非晶金属涂层力学和腐蚀耦合作用机制研究

Fe-based amorphous alloys are provided with high glass-forming ability, enhanced mechanical properties integrated superior corrosion resistaqnce and low cost, however, they are more suitable to the industrial applications for coatings due to the fatal disadvantages of poor toughness. The key factors that affect the failure of the coatings are mechanical load and corrosive environments. The traditional research tends to pay close attention to the performation of amorphous alloys in purely mechanical or purely corrosive environment. Little systematic research has been conducted on the coupling mechanism of amorphous metallic coatings (AMCs) under the mechanics and corrosion. This research is focused on the Fe-based AMCs served in mechanical and corrosive environments.The passivation characteristics of Fe-based AMCs bearing with static stress and dynamic strain are studied by the microscopic in situ electrochemical testing at the interface of coatings and corrosion solutions. Emphasis is placed on the electrochemical heterogeneity of the interface. The effects of mechanical factors (static stress and dynamic strain) on the environment sensitive fracture of AMCs are also investigated. By using the finite element analysis, the internal relations among static stress induced micro-structure inhomogeneity and pitting sensitivity are established. Besides, the dynamics rules of dynamic strain influenced on the crack initiation and propagation are determined. Based on this, the microscopic coupling mechanism of mechanics and corrosion is revealed. Finally, the interactional rules of mechanical factors and corrosion process are discussed, which can provide the theoretical support for the Fe-based AMCs appliced in mechanical and corrosive environments.

铁基非晶合金玻璃形成能力强，集优异的力学性能和耐蚀性于一体，成本低廉，已成为工业界一种极具应用价值的新型材料，但较差的塑韧性使其作为涂层材料更具应用前景。力学和腐蚀是非晶涂层在应用过程中不可避免并导致其失效的关键影响因素，传统研究多倾向于关注非晶合金在纯力学和纯腐蚀条件下的服役行为，目前尚缺少对其在力学和腐蚀耦合环境中作用机制的系统认识。本项目以腐蚀介质中服役铁基非晶涂层为研究对象，从涂层/溶液界面的电化学不均匀性入手，以微电极电化学、原位高分辨测试及有限元分析为手段，系统研究静应力和动应变等力学因素对非晶涂层钝化稳定性和环境敏感断裂行为的影响规律，建立应力诱发钝性材料结构不均匀性与点蚀敏感性内在联系，确定应变速率诱导裂纹萌生及影响扩展的动力学规律，揭示力学和腐蚀耦合作用下涂层的微观作用机制，探讨非晶涂层力学和腐蚀交互作用规律，为非晶涂层在力学和腐蚀耦合环境中的应用奠定理论基础。

本项目系统研究静应力和动应变等因素对非晶涂层钝化稳定性和环境敏感断裂行为的影响规律，揭示力学和腐蚀作用下涂层的微观作用机制。通过研究主要得出以下认识：1.建立了AC-HVAF喷涂工艺与非晶涂层组织、非晶相含量、孔隙率及耐蚀性间的关联性，确定了涂层耐蚀性与腐蚀介质、环境参数等因素的影响规律。2.发现了基于显微维氏硬度计的机械压痕法评价非晶涂层残余应力的方法，建立了残余应力诱发非晶涂层结构不均匀性与点蚀敏感性内在联系。高的残余应力降低了涂层的均匀腐蚀抗力，膜层缺陷浓度增加，点蚀敏感性增加。确定了残余应力影响非晶涂层钝化稳定性的规律。3.揭示了HVAF和HVOF非晶点蚀敏感性规律和冲刷腐蚀机理。HVAF非晶涂层均匀腐蚀阻力高，点蚀萌生机率小，抗局部腐蚀的能力强。高的硬度高使其具有高的抗冲蚀性能。涂层失效主要来自于涂层缺陷部位冲刷带来的机械损伤，冲刷和腐蚀交互作用加速了损伤过程。4.建立了恒载荷、动应变与非晶涂层钝化稳定性间的关联性。恒载荷、温度和Cl-升高恶化了涂层均匀腐蚀阻力和钝化稳定性，pH值影响非晶涂层的敏感断裂过程。动应变时，应变速率影响涂层钝化稳定性与析氢腐蚀过程，随Cl-浓度和动应变速率的增加而降低，但涂层具有良好的抵抗点蚀的能力。5.确立了恒载荷、动应变对非晶涂层环境敏感断裂行为的影响规律。非晶涂层呈现出低的环境敏感断裂阻力，符合典型的阳极溶解机制。不同于恒载荷，动应变裂纹扩展不形成二次裂纹，裂纹无明显分叉。6. 提出了非晶涂层力学和腐蚀耦合作用机制。在涂层缺陷部位优先形成局部腐蚀，应力增加了局部腐蚀的敏感性，促进裂纹萌生和扩展，并加速了Cl-扩散通道。拉应力和腐蚀联合作用下，裂纹穿过未熔颗粒迅速扩展，产生不连续片状断裂。腐蚀与载荷的耦合作用，加剧了涂层的环境敏感断裂过程，非晶涂层具有一定的环境敏感断裂风险。以上研究结果奠定了非晶涂层在力学和腐蚀耦合环境中的应用的理论基础。