铌基超高温合金表面B,Y改性MoSi2涂层的组织形成及抗氧化性能

Advanced Nb-based ultrahigh temperature alloys are prospective candidates for high-temperature structural applications at temperatrues of 1200-1400℃. However, a protective coating is necessary for their high-temperature applications in oxidizing environments. ..MoSi2 coating has excellent oxidation resistance at temperatures above 1000℃, but it suffers "pest" oxidation at 400-600℃ and has poor oxidation resistance at the temperatures below 1000℃. In order to overcome these two defects of MoSi2 coating, we propose to develop B and Y modified MoSi2 coating. B can arrest the "pest" oxidation of MoSi2 and improve its oxidation resistance at the temperatures below 1000℃, and Y can also promote the oxidation resistance of MoSi2. Double glow plasma deposition and halide-activated pack cementation (HAPC) techniques are employeed to prepare B and Y modified MoSi2 coating...Based on the analyses of coating structure and coating formation process, an technical method of preparing dense and controllable B and Y modified MoSi2 coating would be established, and the formation mechanism of Mo-Si-B compound phases during coating deposition process would be revealed. Furthermore, based on the oxidation behavior of B and Y modified MoSi2 coating, the effects of B and Y elements on the "pest" oxidation, scale structure, oxidation resistance of the coating and the interdiffusion between the coating and the substrate would be clarified.

新型铌基超高温合金有潜力在1200-1400℃作为高温结构材料使用，应用前景广阔。研制铌基超高温合金表面高温防护涂层，是推进其走向实用的关键课题之一。本项目以研制铌基超高温合金表面抗氧化性能优异的高温防护涂层为目的，提出研究B, Y改性的MoSi2涂层。利用双辉离子渗和包埋渗相结合的方法，制备组织致密、界面结合力强、结构可控的B, Y改性MoSi2涂层。采用实验和理论分析相结合的方法，系统地研究B, Y改性MoSi2涂层的制备技术、组织形成规律和抗氧化性能，揭示涂层形成过程中Mo-Si-B化合物相的形成机制，阐明元素B和Y对MoSi2涂层低温"pest"氧化、氧化膜结构、高低温抗氧化性能、以及涂层与基体间互扩散的影响，为在铌基超高温合金表面制备抗氧化性能优异的改性MoSi2涂层提供实验和理论依据。

本项目建立了辉光离子渗结合包埋渗法在铌基超高温合金表面制备B,Y改性MoSi2涂层的技术方法，即首先在合金表面制备辉光离子渗Mo沉积层，然后再包埋Si-B-Y/Y2O3共渗制备B,Y改性的MoSi2涂层。1100℃下辉光离子渗Mo可形成与基体扩散结合的Mo沉积层。包埋Si-B-Y/Y2O3共渗过程中，所形成涂层以MoSi2相为主，B在MoSi2外层中过饱和后会析出MoB弥散相，同时B会与Mo反应形成MoB或MoB2内层，所形成的Mo-B化合物内层有抑制Si与基体互扩散的作用，降低了MoSi2退化速度3个数量级；渗剂中B含量对涂层结构影响小，但Y/Y2O3的加入会促进涂层的生长，同时在涂层中渗入约0.2at.%的Ｙ元素。铌基超高温合金表面B,Y改性MoSi2涂层600℃下氧化不发生pest氧化，1250℃下可经受恒温50h和26次1h的循环氧化，高温氧化失效主要是由于涂层中Mo-Si化合物层和Nb-Si化合物层界面开裂所致；涂层中的B氧化时会在表面形成B2O3，有助于氧化膜中缺陷的愈合，涂层中的Y能进一步降低氧化增重约42%。