难熔金属硅化物涂层扩散障原位构筑及高温抗氧化机理研究

Silicide coating is currently the main solution to solve the heat/oxygen protection problem of high-temperature structural materials based on refractory metal in aerospace industry. However, with the iterative equipment, increased service temperature and life expectancy, it is urgent to require silicide coating to enhance high temperature oxidation resistance. The excessive diffusion rate of silicon into the substrate and the large consumption are the common problems that restrict the performance improvement. Selecting effective means to obtain slow diffusion of silicon and reveal the mechanism is the key to achieving improved coating performance. The project will use multi-scale calculation simulation, in-situ construction of diffusion barrier and other methods to design refractory metal carbide/boride diffusion barrier, study high temperature diffusion behavior and resistance diffusion mechanism. The interface structure of refractory metal/diffusion barrier/silicide coating and the coupling mechanism will be clarified. The relationship between the diffusion barrier structure and the diffusion resistance ability as well as the diffusion resistance mechanism will be revealed. By constructing the microstructure evolution model and life prediction model of the coatings in ultra-high temperature environment, the influence law of diffusion barrier introduction on the microstructure of silicide coating and its “composition-structure-performance” evolution law will be defined. The implementation of the project will provide experimental basis and theoretical guidance for solving the problems of high-temperature silicon diffusion of refractory metal silicide coating, poor thermal compatibility between coating and substrate, and low ultra-high temperature oxidation resistance.

硅化物涂层是目前解决航天领域难熔金属高温结构材料热/氧防护难题的主要方案，但随着尖端装备迭代、服役温度升高与寿命要求提高，迫切要求提升硅化物涂层的高温抗氧化性能。硅元素向基体扩散速率过快、消耗量大是制约其性能提升的共性难题。选择有效手段实现高温阻硅扩散并理清机制，是实现涂层性能提升的关键。本项目采用多尺度计算模拟、扩散障原位构筑等方法，开展难熔金属碳化物/硼化物扩散障设计与制备、高温扩散行为与高温抗氧化阻扩散机制研究，从超微尺度探明难熔金属/扩散障/硅化物涂层界面结构及其耦合机制，阐明扩散障组织结构与高温阻扩散效能的构效关系及其阻扩散机制，构建超高温环境下涂层各界面微结构演化模型与寿命预测模型，揭示扩散障引入对硅化物涂层组织结构的影响规律及其成分-结构-性能演变规律，为难熔金属硅化物涂层高温硅元素扩散过快、涂层与基体热匹配性不良、高温抗氧化性能偏低等问题的解决提供实验依据与理论指导。

以钼、铌、钽、钨为代表的难熔金属及其合金广泛应用于航天航空与特种工业的热端部件，但由于其高温氧亲和势高，超过600℃就会发生严重氧化，因此以Si-Mo基为代表的硅化物涂层成为难熔金属热/氧防护的重要涂层体系。随着现代工业快速发展，难熔合金部件服役温度与时间持续提高，迫切要求提升涂层高温抗氧化性能，因此耐高温长寿命涂层研制及相关基础共性问题研究是国内外研究热点。高温下涂层中的有益元素Si向难熔金属基体扩散速率过快、消耗量大是制约硅化物涂层性能提升的共性难题。.本项目提出添加扩散障界面层抑制硅元素向基体内扩散的新策略，采用卤化物活化包埋渗法在钼合金、钽合金、铌合金等难熔金属合金表面原位制备了硼化物、碳化物、铝化物三种扩散障，对比研究了不同扩散障与难熔金属合金基体的适配性、阻硅扩散效果及其涂层高温防护性能，发现硼化物为扩散障优选体系。设计制备了含扩散障的复合硅化物梯度涂层，添加了NbB2-Nb3B2硼化物扩散障的Si-Mo-W-ZrB2-YSZ涂层在1850℃服役寿命提升约2.3倍，涂层在1850℃下可有效防护超13h、室温-1850℃热震超600次。.本项目首次探索出适用于钽合金硅化物涂层的扩散障体系，开发了多组元可自修复梯度复合陶瓷涂层及其扩散障原位构筑+料浆烧结/多弧离子镀+复合包渗三步制备技术，从超微尺度探明了基体/界面层/Si-Mo基涂层三者的界面结构耦合机制，借助第一性原理等计算模拟手段剖析了扩散障组织结构与高温阻扩散效能的构效关系及其阻扩散机制，构建了1600℃-1850℃超高温环境下复合硅化物涂层各界面微结构演化模型与寿命预测模型，结合有限元仿真模拟等手段阐释了涂层界面应力模型及其热震失效机制，揭示了扩散障引入对硅化物涂层组织结构的影响规律及其成分-结构-性能演变规律，阐明扩散障功能实现机理，为难熔金属硅化物涂层高温硅元素扩散过快难题提供了全新策略，为难熔金属合金硅化物涂层的超高温、长寿命、耐热震设计与制备提供了理论指导与基础实验数据。