抑制钛合金缝隙腐蚀性能的探索-表面梯度纳米化后离子渗氮

钛合金优异的自钝化耐蚀性使之在海洋工程中有巨大应用前景，通过离子渗氮可进一步提高其耐磨及耐蚀性。但普通渗氮层的致密度及与基体结合力的不足导致渗层的耐蚀性和稳定性不高。另外，深海中的低氧/无氧环境使得钛合金自钝化性能难以发挥作用，而结构缝隙内容易处于高Cl-、低PH值的高活性状态，使之易发生缝隙腐蚀，导致失效甚至灾难性事故。本项目拟在钛合金表面制备梯度纳米晶结构渗氮层来解决其缝隙腐蚀这一关键问题。首先将表面喷丸与离子渗氮工艺相结合在钛合金表层形成梯度纳米晶渗氮层，并掌握纳米化对N原子在不同结构钛合金中的扩散增强作用，实现对渗氮层梯度结构的控制；重点研究梯度纳米晶渗氮层的致密性和与基体结合力及其对缝隙腐蚀的抑制作用和机理，最后综合揭示局部腐蚀和界面结合力对梯度纳米晶渗氮层中裂纹萌生与扩展的协同作用规律和机理，通过表层纳米晶梯度结构实现全面提高钛合金离子渗氮层抗均匀腐蚀、缝隙腐蚀和磨损性能的目的

Titanium alloy has great application prospect in offshore engineering because of its excellent self-passivated corrosion resistance, and its corrosion resistance and wear resistance can be further improved by plasma nitriding. However, the corrosion resistance and stability of the nitrided layer are not high enough due to the relatively low compactness and interfacial adhesion of the ordinary nitrided layer. Furthermore, the self-passivation performance of titanium alloy is difficult to play the role in the low oxygen/anaerobic environment in deep sea and the structure gap is easy to be in a highly active state because of the accumulated high Cl- and low pH value, making crevice corrosion to occur and leading to failure or even catastrophe accidents. This project intends to solve this key problem of crevice corrosion of titanium alloys by preparing plasma nitrided layer with a gradient nanocrystalline microstructure on its surface. Firstly, surface shot peening and plasma nitriding processes are combined to form a gradient nanocrystalline nitrided layer on the surface of titanium alloys, and the effect of nanocrystallization on the diffusion enhancement of N atoms in different structural titanium alloys is focused and well understood so as to realize the control on gradient microstructure of nitrided layer. The compactness and interfacial adhesion of gradient nanocrystalline nitrided layer, especially its inhibition mechanism on crevice corrosion, are mainly investigated. Finally, the synergistic effect and mechanism of local corrosion and interfacial adhesion on crack initiation and propagation in the gradient nanocrystalline nitrided layer are revealed. The goal of fully improving the uniform corrosion resistance, crevice corrosion resistance and wear resistance of the titanium alloys by plasma nitrided layer is expected to be achieved through the surface gradient nanocrystalline microstructure.