaC氧化产物Ta2O5的熔点只有1870℃左右,在两种考核工况下,均无法在烧蚀表面形成比较黏稠熔融层,不能对材料内部结构提供阻氧保护作用,2D C_f/TaC_p/SiC表现出较差的抗烧蚀性能。在等离子风洞中,由于考核时间短（10s）,所以热物理烧蚀、气流冲刷和机械剥蚀决定了复合材料的抗烧蚀性能。在相同的气流冲刷和机械剥蚀条件下,由于ZrB₂熔点只有3040℃,而ZrC和TaC的熔点分别高达3530℃和3880℃,所以在样品表面温度为2800℃的情况下,ZrB₂、ZrC、TaC基体的抗剥蚀能力依次增强,从而2D C_f/TaC_p/SiC复合材料表现出最好的抗烧蚀性能,2D C_f/ZrC_p/SiC次之,2D C_f/ZrB_2p/SiC最差。在等离子风洞中严重的气流冲刷和机械剥蚀作用下,复合材料中的叠层碳纤维布很容易逐层剥离,从而表现出比氧乙炔焰环境更大的质量烧蚀率和线烧蚀率。更多还原

【Abstract】 The development of hypersonic vehicles is in great need of high temperature resistant ceramic matrix composites with little ablation or even no ablation and enough mechanical properties and oxidation resistance. In this dissertation, 2D C_f/UHTC_p/SiC composites were designed and fabricated by PIP route from the viewpoint of availability and applicability. In the composites, carbon fibers were used as reinforcement to provide strength and toughness, ultra high temperature ceramics （UHTC） were used to provide high temperature and ablation resistance, SiC was used to provide oxidation resistance. The influence of PIP route and different UHTC and its content on the microstructures and properties of 2D C_f/UHTC_p/SiC composites were investigated. Also, the mechanical and anti-ablation properties of the composites were studied, and anti-ablation mechanism was discussed.The manufacturing of 2D C_f/UHTC_p/SiC composites via PIP included two steps: （1） the formation of the composites, namely fabrication of the body; （2） the densification of the composites, namely several infiltration/pyrolysis cycles were repeated to densify the body. Firstly, the formation and densification process of 2D C_f/UHTC_p/SiC composites were investigated. For 2D composites, brushing with slurry, stacking and curing of carbon fiber cloth was proper to fabricate the body of composites. The mass ratio of PCS/DVB was a key parameter to achieve a balance between content of UHTC and integrality of the body, and mPCS:mDVB=1:3 was proved to be desirable. Repeating cycles of vacuum infiltration with PCS/xylene and pyrolysis was found to be desirable for densification of the body.The influence of UHTC_p （ZrB₂, ZrC and TaC） content, molding pressure and heat treatment temperature on microstructure and properties of the composites was researched respectively. Incorporation of UHTC_p could remarkably increase the anti-ablation property of the composites. With UHTC_p contents increasing, the anti-ablation property of the composites was increased obviously. At the same time, the volume content of carbon fibers decreased, resulting in decrease in flexural strength of the composites. Increasing molding pressure could enhance mechanical and anti-ablation properties of the composites as a result of the increase of contents of UHTC_p and carbon fibers. The anti-ablation and mechanical properties could be increased further if curing was conducted with pressure.2D C_f/ZrB_2p/SiC composites, which prepared with a mass ratio (mPCS:mDVB:mZrB_2p) of 1:3:8.9, a molding-curing pressure of 7MPa, and a heat-treatment temperature of 1400℃, showed the best mechanical properties which were 252.0MPa in flexural strength and 35.5GPa in modulus. The volume content of ZrB₂, .carbon fibers and SiC in the composites were 25.5vol%, 22.6vol% and 32.5vol%, respectively. When ablated in oxyacetylene flame for 60 seconds, the surface temperature of the composites reached 2200℃. Under the circumstances, the mass loss rate and linear recession rate were 0.0260g/s and 0.0198mm/s, respectively. Increasing heat treatment temperature would improve anti-ablation property markedly, and decrease mechanical properties sharply at the same time. The composites fabricated with a heat treatment temperature of 1800℃exhibited very low mechanical properties which were 27.1MPa in flexural strength and 26.1GPa in modulus and improved anti-ablation with a linear recession rate of 0.0161mm/s and a mass loss rate of 0.0141g/s. Based the above results, it is proposed that much attention should be paid to how improve anti-ablation property not at the sacrifice of mechanical properties.2D C_f/ZrC_p/SiC composites, which prepared with a mass ratio （mPCS:mDVB:mZrC_p） of 1:3:23.3, a molding-curing pressure of 7MPa, and a heat-treatment temperature of 1600℃, showed the best mechanical properties which were 168.7MPa in flexural strength and 31.0GPa in modulus. The volume content of ZrC, carbon fibers and SiC in the composites were 33.3vol%, 20.3vol% and 26.5vol%, respectively. When ablated in oxyacetylene flame for 60 seconds, the surface temperature of the composites reached 2243℃. Under the circumstances, the linear recession rate and mass loss rate were 0.0037mm/s and 0.0073g/s, respectively.2D C_f/TaC_p/SiC composites, which prepared with a mass ratio （mPCS:mDVB:mTaC_p） of 1:3:34.0, a molding-curing pressure of 7MPa, and a heat-treatment temperature of 1600℃, showed the best mechanical properties which were 210.9MPa in flexural strength and 34.4GPa in modulus. The volume content of TaC, carbon fibers and SiC in the composites were 30.5vol%, 26.9vol% and 26.0vol%, respectively. The linear recession rate and mass loss rate were 0.0142mm/s and 0.0193g/s, respectively.The mechanical properties in room and high temperature and anti-oxidation property of the three composites were investigated. The mechanical properties of 2D C_f/UHTC_p/SiC composites were mainly decided by carbon fiber content. The tensile strengths of 2D C_f/ZrB_2p/SiC, 2D C_f/ZrC_p/SiC and 2D C_f/TaC_p/SiC were 78.5MPa, 67.4MPa and 118.9MPa, respectively. The shear strength and fracture toughness of the three 2D C_f/UHTC_p/SiC composites were～30.0MPa and～10MPa·m1/2 respectively. In order to improve the interlaminar bonding between carbon fiber cloth, z-pin through-thickness reinforcements was prepared. The resultant 2D C_f/ZrB_2p/SiC-Zpin composites showed 37.4MPa in shear strength which was increased by 20.6%. The improvement in shear strength was beneficial to the machinability and reliability of the composites. The flexural strength and flexural modulus of the resultant composites was almost the same as the unpinned sample. The compressive strengths in x, y, z directions of the three composites were all about 250.0MPa.The 2D C_f/UHTC_p/SiC composites exhibited better high temperature resistance compared with 2D C_f/SiC composites. The flexural strength of 2D C_f/ZrB_2p/SiC composites at 1800℃was 143.9MPa, 74.1% of original strength, and the flexural strength at 2000℃was only 61.8MPa. The flexural strength of 2D C_f/ZrC_p/SiC composites at 1800℃was 165.9MPa, 81.8% of original strength, and the flexural strength at 2000℃was 168.5MPa, 83.1% of original strength. The flexural strength of 2D C_f/TaC_p/SiC composites at 1800℃and 2000℃were 98.0MPa and 122.2MPa, respectively.Due to the formation of B₂O3 and Ta2O5 with self-healing ability, the 2D C_f/ZrB_2p/SiC and 2D C_f/TaC_p/SiC composites showed desirable oxidation resistance. After oxidized at 1200℃in static air, 2D C_f/ZrB_2p/SiC composites showed 184.3MPa in flexural strength, 69.2% of original strength, and 2D C_f/TaC_p/SiC composites showed 197.6MPa in flexural strength, 74.1% of original strength. However, 2D C_f/ZrC_p/SiC composites showed little strength after oxidation because the ZrO2 resulting from oxidation of ZrC had no self-healing ability.The anti-ablation properties of the three composites in two testing environments and different testing conditions were investigated. It was evident that UHTC_p played a key role in deciding anti-ablation property. The results indicated that the three composites exhibited anti-ablation property superior to 2D C_f/SiC composites due to the incorporation of UHTC_p. When ablated in oxyacetylene flame and surface temperature of composites reached 2200℃, 2D C_f/ZrB_2p/SiC composites showed the best anti-ablation property, 2D C_f/ZrC_p/SiC composites were placed in the middle, and 2D C_f/TaC_p/SiC composites showed the worst. The mass loss rate and linear recession rate of the three composites were 0.0062g/s and 0.0052mm/s, 0.0104g/s and 0.0111mm/s, and 0.0134g/s and 0.0187mm/s, respectively. In case of surface temperature of 2600℃, the mass loss rate and linear recession rate of the three composites were all increased markedly, and 2D C_f/ZrC_p/SiC composites showed the best anti-ablation property, 2D C_f/ZrB_2p/SiC composites were placed in the middle, 2D C_f/TaC_p/SiC composites showed the worst. When tested in plasma wind tunnel, the mass loss rate and linear recession rate of the three composites were further increased due to the more serious environment. Under the circumstance, 2D C_f/TaC_p/SiC composites showed the best anti-ablation property, 2D C_f/ZrC_p/SiC composites were placed in the middle, and 2D C_f/ZrB_2p/SiC composites showed the worst.Anti-ablation mechanisms of the three composites in different testing environments were discussed. In oxyacetylene flame, ablation of the composites was mainly ascribed to thermal chemical and thermal physical ablation, accompanied by airflow erosion and mechanical denudation to a certain extent. At the surface temperature of 2200℃, a layer of melted coating with high viscosity formed on the surface of 2D C_f/ZrB_2p/SiC composites, which could prevent the diffusion of oxygen and resist airflow erosion. Accordingly, the composites showed good anti-ablation property. Increasing surface temperature from 2200℃to 2600℃led to the decrease in viscosity of melted coating. In this case, the melted coating was prone to be blew away by airflow, resulting in the increase of mass loss rate and linear recession rate. As for 2D C_f/ZrC_p/SiC composites, viscous coating could not form until surface temperature of the composites reached 2600℃. Consequently, 2D C_f/ZrC_p/SiC composites showed better anti-ablation property at surface temperature of 2600℃than 2200℃. Viscous coating could not form on surface of 2D C_f/TaC_p/SiC composites at surface temperature of 2200℃and 2600℃because the melting point of Ta2O5 derived from oxidation of TaC is 1870℃. As a result, the composites exhibited the worst anti-ablation property.In plasma wind tunnel, thermal chemical ablation can be ignored because testing time is only 10 seconds. So, thermal physical ablation, airflow erosion and mechanical denudation play a significant role in determining anti-ablation property of the three composites. The melting points of ZrB₂, ZrC and TaC are 3040℃, 3530℃and 3880℃, respectively. Accordingly, when surface temperature reached 2800℃, 2D C_f/TaC_p/SiC composites showed the best anti-ablation property, 2D C_f/ZrC_p/SiC composites were placed in the middle and 2D C_f/ZrB_2p/SiC composites exhibited the worst, which were decided by anti-denudation ability of ZrB₂, ZrC and TaC at 2800℃. It was easier for stacked carbon fiber cloths to be blew away in plasma wind tunnel due to more serious airflow erosion and mechanical denudation than in oxyacetylene flame. As a result, the composites showed worse anti-ablation property in plasma wind tunnel.更多还原