【作者】 付前刚；

【导师】 李贺军；

【作者基本信息】 西北工业大学 ， 材料学， 2007， 博士

【摘要】 炭／炭（C／C）复合材料具有优异的高温性能，在航空航天等领域有极其广阔的应用前景。高温易氧化是C／C复合材料作为热结构材料使用的瓶颈问题，而防氧化涂层是解决这一难题的有效手段。本文以研制C／C复合材料高温防氧化涂层为研究目标，采用包埋法、料浆法等制备了SiC晶须增韧硅化物涂层以及SiC／玻璃双层涂层，借助XRD、SEM、EDS等测试手段分析了涂层的相组成、微观形貌与元素分布，考察了涂层的防氧化与抗热震性能，研究了热震与氧化对涂层试件力学性能的影响，并对涂层的防氧化机理与失效原因进行了研究，主要研究内容与结果如下：采用两次包埋法制备出SiC-CrSi₂双相涂层，研究了该涂层的微观结构及防氧化性能，着重探讨了Si／Cr比对涂层微观结构及抗氧化性能的影响，表明CrSi连续相有效填充了SiC涂层中的孔隙与裂纹，提高了涂层的致密性；随着包埋原料中Cr／Si质量比的增大，涂层中SiC含量逐渐减少，CrSi₂连续相含量增加，裂纹尺寸增大；防氧化能力表现出先提高后降低的趋势。采用料浆法与包埋法制备出SiC晶须增韧SiC-CrSi₂涂层，研究了SiC晶须含量对涂层微观结构、抗氧化性能及抗热震性能的影响；讨论了SiC晶须增韧SiC／Si-Cr涂层试件在不同温度下的氧化行为，并对涂层的氧化失效机制进行了分析，结果表明：随着料浆中SiC晶须含量的增加，制备的SiC晶须增韧SiC-CrSi₂涂层裂纹尺寸减小，厚度降低，涂层中CrSi₂相含量先增后减，涂层防氧化能力表现出先提高后下降的趋势；当SiC晶须含量为15wt．％时，涂层具有较好的防氧化与抗热震性能，且该涂层在1500℃时表现出相对较好的防氧化能力，氧化50小时后涂层试件失重率仅为0.66％；涂层试件的氧化失重主要是山于在高温←→室温的热循环过程中氧通过涂层中的裂纹扩散至基体表面氧化C／C所引起的。采用料浆法与包埋法制备出SiC晶须增韧Si-SiC涂层，着重研究SiC晶须含量对涂层微观结构、抗氧化性能及抗热震性能的影响；并对涂层制备工艺进行了优化，研究SiC晶须增韧Si-SiC涂层试件热疲劳行为，分析涂层的氧化失效机制，结果表明：涂层中游离硅的存在有利于阻碍裂纹的扩展，在涂层与基体界面处形成了一层SiC-C梯度过渡层；SiC晶须含量为10wt．％制备的SiC晶须增韧Si-SiC涂层具有优良的防氧化性能，在1500℃静态空气中可对C／C复合材料有效保护310小时以上，在1600℃静态空气中可对C／C复合材料有效保护128小时；涂层试件经历1600℃静态空气3分钟←→100℃沸水热循环50次后试件失重2.76％，弯曲强度保持率为74.5％，其失重和弯曲强度下降是由于C／C基体被氧气和水蒸气氧化引起的。采用料浆法与包埋法相结合，在C／C复合材料表面制备出SiCw晶须增韧MoSi₂-SiC-Si多相涂层，探讨了晶须含量、制备温度等对涂层微观结构及防氧化性能的影响规律，研究了涂层对试件力学性能的影响，结果显示：当SiCw含量为10wt．％，料浆法制备温度为1800℃，包埋法制备温度为2000℃所制备的涂层具有较为理想的防氧化性能，1500℃静态空气中氧化240小时后的氧化失重率仅为0.33％；试件的弯曲强度提高，经1500℃←→室温热震10次以及1500℃氧化60分钟后，涂层试件的弯曲强度保持率分别为81.97％和89.63％，涂层试件氧化后弯曲强度下降主要是由于环境中的氧通过涂层中的裂纹与孔洞等缺陷扩散而氧化C／C基体所引起的。采用两次包埋法制备出B₂O₃改性SiCw-MoSi₂-SiC涂层，研究了B₂O₃含量对涂层性能的影响，结果表明，当B₂O₃含量为5％时，涂层具有较好的防氧化能力，经1500℃氧化242小时后试件增重0.18％。该涂层在1600℃←→400℃变温氧化阶段防氧化能力较差的原因是涂层在800℃附近存在尺寸较大的开放性裂纹。以硅溶胶为粘结剂，以B₄C和玻璃粉为主要原料，采用料浆法在C／C复合材料SiC内涂层表面制备出适用于900℃防氧化的玻璃外涂层，研究了B₄C含量及SiC内涂层结构对涂层性能的影响，分析了涂层的防氧化失效原因，结果显示：B₄C含量为10wt．％以及SiC内层为采用两步包埋法制备的致密涂层时，SiC／玻璃涂层具有较好的防氧化性能，试件在900℃静态空气中氧化100小时后失重率仅为0.14％，玻璃涂层在氧化温度下的缓慢挥发是涂层试件在氧化过程中表现为微量失重的主要原因。采用料浆法在多孔β-SiC过渡层表面制备出适用于1300℃防氧化的玻璃密封层，研究了涂层的微观结构及防氧化性能，分析了涂层氧化失效机制。密封层的结构为MoSi₂相分散于硼硅酸盐玻璃相中；带有β-SiC／玻璃密封层的C／C试件在1300℃的静态空气中氧化150小时以及经20次1300℃←→室温急冷急热循环后，涂层试样的氧化失重率仅为1.07％；涂层试件的氧化主要是由于氧通过涂层中的裂纹扩散至基体表面而氧化基体，以及部分区域的涂层脱落所引起的。直接以SiO₂、B₂O₃、Al₂O₃等为原料，采用料浆法在C／C复合材料SiC内涂层表面制备出适用于1500℃防氧化的玻璃涂层，研究了涂层的微观结构及防氧化性能，分析了涂层氧化失效机制。该涂层可在1500℃空气中对C／C复合材料有效保护140小时，试样失重率仅为0.98％；该涂层试件的氧化失重主要是玻璃涂层的开裂以及涂层表面气孔的形成引起的。分别对SiC晶须增韧Si-SiC／玻璃涂层及SiC晶须增韧MoS₂-SiC-Si／SiC／玻璃涂层的高温抗冲刷性能进行了研究，结果表明，以上两种涂层可在1500℃风洞环境下对C／C复合材料有效保护16和53小时，涂层在热冲击以及气流冲击的恶劣环境下的开裂是其在高温燃气冲刷环境中防氧化失效的主要原因。更多还原

【Abstract】 Carbon/carbon （C/C） composites are provided with excellent properties at high temperature, and are considered as the most promising candidate materials for high temperature application such as in aviation, space flight fields. However, C/C composites are prone to oxidize at high temperature, which limits their applications as high-temperature structural materials. Anti-oxidation coatings are considered to be an effective method for preventing C/C composites from oxidation at high temperature. In order to exploit the oxidation protective coatings using at high temperature, SiC whisker-toughened silicides coating and SiC/glass double-layer coating were prepared by pack cementation and slurry. The phase composition, microstructure and element distributing of the as-prepared coatings were characterized by XRD, SEM and EDS analyses. The oxidation protective ability and thermal shock resistance of the as-obtained coatings were investigated. Moreover, the anti-oxidation mechanism and the failure reason of the coatings were also discussed. The main contents and conclusions are listed as follows:The SiC-CrSi₂ double-phase coating was produced by a two-step pack cementation technique. The microstructure and oxidation protective ability of the coating were investigated. The effect of Si/Cr with the different weight ratio on the microstructure and anti-oxidation property was discussed. The results show that the CrSi₂ phase can be filled in the holes and cracks of the SiC inner layer, resulting in the dense structure of the coating. With the increasing of Cr/Si in the initial pack power, the content of SiC phase in the coating decreases, CrSi₂ phase and the size of the cracks in the coating increase gradually, and the oxidation protective ability of the coating increase firstly and decrease later.SiC whisker （SiCw） toughened SiC-CrSi₂ oxidation protective coating was prepared by slurry and pack cementation. The effects of SiC whisker content on the microstructure, oxidation protective ability and thermal chock resistance were investigated. The oxidation behavior of the SiC whisker-toughened SiC-CrSi₂ coating at different temperatures were discussed and the failure mechanism of the coating was also analyzed. With the increasing of the SiCw content, the size of the cracks in the coating and the thickness of the coating decease, while the CrSi₂ content in the coating and the oxidation protective ability of the coating exhibit the trend of increase first and decrease afterwards. The coating containing with 15wt.% SiCw exhibits excellent oxidation protective ability and thermal shock resistance. The weight loss of the coated specimens was only 0.66% aider oxidation for 50h at 1500℃in air. The failure of the coated specimens mainly results from the oxidation between the oxygen diffusing though the cracks in the coating and C/C matrix during the thermal cycles between high temperature and room temperature.SiCw toughened Si-SiC coating was obtained by slurry and pack cementation technique. The effects of the SiCw content on the microstructure, oxidation resistance and thermal shock resistance were investigated and the preparing process was also optimized. The effect of the thermal shock on the mechanical property of the coated samples was discussed. The SiCw toughened Si-SiC coating is provided with excellent oxidation resistance, and can protect C/C composites from oxidation for more than 310 h at 1773℃and for 128h at 1873℃in air. After thermal cycle between 1873K air and 373K boiling water for 50 times, the weight loss of the SiC coated sample was 2.76% and the remaining strength percentage was 74.5%. The decreasing of the flexural strength during the thermal cycle was primarily due to the oxidation between the coated samples and oxygen or vapor.SiCw toughened MoSi₂-SiC-Si multi-phase coatings were produced on the surface of C/C composites by slurry and pack cementation. The effects of the SiCw content and the preparing temperature on the microstructure and oxidation protective ability of the as-obtained coating were investigated. The effect of the coating on the mechanical property of the samples was also discussed. The results show that when the SiCw content is 10wt.%, the preparing temperatures for the slurry method and pack cementation are 1800℃and 2000℃respectively, the coating is provide with excellent oxidation resistance, which could effectively protect C/C composites at 1500℃for 240h and the corresponding weight loss was only 0.33%. The flexural strength of the specimens increases after they are coated. The percentage of remaining flexural strength of the coated specimens were 81.97% and 89.63% respectively after thermal shock between 1500℃and room temperature for 10 times and isothermal oxidation at 1500℃for 60 min. The decreasing of the flexural strength is mainly attributed to the formation of the cracks and holes in the coating, through which the oxygen can diffuse into the C/C matrix and oxidize the C/C matrix.SiCw toughened SiCw-MoSi₂-SiC coating modified by B₂O₃ was produced by a two-step pack cementation technique. The effect of B₂O₃ content on the property of the coating was investigated. The result shows that as the B₂O₃ content is 5%, the coating exhibits better oxidation resistance. After oxidation at 1500℃for 242 hours, the weight gain of the coated specimens is 0.18%. The poor oxidation resistance at the changing temperature stage from 1600℃to 400℃is due to the formation of the open cracks at about 800℃.Using silicon-sol as the binder, glass power and B4C particles as main raw materials, the glass outer coating applied at 900℃was prepared on the surface of SiC inner coating. The effects of the B4C content and the structure of the SiC inner coating on the oxidation protective ability of the as-obtained coating were investigated. The failure reason of the coated specimens was also discussed. The results show that as the B4C content is 10 wt.% and the SiC inner layer is dense structure obtained by two-step pack cementation, the SiC/glass coating exhibits excellent oxidation protective ability, which can protect C/C composites at 900℃in air for 100h and the weight loss is only 0.14%. The slight weight loss is mainly attributed to the gradual volatilization of the glass coating during oxidation test.The glass oxidation protective coating for application at 1300℃was prepared on the surface of a porousβ-SiC bonding layer by slurry. The microstructure and oxidation resistance of the coated specimens was investigated. The oxidation mechanism of the coating was also discussed. The sealing layer is composed of the borosilicate glass phase with the dispersion of MoSi₂ particles. The weight loss of theβ-SiC/glass coated specimens is only 1.07% after oxidation for 150 hours at 1300℃and thermal cycles between 1300℃and room temperature for 20 times. The oxidation of the coated specimens mainly results from the cracks in the coating and the debonding of some glass coating.Using SiO₂, B₂O₃ and Al₂O₃ as the original materials, the glass coating for application at 1500℃was prepared on the surface of the SiC coated C/C composites by slurry. The microstructure and oxidation resistance of the coating was investigated. The oxidation mechanism of the coated specimens was also discussed. The coating can effectively protect C/C composites at 1500℃for 140 hours and the corresponding weight loss was only 0.98%. The weight loss of the coated specimens is mainly attributed to the crazing of the glass coating and the formation of holes on the coating surface.The oxidation behaviors of C/C composites with SiCw-Si-SiC/glass coating and SiCw-MoSi₂-SiC-Si/SiC/glass coating in combustion gas environment at 1512℃were studied respectively. The oxidation mechanism of the coated specimens was also nalyzed. The SiCw-Si-SiC/glass coating and SiCw-MoSi₂-SiC-Si/SiC/glass coating can protect C/C composites in wind tunnel environment at 1500℃for 16h and 53h respectively. The cracking of the coating under thermal impact and airflow impact environment is the main reason for the anti-oxidation failure of the coating.更多还原