2024-T3铝合金表面磁控溅射沉积氧化铈基涂层的制备及耐腐蚀性能研究

发布时间：2018-06-21 02:19

  本文选题：氧化铈 + 涂层　； 参考：《重庆大学》2016年博士论文

【摘要】：金属材料的腐蚀与防护一直是航空航天、汽车等工业领域的研究热点。国内外大量研究集中于采用表面涂层工艺增强铝合金的耐腐蚀性能。其中,铝合金表面沉积铬基涂层是过去80年里在航空航天和汽车工业领域应用最广泛的、耐腐蚀效果最好的、研究最透彻的涂层工艺。但近年来,六价铬化合物因具有剧毒性和致癌性而被限制使用,此后,国内外大量的研究集中于铬膜替代物的研究与开发。其中稀土转化膜,特别是铈基转化膜,是去铬化涂层中给铝合金提供腐蚀保护效果最好的涂层体系。然而,现有的关于铝合金表面铈基防腐涂层的研究都是采用基于液相反应的化学法来沉积铈基涂层,这些化学方法的制备过程都涉及铈基化合物及其他酸性或碱性溶液的使用和废弃,对环境有较大的影响。采用化学法制备的氧化铈基涂层存在较多微米级尺度的裂纹及缺陷,且与铝合金基体的结合力不佳。此外,由于现有的基于液相反应的制备工艺不能控制氧化铈基涂层的化学组成,特别是其中Ce基团的价态,至今铈基涂层覆盖的铝合金基材对腐蚀介质的响应机制未能得到透彻的研究。因此,采用绿色环保的制备工艺,改善铈基涂层的表面形貌和膜基结合强度,深入探讨涂层中Ce基团的价态、涂层的微观结构与腐蚀性能间的关系,对铈基涂层在高强铝合金防腐领域的推广应用具有重要意义,也能为铈基防腐涂层在其他金属腐蚀保护领域的应用带来一定的启发。本文采用磁控溅射技术在Al 2024-T3合金表面沉积了CeO_2涂层,研究了的涂层的厚度、表面形貌、晶型结构、膜基结合强度及电化学腐蚀性能,并分析比较了磁控溅射法制备的CeO_2涂层与化学法所制氧化铈基涂层在形貌、结构和腐蚀特性上的异同。实验结果表明,与化学法制备的氧化铈基膜层相比,磁控溅射沉积的CeO_2涂层为Al合金基材提供了效果相当或更佳的阴极抑制效应,且具有更少的表面缺陷和更高的膜基结合强度,可以为2024-T3铝合金基材提供较好的腐蚀保护。然而,本实验条件下制备的CeO_2涂层并不具备磷化后期处理的氧化铈转化涂层所具有的动态电化学活性,只能充当腐蚀介质和铝合金基体间的静态物理阻隔层。采用共溅射法在CeO_2涂层的沉积过程中引入Al原子制备了Ce-Al-O涂层,分析比较了铝合金基材表面沉积的Al、CeO_2和Ce-Al-O三种涂层的晶体结构、微观结构、化学组成及电化学腐蚀特性的异同,结果表明2024-T3铝合金表面沉积的Al涂层为三维岛状晶态结构,CeO_2涂层为柱状晶态结构,二者均是作为腐蚀介质和铝合金基体间的物理阻隔层来为铝合金基体提供一定的腐蚀保护,对Al合金基体的点蚀特性无改善。而对于Ce-Al-O涂层,Al原子在沉积过程中的引入使得柱状晶态CeO_2结构转变为致密均匀的非晶或超细纳米晶Ce-Al-O结构,使纯Al 2024-T3合金基材的耐腐蚀性能提高三个多数量级,并大幅降低了铝合金基体发生点蚀破坏的倾向。通过改变CeO_2靶材的功率,研究了Ce-Al-O涂层化学组成的改变对膜基体系电化学腐蚀性能的影响;并在保持Ce-Al-O涂层化学组成不变的条件下,研究了Ce-Al-O涂层的厚度对Ce-Al-O涂层的微观结构和耐腐蚀性能的影响。结果表明,Ce-Al-O涂层厚度的改变不会改变涂层在电化学测试中的动态腐蚀响应特性的本质,但Ce-Al-O涂层对铝合金基体的电化学腐蚀过程的抑制效果,特别是对铝合金基体阳极点蚀过程的改善取决于涂层对样品的有效覆盖、涂层内致密层厚度、及Ce(III)基团的比例和含量。通过长期盐浴浸泡实验研究了Al 2024-T3合金基材表面磁控溅射沉积的CeO_2和Ce-Al-O涂层的长期腐蚀响应,提出了CeO_2和Ce-Al-O涂层对基材不同的腐蚀保护机制。当涂层内的Ce基团主要以Ce(IV)形式存在时,晶态CeO_2涂层具有很好的化学惰性,是铝合金基体和腐蚀介质间优异的阻隔层,涂层完好的情况下能为铝合金基体提供良好的腐蚀保护,但破损的涂层不具备自修复能力;当涂层内的Ce基团主要以Ce(III)形式存在时,所沉积的非晶态Ce-Al-O涂层具有致密的微观结构和良好的膜基结合强度,在腐蚀过程中基于Ce、Al、O原子间的氧化还原反应和Ce离子的选择性释放而实现对腐蚀介质的动态响应,涂层在一定程度上具有自修复的特性。
[Abstract]:Corrosion and protection of metal materials have been a hot spot in aerospace, automotive and other industrial fields. A large number of studies have focused on the corrosion resistance of aluminum alloys with surface coating technology. The chromium based coating on the surface of aluminum alloy is the most widely used in the field of aerospace and automobile industry in the past 80 years. The best effect is to study the most thorough coating process. However, in recent years, six valence chromium compounds have been limited to use because of their highly toxic and carcinogenicity. After that, a large number of studies at home and abroad have focused on the research and development of chromium film substitutes. However, the existing research on the cerium based anticorrosive coating on the aluminum alloy surface is to use the chemical method based on liquid phase reaction to deposit cerium based coating. The preparation process of these chemical methods involves the use and discarding of cerium based compounds and other acidic or alkaline solutions, which has a great influence on the environment. The cerium oxide based coating prepared by the method has many micron scale cracks and defects, and the bonding force to the aluminum alloy matrix is not good. In addition, the chemical composition of the cerium oxide based coating can not be controlled by the existing preparation process based on the liquid phase reaction, especially the valence state of the Ce group, so far the aluminum alloy substrate covered by the cerium base coating is so far. The response mechanism of the corrosive medium has not been thoroughly studied. Therefore, the green and environmental preparation technology is adopted to improve the surface morphology and bond strength of the cerium based coating. The valence state of the Ce group in the coating, the relationship between the microstructure and corrosion properties of the coating are discussed, and the application of the cerium based coating in the field of high strength aluminum alloy anticorrosion is applied. It is of great significance and can enlighten the application of cerium based anticorrosion coating in the field of other metal corrosion protection. In this paper, the CeO_2 coating was deposited on the surface of Al 2024-T3 alloy by magnetron sputtering. The thickness, surface morphology, crystal structure, bond strength and electrochemical corrosion properties of the coating were studied and compared. The morphology, structure and corrosion characteristics of the CeO_2 coating prepared by the magnetron sputtering and the cerium oxide based coating made by chemical method are different. The experimental results show that the CeO_2 coating deposited by magnetron sputtering provides a better or better cathodic inhibition effect for Al alloy substrate than the cerium oxide base film prepared by chemical method. The surface defects and higher bond strength can provide better corrosion protection for the 2024-T3 aluminum alloy substrate. However, the CeO_2 coating prepared under this experimental condition does not possess the dynamic electrochemical activity of the cerium oxide conversion coating treated by the later phosphating process, only as the static physics between the corrosion medium and the aluminum alloy matrix. The Ce-Al-O coating was prepared by Al atom in the deposition process of CeO_2 coating by CO sputtering. The crystal structure, microstructure, chemical composition and electrochemical corrosion characteristics of the three coatings deposited on the surface of aluminum alloy substrate were analyzed and compared. The results showed the Al coating deposited on the surface of 2024-T3 aluminum alloy. For the three-dimensional Island crystalline structure, the CeO_2 coating is a columnar crystalline structure. The two are both as the physical barrier between the corrosion medium and the aluminum alloy matrix to provide certain corrosion protection for the aluminum alloy matrix, and the pitting characteristics of the Al alloy matrix are not improved. For the Ce-Al-O coating, the introduction of Al atoms in the deposition process makes the columnar crystalline state Ce. The structure of O_2 is transformed into a compact and uniform amorphous or ultrafine nanocrystalline Ce-Al-O structure. The corrosion resistance of the pure Al 2024-T3 alloy substrate is increased by three orders of magnitude, and the pitting damage tendency of the aluminum alloy matrix is greatly reduced. By changing the power of the CeO_2 target, the change of the chemical composition of the Ce-Al-O coating on the membrane based system electricity is studied. The influence of chemical corrosion properties and the influence of the thickness of the Ce-Al-O coating on the microstructure and corrosion resistance of the Ce-Al-O coating on the condition of keeping the chemical composition of the Ce-Al-O coating unchanged. The results show that the change of the thickness of the Ce-Al-O coating will not change the nature of the dynamic corrosion response characteristic of the coating in the electrochemical test, but Ce-Al The inhibition effect of -O coating on the electrochemical corrosion process of aluminum alloy matrix, especially the improvement of the corrosion process of the aluminum alloy matrix anode depends on the effective coverage of the coating to the sample, the thickness of the coating in the coating and the proportion and content of the Ce (III) group. The magnetron sputtering on the substrate surface of the Al 2024-T3 alloy substrate was studied by a long-term salt bath immersion test. The long-term corrosion response of the deposited CeO_2 and Ce-Al-O coatings shows that the corrosion protection mechanism of the CeO_2 and Ce-Al-O coatings on the substrate is different. When the Ce group in the coating mainly exists in the form of Ce (IV), the crystalline CeO_2 coating has good chemical inertness. It is an excellent barrier layer between the aluminum alloy and the corrosion medium, and the coating is in good condition. It can provide good corrosion protection for the aluminum alloy substrate, but the damaged coating does not have self repairing ability. When the Ce group in the coating mainly exists in the form of Ce (III), the amorphous Ce-Al-O coating deposited in the coating has a compact microstructure and good bonding strength of the membrane base. In the corrosion process, the redox reaction between the Ce, Al, and O atoms is based on the corrosion process. The dynamic response of corrosive medium should be achieved with the selective release of Ce ions.
【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG174.4

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