化学气相沉积SiC和ZrC涂层的制备及抗烧蚀性能

发布时间：2018-05-25 18:59

本文选题：碳/碳复合材料 + 抗烧蚀涂层　；参考：《西北工业大学》2015年博士论文

【摘要】：碳/碳（C/C）复合材料由于其优异的高温性能，在航空航天领域具有极其广泛的应用前景。但该材料在370℃以上有氧环境下的快速氧化限制了其作为航空航天热结构、热防护材料的应用，涂层技术是解决该问题的有效手段。SiC、ZrC因其高熔点和良好的高温稳定性，成为C/C复合材料表面抗烧蚀涂层的理想材料。本文采用低压化学气相沉积法（Low Pressure Chemical Vapor Deposition,LPCVD）在C/C复合材料和碳纤维表面分别制备了SiC、ZrC涂层，研究了工艺参数对涂层微观结构的影响；通过氧乙炔焰考察和研究了涂层在循环烧蚀和不同热流量烧蚀条件下的抗烧蚀性能和烧蚀机理；针对ZrC涂层和C/C基体之间的热膨胀失配，设计并制备了SiC/ZrC复合涂层和SiC/ZrC/SiC多层涂层，以缓解ZrC涂层的热膨胀失配，，提高涂层的抗烧蚀性能；采用X-射线衍射仪、扫描电镜、透射电镜及氧乙炔焰烧蚀等分析和测试手段对涂层的微观结构和烧蚀性能进行研究，本文的主要研究内容和结果如下：以MTS-H2-Ar为反应体系，采用LPCVD法在不同沉积温度和H2/MTS摩尔比值下分别在C/C复合材料表面和碳纤维表面制备了SiC涂层，通过对涂层形貌的分析，获得了沉积温度和H2/MTS摩尔比对SiC涂层结构的影响规律。随着沉积温度的升高， SiC颗粒生长速率逐渐加快，颗粒尺寸差别逐渐明显，涂层表面粗糙度增加；随着H2/MTS摩尔比的增加，SiC颗粒形核作用逐渐增强，颗粒尺寸逐渐减小且分布均匀，涂层致密度增加；C/C表面和碳纤维表面SiC涂层结构均以孪晶和层错为主；在CVD-SiC的生长过程中，存在PAN碳纤维表面沟槽和沉积SiC层的两种模板效应，SiC涂层随厚度的增加从层状/岛状生长逐渐转变为层状+岛状生长模式；氧乙炔焰烧蚀环境下，SiC涂层可以提高C/C复合材料的短时抗烧蚀性能；随着烧蚀循环次数的增加，热震作用导致SiO2层中缺陷的尺寸和数量进一步增加，SiO2层中的微孔逐渐转变为破坏性的孔洞，加剧了涂层的氧化损失和火焰剥蚀损失，导致涂层逐渐失效。涂层烧蚀中心区域的烧蚀行为以氧化腐蚀和机械剥蚀为主，烧蚀过渡区域和边缘区域的烧蚀行为以氧化腐蚀为主；随着烧蚀热流量的增加，烧蚀中心区域SiC涂层的烧蚀行为由以氧化腐蚀和机械剥蚀为主转变为以气化为主，SiO2层的损耗随着烧蚀区域逐渐远离烧蚀中心而不断降低，试样质量烧蚀率和线烧蚀率明显升高。以ZrCl4-C3H6-Ar-H2为反应体系，采用LPCVD法分别在C/C复合材料和碳纤维表面制备了ZrC涂层，涂层的主要成分为立方相ZrC。随着沉积温度升高，涂层颗粒生长速率增加，涂层生长均匀性有所降低，择优取向从（111）向（200）面转变；随着H2浓度的增加，涂层颗粒尺寸逐渐减小且变得均匀，择优取向从（111）向（200）向（220）面转变，涂层致密性提高；随着沉积位置距进气口距离的增加，反应物浓度逐渐降低，涂层形核作用增强，颗粒尺寸逐渐减小，涂层生长均匀性增加。采用氧乙炔焰测试了C/C复合材料表面ZrC涂层的抗烧蚀性能并分析了其烧蚀机理。结果表明：不同沉积温度下制备的ZrC涂层的抗烧蚀性能随着沉积温度的升高而提高；在1350℃温度下制备的涂层表现出最佳的抗烧蚀性能；在烧蚀过程中，ZrO2层和ZrCxOy层有效地阻碍了氧气在涂层中的扩散并及时愈合烧蚀过程中出现的孔洞和微裂纹等缺陷，同时削弱了火焰对涂层的机械剥蚀作用；不同H2浓度下制备的ZrC涂层的抗烧蚀性能随着H2浓度的升高而先提高后降低；纳米结构涂层通过纳米粒子增韧涂层的作用，降低火焰对涂层的剥蚀作用，提高了涂层抗烧蚀性能；在部分涂层的烧蚀过程中生成了ZrO2纳米棒，ZrO2纳米颗粒在纳米棒的生长中发挥了催化剂的作用并提供了纳米棒的生长基底，纳米棒的生长机制为V-L-S和OAG机制；在循环烧蚀条件下，ZrC涂层存在两种烧蚀模式：表面烧蚀和内部烧蚀。随着烧蚀循环次数的增加，涂层中缺陷的数量和尺寸由于热震作用而逐渐增加，涂层由表面烧蚀转变为内部烧蚀，ZrC在烧蚀过程中的结构转变过程为ZrC→ZrCxOy→ZrO2；在不同热流量烧蚀条件下，随着烧蚀热流量的增加，氧气在涂层中的扩散量增加，ZrC→ZrCxOy→ZrO2的转变过程随着热流量的增高而加速。通过涂层设计，采用LPCVD法在C/C表面制备SiC/ZrC复合涂层和SiC/ZrC/SiC多层涂层，内层SiC有效的缓解了ZrC层和C/C基体的热膨胀不匹配，增强了涂层和C/C基体的结合，外层SiC延缓了火焰和ZrC层的接触，SiO2层的损耗带走大量的热量并降低了涂层表面温度，进一步提高了C/C复合材料的抗烧蚀性能。
[Abstract]:Carbon / carbon (C/C) composites have an extremely wide range of applications in the field of Aeronautics and Astronautics due to their excellent high temperature properties. However, the rapid oxidation of this material under the oxygen environment above 370 degrees centigrade limits its application as the thermal structure of Aeronautics and Astronautics and the application of thermal protection materials. The coating technology is an effective means to solve this problem,.SiC and ZrC because of its high melting. Point and good high temperature stability are ideal materials for ablative coating on the surface of C/C composite.
The low pressure chemical vapor deposition (Low Pressure Chemical Vapor Deposition, LPCVD) was used to prepare SiC, ZrC coating on the surface of C/C composite and carbon fiber, and the effect of process parameters on the microstructure of the coating was studied. The coating was investigated and studied under the condition of cyclic ablation and different heat flow ablation through oxygen acetylene flame. In order to alleviate the thermal expansion mismatch of the ZrC coating and improve the ablative performance of the coating, the SiC/ZrC composite coating and the SiC/ZrC/SiC multilayer coating were designed and prepared for the thermal expansion mismatch between the ZrC coating and the C/C matrix. The X- ray diffractometer, scanning electron microscope, transmission electron microscope and oxyacetylene flame ablation were used to analyze the corrosion resistance of the coating. The microstructure and ablation properties of the coating were studied by means of testing. The main contents and results of this study are as follows:
The SiC coating was prepared on the surface of C/C composite and on the surface of carbon fiber on the surface of C/C composite and carbon fiber on the surface of C/C composite with MTS-H2-Ar as the reaction system. By analyzing the morphology of the coating, the influence of the deposition temperature and molar ratio of H2/MTS to the structure of the SiC coating was obtained. With the increase of the deposition temperature, the SiC particles were produced. With the increase of the particle size, the surface roughness of the coating increases. With the increase of the H2/MTS molar ratio, the nucleation of SiC particles increases gradually, the particle size decreases and the distribution is uniform, the density of the coating increases, and the structure of the SiC coating on the surface of C/C and the surface of carbon fiber is mainly twinning and stacking, and in CVD-SiC During the growth process, there are two template effects on the surface groove of PAN carbon fiber and the deposition of SiC layer. As the thickness increases, the SiC coating gradually changes from the layer / island growth to the layered + island growth mode. Under the oxygen acetylene flame ablative environment, the SiC coating can improve the short-time anti ablation performance of the C/C composite; with the increase of the times of the ablation cycle, the SiC coating can be improved. The thermal shock causes the size and quantity of the defects in the SiO2 layer to be further increased, and the micropores in the SiO2 layer are gradually transformed into destructive holes, which aggravate the oxidation loss and the loss of the flame erosion, resulting in the gradual failure of the coating. The ablation behavior of the center area of the coating is mainly oxidized and mechanical denudation, and the transition area and edge are ablated. The ablative behavior of the rim region is mainly oxidation corrosion. With the increase of the ablation heat flux, the ablation behavior of the SiC coating in the central area of the ablation center is mainly converted from oxidation corrosion and mechanical denudation to gasification. The loss of the SiO2 layer decreases with the ablation zone gradually away from the ablation center, and the mass ablative rate and the line ablation rate of the sample are clear. Increase significantly.
With ZrCl4-C3H6-Ar-H2 as the reaction system, the ZrC coating was prepared on the surface of C/C composite and carbon fiber by LPCVD. The main component of the coating was cubic ZrC., with the increase of the deposition temperature, the growth rate of the coating particles increased, the uniformity of the coating growth decreased, the preferred orientation changed from (111) to (200) surface, with the increase of H2 concentration. Adding, the size of the coated particles gradually decreases and becomes uniform. The preferred orientation changes from (111) to (200) to (220) surface, and the coating densification increases. With the increase of the distance from the inlet to the inlet, the concentration of the reactant decreases gradually, the nucleation of the coating increases, the particle size decreases, and the uniformity of the coating increases.
The ablative properties of the ZrC coating on the surface of C/C composites were measured by oxyacetylene flame and its ablation mechanism was analyzed. The results showed that the ablative performance of the ZrC coating prepared at different deposition temperatures increased with the increase of the deposition temperature; the coating prepared at 1350 C showed the best ablative performance; in the ablation process, the corrosion resistance of the coating was improved. The ZrO2 layer and the ZrCxOy layer effectively obstruct the diffusion of oxygen in the coating and heal the holes and micro cracks in the ablation process in time, and weaken the mechanical denudation of the flame to the coating. The ablative properties of the ZrC coating prepared at different H2 concentrations increase first and then decrease with the increase of the concentration of H2; The coating was toughened by nano particles, the denudation effect of flame on the coating was reduced and the ablative performance of the coating was improved. ZrO2 nanorods were formed during the ablation process of some coatings. ZrO2 nanoparticles played the role of the catalyst in the growth of nanorods, and the growth of nanorods. The mechanism is V-L-S and OAG mechanism. Under cyclic ablative conditions, there are two kinds of ablation modes in ZrC coating: surface ablation and internal ablation. With the increase of the number of ablation cycles, the number and size of the defects in the coating gradually increase due to thermal shock, the coating changes from surface ablation to internal ablation, and the structure transformation of ZrC in the process of ablation. The process is ZrC - ZrCxOy - ZrO2, and the diffusion of oxygen in the coating increases with the increase of the ablation heat flow, and the transition process of ZrC to ZrCxOy to ZrO2 accelerates with the increase of heat flux under different heat flow ablation conditions.
Through the coating design, the SiC/ZrC composite coating and SiC/ZrC/SiC multilayer coating are prepared by LPCVD method on the C/C surface. The inner layer SiC effectively relieves the thermal expansion mismatch between the ZrC layer and the C/C matrix, enhances the combination of the coating and the C/C matrix. The outer SiC delaying the contact between the flame and the ZrC layer, the loss of the SiO2 layer takes away a large amount of heat and reduces the coating. Surface temperature further enhances the ablation resistance of C/C composites.
【学位授予单位】：西北工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB332

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