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题名	Cf/SiC表面RE2SiO5/LaMgAl11O19(RE=Yb,Er)新型热障涂层的抗氧化行为与失效机理研究
作者	王盈
学位类别	硕士
答辩日期	2015-05
授予单位	中国科学院研究生院
授予地点	中国科学院长春应用化学研究所
导师	曹学强 ; 邹兵林
关键词	Cf/SiC复合材料 热障涂层 大气等离子喷涂 氧化保护 失效机理
中文摘要	Cf/SiC抗氧化抗烧蚀性能较差, 涂层防护是克服Cf/SiC性能不足的有效途径。现代超音速武器装备要求Cf/SiC表面涂层能够经受2273K火焰灼烧并对基底提供良好的热防护。本文设计了新型稀土复合氧化物热障涂层，通过等离子喷涂技术制备涂层，有效地解决了Cf/SiC在2273K火焰灼烧时的热防护难题，为突破新一代高超音速武器装备对Cf/SiC高温热防护需求瓶颈奠定一定的理论基础。 通过高温固相反应合成了Er2SiO5，Yb2SiO5和LaMgAl11O19 (LMA)粉末，并采用大气等离子喷涂技术对粉末进行喷涂，成功地在C/SiC表面制备了RE2SiO5/LMA (RE=Yb, Er)双陶瓷层热防护涂层。涂层与基体以及陶瓷层之间界面结合良好，涂层分布均匀，RE2SiO5内陶瓷层组织致密。 发现在~2273 K高温火焰循环灼烧下，RE2SiO5/LMA (RE=Er, Yb)涂层显著地提高了Cf/SiC基体的抗氧化性能。11次热循环后，未喷涂Cf/SiC样品氧化失重率高达20.6%，而单面喷涂了Er 2SiO5/LMA和Yb 2SiO5/LMA涂层的Cf/SiC样品，其氧化失重率仅分别为4.5%和4.1%。Cf/SiC本身的孔洞和裂纹导致了样品轻微氧化。11次热循环后，涂层与基体之间界面结合良好。 揭示了Cf/SiC表面RE2SiO5/LMA(RE=Yb,Er)涂层热循环失效机理如下：首先，RE2SiO5和LMA双陶瓷层之间原子相互扩散导致界面发生化学反应，使涂层发生液相烧结，形成了致密组织结构；其次，基体氧化生成的气体由于涂层的致密组织结构，来不及从涂层中逸出，形成了气泡；随后，随着气体产生，烧结涂层中气泡长大，使涂层产生了鼓包和裂纹，这显著加速了涂层和基体之间的剥离和裂纹的蔓延，从而造成涂层失效。 发现Cf/SiC表面Yb2SiO5/LMA涂层的热循环寿命主要取决于Yb2SiO5陶瓷层厚度。当Yb2SiO5层厚度从50μm增加至100μm时，涂层热循环寿命从130次降低为35次，而当Yb2SiO5层厚度继续增加至200μm时，涂层热循环寿命降低为仅有2次。揭示了Yb2SiO5层厚度对涂层热循环寿命的影响机理。Yb2SiO5 与基体的热膨胀不匹配以及1415oC时Yb2SiO5的体积收缩决定了涂层的热循环寿命。当Yb2SiO5层较薄时（如≤50μm），Yb2SiO5层热膨胀不匹配和体积收缩产生的热应力较小，涂层失效是由于涂层烧结和气泡长大引起的，涂层寿命较长；而当Yb2SiO5层较厚时（如≥100μm），由于Yb2SiO5层与基体的热膨胀不匹配和体积收缩形成了较大的界面残余热应力，涂层寿命显著降低。 揭示了RE2SiO5/LMA(RE=Er,Yb)涂层可以在短时间内（如几十分钟）对Cf/SiC复合材料提供良好的热防护。
英文摘要	Cf/SiC composites are susceptible to ablation and oxidation in the high-temperature oxidizing environment, and it has been proven that the coating protection is a better approach to improve the oxidation and ablation resistance of Cf/SiC composites. With the development of modern hypersonic weapons, it is desired that the coating could endure a flame with temperature up to 2273 K and protect Cf/SiC from degradation by the flame. In this project, the novel thermal barrier coatings based on rare-earth oxides composites were designed and deposited on Cf/SiC substrate by atmospheric plasma spraying, which had a good protection for the Cf/SiC substrate against the flame. It is expected that this study could provide valuable theoretical basis for the breakthrough of bottleneck of the high temperature thermal protection required by the new generation of hypersonic weapons for the Cf/SiC composites. The Er2SiO5, Yb2SiO5 and LaMgAl11O19 (LMA) powders were produced by solid state reactions at high temperatures. The synthesized powders were subjected to atmospheric plasma spraying and thus the RE2SiO5/LMA (RE=Er, Yb) coatings were successfully fabricated on the C/SiC composites. Good interfacial bonding was present between the substrate and coatings as well as between the ceramic layers in the coatings, the coatings uniformly distrubuted on the substrate, and the inner ceramic layer of RE2SiO5 seemed to be dense. The RE2SiO5/LMA (RE=Yb, Er) coatings significantly improved the oxidation resistance of the Cf/SiC composites exposed to gas flame with temperature about 2273 K. The weight losses for the samples coated on one–side with the Er2SiO5/LMA and Yb2SiO5/LMA coatings were only 4.1% and 4.5% after 11 cycles, respectively. For the uncoated sample, the weight loss was as high as 20.6%. The holes and cracks in the green C/SiC composites should be responsible for the slight oxidation of the coated sample. Good interfacial bonding between the substrate and the coatings was retained after 11 cycles. The failure mechanism of RE2SiO5/LMA (RE=Yb,Er)coatings on the Cf/SiC substrate during thermal cycling is presumed to be as follows: firstly, liquid sintering occurred in the coating, which may be as a successive result of the reactions resulted from the interdiffusion of atoms between RE2SiO5 layer and LMA layer, and therefore, a dense microstructure of the coating was obtained. Secondly, the produced gases from the oxidation of the substrate did not promptly escape from the sintered coating due to the dense microstructure, which brought the formation of the bubbles; subsequently, the growing bubbles because of the increasing gases in them made the sintered coating give rise to the bumps and cracks, which significantly accelerated the delamination of the coating from the substrate and thus the induced propagating of the cracks, as a result, the coating was peeled off. The thermal cycling life of Yb2SiO5/LMA coating is significantly dependent on the Yb2SiO5 layer thickness, which decreased from 130 cycles to 35 cycles when the Yb2SiO5 layer thickness increased from 50 ?m to 100 ?m. Further increasing Yb2SiO5 layer thickness to 200 ?m made the thermal cycling life decrease to 2 cycles. The influencing mechanism of Yb2SiO5 layer thickness for the thermal cycling life was clarified. The CTE mismach between the substrate and Yb2SiO5 layer and the volume contraction of Yb2SiO5 after 1415 oC are the crucial factors manipulating the thermal cycling life of the coating. For thin Yb2SiO5 layer (e.g. ≤50 ?m), the thermal stress by the CTE mismach and the volume contraction of Yb2SiO5 is considered to be very small, the failure of Yb2SiO5/LMA coating resulted from the reaction sintering of the coating and the formation of bubbles between the substrate and the coating, and so the thermal cycling life of the coating is long. For thicker Yb2SiO5 layer (e.g. ≥100 ?m), the larger interface thermal stress was produced between the substrate and Yb2SiO5 layer because of the CTE mismach and the volume contraction of Yb2SiO5, which significantly decreased the thermal cycling life of the coating. The RE2SiO5/LMA (RE=Yb,Er) coatings are attractive for short–term applications (e.g. tens of minutes) of C/SiC composites exposed to gas flame with high temperature (e.g. ~2273 K).
语种	中文
公开日期	2016-05-03
内容类型	学位论文
源URL	[http://ir.ciac.jl.cn/handle/322003/64468]
专题	长春应用化学研究所_长春应用化学研究所知识产出_学位论文
推荐引用方式 GB/T 7714	王盈. Cf/SiC表面RE2SiO5/LaMgAl11O19(RE=Yb,Er)新型热障涂层的抗氧化行为与失效机理研究[D]. 中国科学院长春应用化学研究所. 中国科学院研究生院. 2015.

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