铌硅系超高温材料的稀土改性探索研究

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.

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。

本课题以未来用于1200℃以上的铌硅基超高温结构材料为研究对象，只在通过添加稀土元素改善合金性能。课题通过计算研究了多种稀土元素对铌固熔体和α-Nb5Si3的影响，结果表明Sc、Y、La、Ce、Nd在很大程度上能够提高固溶体的韧性；同时研究了添加Tb、Sm、La、C以未来e、Y添加对铌硅合金微观组织、力学性能、氧化行为的影响，结果表明添加稀土元素后合金的相组成和显微组织没有发生明显的变化，但La和Sm的添加有助于提高铌硅材料的室温断裂韧性；合金的氧化行为也没有发生本质的改变，依然出现了严重的内氧化现象。