溶胶-凝胶涂层在超重力场作用下的致密化机理及其抗腐蚀特性研究

The purpose of the proposal is to resolve the important scientific issue that sol-gel derived coatings are not dense enough for its application to provide metallic substrate with effective corrosion resistance. Based on previous research progress that rather denser sol-gel derived coatings are obtained by changing the movement of coatings' component via external force transferred with medium powder during the solidification stage of the coatings and by driving permeating and sealing behavior of sealant's component via effect of electric field, a solution to improve density and corrosion resistance of sol-gel derived coatings through permeating and sealing the coatings with assistance of external force imposed by super-gravity field is proposed. In macroscopic view, the effect of super-gravity field can drive sealant's component to deposit at the bottom of hole or crack preferentially to fill the defects gradually till the surface of the coatings and forming a covering layer; in microscopic view, it can change the movement of sealant's component during solidification stage of the sealant and improve solute filling extent on the position occupied previously by the solvent. Thus, The more effective densification for the coatings is achieved. With the study on the process that the densification of sol-gel derived coatings is influenced by the effect of super-gravity field, the mechanism of the influence is revealed, internal relationship between the densification that is assisted with the effect of super-gravity field and corrosion resistance of the coatings is well explained, and the theoretical foundation and technological approach to perform excellent corrosion resistance of the coatings are provided. The expected results of the proposal will meet the requirement of corrosion resistance in the field of aviation, aerospace, nuclear fusion and ADS with effective resolutions. The technology of densifying coatings in the proposal would have a future of wider application.

本项目针对溶胶－凝胶涂层不够致密，难以为金属基体提供有效腐蚀防护这一关键科学问题，在前期通过介质粉传递所施外力改变涂层组分在固化过程的运动行为以及通过电场作用力驱动密封剂组分的渗封行为获得较致密溶胶-凝胶涂层的基础上，提出采用超重力场施加外力协助渗封处理溶胶-凝胶涂层，提高涂层的致密度和抗腐蚀性能的方法。超重力场作用在宏观上可驱使密封剂优先沉积于孔洞或裂缝底部并逐渐填充至缺陷表面再形成覆盖层，在微观上可改变密封剂组分在固化过程的运动行为，提高溶质对周围溶剂占据空间的填充程度，从而获得更好的致密化效果。通过研究超重力场作用对致密化行为的影响规律，揭示相应的作用机理，阐明超重力场协助致密化处理和涂层抗腐蚀性能的内在联系，提供获得最佳抗腐蚀效果的理论依据和技术途径。本项目的成果有望为航空、航天、核聚变及核嬗变等关键工程的抗腐蚀需求提供有效的解决途径，所研究的涂层致密化技术具有广泛的应用前景。

首先研究溶胶-凝胶涂层的结构对其防护性能的影响。制备表面平整，厚度均匀的ZrO2、Al2O3和Al2O3-ZrO2微叠涂层，8次提拉的厚度约150 nm。高温循环氧化测试结果表明，涂层的防护性能随厚度增加而提高；Al2O3-ZrO2微叠涂层能够结合ZrO2涂层与金属基体热匹配性能好以及Al2O3涂层的氧扩散系数低的优点，表现出比二者更好的综合抗高温氧化防护性能。Al2O3层和ZrO2层的排列组合模式也对Al2O3-ZrO2微叠涂层得抗高温氧化防护性能产生影响，当总层数和组分层数相同时，相邻氧阻挡层的厚度越大，微叠涂层的抗高温氧化防护性能越好。. 采用复合料浆热压滤法可制备厚度在数十到数百微米可控的YSZ/YSZ、Al2O3/YSZ、Al2O3/YSZ-Al2O3和Al2O3/Al2O3复合涂层。复合涂层由具有空间网络结构的YSZ或Al2O3包覆颗粒状YSZ或/和Al2O3组成。含有适量YSZ颗粒的Al2O3/YSZ-Al2O3复合涂层具有较优的抗高温氧化防护性能。为了深入分析其防护机理，提出一种基于计算复合材料电阻值的类比模型，计算在本研究中所定义的材料扩散阻值，以实现对该涂层中氧扩散行为的定量分析。采用基于涂层简化模型的该分析方法能够合理解释复合涂层在高温循环氧化过程，Al2O3与YSZ颗粒的质量比越大，其抗氧化性能越好的的实验现象。. 接着研究渗封处理对溶胶-凝胶涂层的结构及其防护性能的影响。使用硝酸盐水溶液对Al2O3/YSZ-Al2O3复合涂层进行化学致密化渗封处理（PCD）。高温循环氧化结果表明，涂层的防护性能随PCD循环处理次数增加而增强，不过经12次PCD循环处理后，提高其抗高温氧化性能的作用效果发生衰减。涂层表面隆起数目、TGO层增厚及涂层附近金属基体发生内氧化的程度也随PCD循环处理次数增加而减小，受PCD的影响规律与对氧化动力学曲线的影响规律一致。采用所提出的基于复合材料电阻计算类比模型深入分析，可揭示PCD对该复合涂层微观结构及氧扩散行为产生影响的作用机制。. 最后研究磷酸盐渗封处理对涂层结构及其防护性能的影响。采用磷酸盐对铝合金阳极氧化膜进行封孔处理以提高其耐蚀防护性能。电化学阻抗谱分析表明，经磷酸盐封孔处理的阳极氧化膜表现出比常规沸水和铈盐封孔处理更佳的耐蚀防护性能。表明磷酸盐是一种可有效提高涂层致密效果的渗封剂材料。