可内生氧化物扩散障铝化物涂层体系的制备及机理研究

So far, the diffusion barriers developed for the high-temperature protection coating/metallic substrate systems are usually metallic based coatings and ceramic based coatings. Unfortunately, the ceramic diffusion barrier coatings with better performance are rarely used in the system of the metal substrate covered with a diffusion aluminide coating because of the technical limits. In this work, the oxide-dispersed diffusion aluminide coating systems are prepared by partially aluminzing electrodeposited oxide-dispersed Ni films. Unlike the existing work, the deliberately-designed coating system itself forms an oxide rich diffusion barrier at the aluminide/Ni interface by the accumulation of the oxide particles. Simple process, low costs and easy industrialization are the characteristics of this oxide diffusion barrier. The oxide particles of different nature, size and content will be dispersed in the aluminide coating system. The characterization of the evolution of the microstructure and phase compositions with time will be investigated during the vaccum annealing. Using the high resolution transmission electron microscope (HRTEM), the interfacial microstructure of the oxide particles/Ni film and the oxide particles/aluminide coating/Ni film will be characterized. Accordingly, the mechanism for the self-formation of the oxide-rich layer at the degradation front of the aluminide coating will be revealed and a prediction model for the effectiveness of the self-formed oxide diffusion barrier will be established. The result will be helpful for the design, development and application of the novel aluminide coatings with an excellent resistance to the aluminide degradation by the interdiffusion with the metal substrates.

目前，用于阻碍高温防护涂层和基体之间互扩散的扩散障主要分两种，金属基扩散障和陶瓷基扩散障。由于工艺上的限制，性能较优越的陶瓷基扩散障极少被应用于扩散铝化物涂层/合金体系。本项目通过“复合电镀+低温渗铝”两步法在基体上制备氧化物掺杂的铝化物涂层体系。与现有工作不同，该涂层体系中掺杂的氧化物颗粒可自发在铝化物涂层退化前沿聚集，从而形成氧化物扩散障。该扩散障具有工艺简单、成本低、易于工业化应用等优势。本研究将制备不同种类、粒度及含量氧化物掺杂的铝化物涂层体系。对比研究它们因真空退火所导致的微观结构、成分的变化，同时利用高分辨透射电镜（HRTEM）等手段观测氧化物颗粒/Ni镀层和氧化物颗粒/铝化物涂层/Ni镀层的界面结构特征，揭示铝化物涂层退化前沿内生氧化物扩散障的微观机制，建立氧化物扩散障有效性的预测模型。本研究将为抗退化性能优异的高温防护涂层的设计、开发和应用奠定基础。

本项目通过“复合电镀+低温渗铝”两步法在基体上制备了不同含量、尺寸及种类氧化物掺杂的铝化物涂层体系。对比研究以上铝化物涂层因真空退火所导致的微观结构、成分的变化，发现纳米CeO2和Al2O3颗粒的添加均可有效减轻δ-Ni2Al3/Ni涂层体系的退化；随着CeO2颗粒含量的增加（CeO2含量为1-3wt.%），其对互扩散的抑制作用明显增强；微米CeO2颗粒的添加对涂层和基体的互扩散几乎没有影响。同时，研究了δ-Ni2Al3/Ni涂层体系剩余镀层厚度对涂层和基体互扩散行为的影响，发现在镀层氧化物颗粒含量一定的情况下，渗铝后剩余镀层厚度（本质上是弥散氧化物颗粒的数目）是影响扩散障有效性的重要因素。由此分析了氧化物颗粒影响铝化物涂层退化前沿氧化物扩散障形成的本征因素，进一步完善了揭示氧化物扩散障内生机制的“界面拖曳模型”。基于以上实验结果，通过复合电沉积在纯镍表面制备了外层CeO2颗粒含量为1wt.%，内层CeO2颗粒含量为3wt.%的梯度Ni-CeO2镀层，然后对复合镀层低温渗铝，制备了一种新型纳米CeO2改性铝化物梯度涂层。对CeO2改性铝化物涂层的高温氧化性能进行研究，发现CeO2颗粒的加入可以推迟一层完整α-Al2O3膜的形成时间，降低氧化膜的生长速率，同时提高氧化膜的粘附性能。因此，该梯度涂层既具有较好的抗氧化性能，又可在高温过程中内生氧化物扩散障，有效阻碍涂层和基体的互扩散。除此之外，本研究在晶界迁移理论和相关实验结果的基础上，初步建立氧化物扩散障有效性的预测模型，为可内生氧化物扩散障铝化物涂层在高温防护涂层领域的应用提供理论和实验基础。