本项目以Nb-Si系超高温结构材料为研究载体，探索稀土元素对其组织和性能的影响。采用量子力学第一原理计算方法，计算多种稀土元素在Nb基固溶体和铌基硅化物中的占位倾向以及对合金相晶格结构的影响，分析获得稀土元素对合金相本征性质的影响机制；在此基础上，选择用于Nb-Ti-Si-Cr-Al-Hf多元系材料微合金化的稀土种类，设计、制备含有不同稀土种类和含量的多元材料，研究稀土元素在多元Nb-Si系材料中的存在位置、存在形式以及对其硅化物强化相的形状、尺寸、分布的影响，研究稀土微合金化后Nb-Si系材料在高温下的组织演变，并研究其室/高温力学行为和高温氧化行为，揭示稀土元素对多元Nb-Si系材料的组织演变、强韧化、变形、断裂以及高温氧化行为的影响机制，为发展承温能力在1200-1400℃范围内使用的Nb-Si系超高温结构材料奠定理论基础。

The objective of this proposal is to investigate the influence of rare-earth elements on the microstructures and properties of Nb-Si based ultrahigh temperature structural materials. From first-principles theory in quantum mechanics, the occupying tendencies of kinds of rare-earth-elements atoms in the crystal lattices of Nb based solid solution and Nb silicides will be calculated and the lattices variations will be analyzed, to obtain the effects of rare-earth elements on the intrinsic properties of alloy phases in Nb-Si based materials. Based on the results mentioned above, the kinds of rare-earth elements will be selected as the micro-alloy elements for Nb-Ti-Si-Cr-Al-Hf multi-element materials. The Nb-Si based materials with different kind and content of rare earth (Nb-Si-RE alloy) will be designed and will be prepared by no-consumable arc furnace in vacuum. Through the micro-analysis, the location and the existing state of rare earth in Nb-Si based materials will be detected. The shape, dimension and distribution of Nb-silicides in Nb-Si-RE alloys will also be observed. Furthermore, the microstructure transformation in high temperature, the room/high-temperature mechanical behaviors and the high temperature oxidation behaviors of Nb-Si-RE alloys will be studied. Eventually, the microstructure transformation, strengthening and toughening, deformation, rupture, and oxidation resistance mechanisms of Nb-Si-RE alloy will be achieved, which is the important supports for the development of Nb-Si based ultrahigh temperature structural materials.