高Nb-TiAl合金的晶界偏析行为及其对环境脆性的作用机制

Owing to the outstanding mechanical properties at elevated temperature, TiAl-based intermetallic compounds with low density and high specific strength have attracted attention as strong candidates for high-temperature structural applications in the aircraft, aerospace, nuclear and automotive industries. It has been recognized as the best approach to improve comprehensive mechanical property and increase the service temperature of TiAl-based intermetallic compounds by alloying with high Nb content. Due to the limitations in understanding the mechanism of embrittlement, the environmental embrittlement is still an obstacle for applications at elevated temperature of TiAl-based intermetallic compounds. In this applied project, it is planned to investigate the forming mechanism and migration of the grain boundary segeration in high Nb containing TiAl intermetallic compounds. The present project focuses on the interface reaction of high Nb containing TiAl alloys in various ambient mediums and the related gas atom diffusion behavior within alloys. It is expected to explore the gas atom diffusion mechanism of high Nb containing TiAl alloys about the room-temperature hydrogen embrittlement, oxygen induced embrittlement at evaluated temperature, oxidation behavior and helium induced environmental embrittlement. Role of grain boundary segregation on the environmental embrittlement and the relation between them will be investigated to clear the nature of the environmental embrittlement of high Nb containing TiAl alloys. Based on the above mentioned research, the possible influence mechanism of grain boundary segeration on the environmental embrittlement and the corresponding mechanism of high Nb containing TiAl-based alloys will be proposed. The obtains of the present project will provide fundamental theoretical foundation and technical guidance for the improvement of environmental embrittlement of high Nb containing TiAl-based ordered intermetallic compounds used as structural materials at elevated temperature.

轻质高强TiAl基金属间化合物因其优异的高温力学性能在航空航天、核能及汽车工业等领域的高温部件有着广阔的应用前景。高Nb合金化成为公认的改善TiAl基金属间化合物综合力学性能和提高使用温度的最佳途径，但因缺乏对TiAl基金属间化合物脆性本质的认识，TiAl基金属间化合物的环境脆性迄今仍是其作为高温结构材料应用的重要障碍。本申请项目拟研究高Nb-TiAl合金晶界偏析的形成机制及演化规律，研究环境介质中气体原子在高Nb-TiAl合金扩散行为，掌握高Nb-TiAl合金在环境介质中的界面反应特征，揭示高Nb-TiAl合金的室温环境氢脆、高温氧脆、高温氧化及核能环境中氦脆的气体原子扩散机制，明确晶界偏析对高Nb-TiAl合金环境脆性的影响规律和作用机制，揭示高Nb-TiAl合金在环境介质中的脆性断裂机理以及晶界偏析与环境脆性的关系，为改善TiAl基有序金属间化合物的环境脆性提供理论支持和技术指导。

轻质高强TiAl 基金属间化合物因其优异的高温力学性能在航空航天、核能及汽车工业等领域的高温部件有着广阔的应用前景。高Nb 合金化已成为改善TiAl 基金属间化合物综合力学性能和提高使用温度的有效途径，但因缺乏对TiAl基金属间化合物脆性本质的认识，TiAl 基金属间化合物的环境脆性迄今仍是其作为高温结构材料应用的重要障碍。本项目研究了高Nb-TiAl 合金晶界偏析的形成机制及演化规律，晶界β偏析导致Nb、W、Ti元素富集同时Al贫化是组织中出现成分不均匀的主要原因，Tα温度附近短时保温退火可大幅减少或消除晶界β相并可避免片层团的显著长大；研究氧气、真空、空气和氢气等环境气氛介质中对近片层和全片层组织高Nb-TiAl 合金力学性能和脆性断裂行为，发现不同组织的合金均会受到氢气诱发的氢致环境脆性的影响，其中热处理后的近片层组织具有最好的环境脆性抗力，铸态合金由于存在显著的晶界偏析其氢致环境脆性现象最为显著，经热处理时后的全片层组织对环境的敏感程度介于热处理所得近片层组织和具有显著晶界偏析的铸态近片层组织之间；发现高Nb-TiAl合金的环境脆性对γ相的形貌非常敏感，片层团界处γ相的存在可显著抑制合金中水汽以及氢气诱导的环境脆性过程，而β相对氢致环境脆性具有促进作用，离子注入研究结果表明高Nb-TiAl合金α2相中的氦泡尺寸大于γ相中的氦泡尺寸，全片层组织具有良好的抗离子辐照能力；研究了环境介质中气体原子在高Nb-TiAl 合金扩散行为及界面反应特征，合金中贫Al区域的存在不利于在高温形成连续致密的氧扩散屏障，但Nb的富集能够缓解这一有害作用，氧元素的扩散行为会通过形成氧化产物和固溶强化作用引起环境/基体界面显微硬度的增加；揭示了高Nb-TiAl 合金的室温环境氢脆、高温氧脆、高温氧化及核能环境中氦脆的脆性断裂行为及受控机制，明确了晶界偏析对高Nb-TiAl 合金环境脆性的影响规律，探讨了高Nb-TiAl 合金在环境介质中的脆性断裂机理以及晶界偏析与环境脆性的关系，研究结果可为改善TiAl 基有序金属间化合物的环境脆性提供理论支持和技术指导。