Nb-Ti-Si基超高温合金表面硅化物防护涂层中B-Y的联合改性作用研究

As a new generation of ultrahigh temperature structural materials, Nb-Ti-Si based ultrahigh temerature alloys have great potential as alternative materials to Ni-based superalloys. However, a major barrier to the high temperature applications of the Nb-Ti-Si based alloys is their poor oxidation resistance. Up to now, many studies have been carried out to develop oxidation resistant coatings for these alloys in the world. However, there have been fewer reports on the preparation of B-Y co-modified silicide coatings on an Nb-Ti-Si based alloys in the open literature. Moreover, the interaction mechanism among the co-modified elements still needs to be studied. The project is intended to study the Si-B-Y coatings on an Nb-Ti-Si based ultrahigh temerature prepared by one step pack cemenetation and/or pack cemenetation-molten salt method. The aims are to fully use the reactive element effect of rare element Y and B element to improve the compactness and toughness of the silicide coatings, and thus to improve the compact and adhesion of the scale after oxidation or hot corrosion. Through the optimization of process conditions, compact and uniform B-Y co-modified silicide coatings with the most optimal component and structure can be achieved, which also show metallurgical bonding with the substrate. It is also focused on studing the synergic effect of B and Y on the structure formation, growth kinetics, oxidation kinetics, hot corrosion kinetics and scale formation of the silicide coatings. The results obtained can provide the theory basis for the preparation and modification of high temperature coatings, and also will be used as scientific basis for further research and development of the high temperature oxidation coatings of refractory alloys.

Nb-Ti-Si基超高温合金作为新一代超高温结构材料，有望取代镍基单晶合金。但该合金在高温下较差的抗氧化性能成为制约其应用的主要瓶颈之一。目前国内外针对该合金关于B，Y联合改性硅化物涂层的研究尚未见系统的文献报道，而且多元改性元素之间的相互作用机理有待研究。本项目拟分别采用一步扩散渗和两步扩散渗-熔盐法在新型Nb-Ti-Si基超高温合金表面制备Si-B-Y多元渗层，目标是充分利用稀土Y及B元素的活性效应，提高涂层的致密性和韧性，以改善氧化膜的致密性和粘附性。通过对制备工艺条件的优化设计，制备出成分可控、结构可控、厚度均匀、致密、与基体冶金结合的Si-B-Y多元共渗涂层。研究B，Y元素对硅化物涂层组织形成、生长动力学、氧化动力学、热腐蚀动力学及氧化膜形成的协同作用效应。研究结果为高温涂层制备及改性优化提供理论依据，为进一步研究和开发难熔金属超高温抗氧化涂层提供科学依据。

Nb-Ti-Si基超高温合金被认为是替代Ni基高温合金的新型先进高温结构材料之一。本项目针对Nb-Ti-Si基超高温合金表面硅化物涂层脆性大、氧化膜流动性差等问题，利用稀土Y及活性元素B的改性作用，制备了Si-B-Y多元涂层，探明涂层的组织形成机理及生长动力学规律，同时阐明了涂层的氧化膜及热腐蚀膜的形成规律及其动力学特征，为开发耐高温、长寿命高温涂层及其制备技术提供了理论和技术支撑。主要研究结果如下：1) 优化了一步法Si-B-Y共渗涂层的制备工艺参数，揭示了Si、B及Y的渗入机制，发现B优先在硅化物上沉积，在涂层中主要以NbB2相的形式存在，Y则主要固溶在涂层中；2) 探明了两步法制备的多元共渗层的组织特征、成分分布及界面特性，B化过程易于在Si-Y共渗硅化物涂层上形成NbB2相，而Si-Y共渗则对B化层的厚度影响不大；3) 通过B和Y联合改性，氧化膜的流动性和粘附性得到了明显改善，在1250 ℃可至少有效防护合金100 h，氧化膜的主要组成相为TiO2，SiO2和Cr2O3；4) 评价了Si-B-Y多元渗层在900 ℃的抗热腐蚀性能，获得了热腐蚀动力学规律，探讨了热腐蚀过程中硅化物涂层的破坏规律，腐蚀产物膜的主要组成为TiO2、NaNbO3及无定形硅酸盐的混合物。本项目相关研究结果发表学术论文5篇，其中SCI收录4篇，获授权发明专利1项。