氧化铝-硅酸二钙自封孔涂层的组织结构演化机制及其防腐性能研究

Due to the outstanding anti-wear and anti-corrosion characteristics of oxide ceramics, the corresponding coatings can improve the surface properties of metal material effectively. However, the defects in coatings allow corrosive elements to reach the substrate in marine environment, which leads to the spallation of coatings, the degradation and eventual failure of components. The development of ceramic coatings that are dense enough to prevent the corrosive substance from penetrating into the coating is of great significance to improve the reliability and durability of marine equipments. In this project, alumina-dicalcium silicate coatings with various compositions will be prepared by air plasma spraying (APS). The coatings are able to seal the defects via the hydration of dicalcium silicate, resulting in lowering permeability. The microstructure evolution of coatings in pre-hydration process and three kinds of typical corrosive enviornment (neutral salt spray test, cyclic dry-wet test and brine dipping test) will be investigated systematically. The mechanism and the key influencing factors of self-sealing behavior will be discussed. The relationship between the microstructure with the mechanical properties and corrosion-resistant performance will also be studied, together with the failure mechanisms of the anti-corrosive coatings. This study will provide new clew for improving the corrosion protection capability of plasma sprayed oxide ceramic coatings and promote the development of multifunctionality and practicalization of ceramic coatings.

氧化物陶瓷具有耐磨损、抗腐蚀等特点，作为涂层材料能够有效强化金属材料表面性能。但在海洋环境下，腐蚀介质易通过涂层中的孔隙等缺陷渗透到金属基体，对其造成腐蚀，导致涂层的剥落，最终引发装备故障和失效。封闭涂层中的腐蚀通道对提高海洋装备的可靠性和服役寿命有着重要的意义。本项目拟采用大气等离子体喷涂方法在金属基材上制备氧化铝-硅酸二钙陶瓷涂层。利用硅酸二钙材料的水化特性实现涂层的自封孔，从而增强其防腐蚀性能。将系统研究不同配比氧化铝-硅酸二钙涂层在预水化过程和三种典型腐蚀环境下（中性盐雾、干湿交变、盐水浸泡）组织结构的演化规律，分析涂层发生的物理化学反应，深入探讨涂层自封孔机理及其关键影响因素。建立涂层组织结构与力学性能和防腐蚀性能之间的关联性，明晰涂层防腐失效机理。本项研究可以为提高氧化物陶瓷涂层在苛刻海洋工况下的防腐蚀能力提供借鉴性思路和方法，促进陶瓷涂层的多功能化和实用化发展。

等离子体喷涂陶瓷涂层中的孔隙是海洋环境下腐蚀介质的渗入通道，是涂层防腐失效的主要原因之一。本项目利用Ca2SiO4的水化作用进行涂层自封孔，制备了Al2O3-Ca2SiO4复合涂层、Ca2SiO4涂层和Al2O3参比涂层，研究了Ca2SiO4含量对涂层物相、显微结构、防腐蚀和力学性能等的影响。分析了涂层在去离子水浸泡、盐水浸泡、人工海水浸泡、干湿交替盐雾腐蚀条件下的组织结构与性能演化，揭示了涂层的自封孔机理及关键影响因素。取得的主要研究成果如下：1.采用等离子喷涂技术制备了不同Ca2SiO4含量的陶瓷涂层，其中Ca2SiO4均为具有水化活性的β相。少量Ca2SiO4的引入可以提升涂层的防腐蚀性能。2.去离子水浸泡后，由于Ca2SiO4的水化以及与溶解在水中的CO2的反应，Al2O3-Ca2SiO4复合涂层表面生成CaCO3。涂层中的部分孔隙被填充，展现出自封孔特性。浸泡初期复合涂层的致密化导致涂层显微硬度增大，绝缘性能提高。3.由于溶液中Ca2+浓度和pH值变化，在3.5wt% NaCl溶液中浸泡不同时间后，Ca2SiO4涂层表面生成了不同形貌和晶型的CaCO3。Ca2SiO4涂层在盐水中也具有自封孔效应。宏观形貌、极化曲线、阻抗谱的结果表明，Ca2SiO4涂层在盐水环境中可以长时间保护基材不被腐蚀，与Al2O3涂层相比具有更好的长期防腐蚀性能。4.Ca2SiO4涂层在人工海水中浸泡后，涂层表面形成了海胆状文石。次表层中除了Ca、O，还含有较多的Si和Mg。次表层下仍为Ca2SiO4层，涂层中的内部孔隙被填充。海水中的Mg2+对CaCO3具有晶型控制作用。Ca2SiO4涂层在浸泡之后，涂层的防腐蚀性能提高，而Al2O3涂层浸泡之后，涂层的防腐蚀性能下降。在人工海水中Ca2SiO4涂层的长期防腐蚀性能优于Al2O3涂层。5.Ca2SiO4涂层在42天的干湿交替盐雾试验后，涂层表面未见锈斑。而Al2O3涂层在试验的第4天，涂层表面出现了锈斑，随着盐雾试验的进行，锈斑增大，数量增多。本项目的开展为提高陶瓷涂层在海洋工况下的防腐蚀性能提供了新的思路和方法，为防腐蚀涂层材料的设计和应用提供理论基础和实验数据。