定向凝固Ni-Co-Cr-Al-W系单晶高熵高温合金的组织调控与强化机理

High entropy superalloys (HESAs) are prototypical concept alloys recently proposed based on the idea of high entropy effect. It is believed that HESAs possess superior high temperature strength, hot corrosion resistance and high temperature creep resistance properties to some of superalloys. So far as present, however, the composition design, structural controlling and high temperature strengthening mechanism of HESAs have been hardly concerned. This program is aimed to deeply investigate the scientific issues of NiCoCrAlW based HESAs, including (1) the phase equilibrium and lattice mismatch between FCC and L12 phase; (2) the solid/liquid interface morphologies and microstructural evolution during the single crystal directional solidification process; (3) the phase stability of L12, TCP phase, carbides and borides and microstructural evolution during the artificial aging and long-time thermal exposure process; (4) the deformation and strengthening mechanism under the coupled thermo-stress condition etc. Through this program, the intrinsic relation among composition, solidification process, artificial aging and high temperature creep properties will be established. This work is hopefully to provide theoretical basis and technological guidance for the application of HESAs for the hot components of aero-turbine and ground internal combustion turbines, and to be beneficial to the development of new type of high temperature structural materials.

高熵高温合金（HESAs）是最近基于高熵效应理念提出的原型概念合金，其高温强度、抗热腐蚀与抗蠕变等性能有望超越某些现有高温合金，而成为航空发动机和地面燃气轮机热端部件用新型高温结构材料。但目前关于HESAs成分设计、组织调控及高温强化机理还近乎空白。本项目拟以Ni-Co-Cr-Al-W系合金为对象，利用Bridgman单晶定向凝固方法，通过相图热力学与第一性原理计算，针对HESAs中FCC/L12相平衡与晶格错配度的精确调控、单晶定向凝固过程中固/液界面形态与组织演变、时效处理和长时热暴露过程中L12相、TCP相和碳硼化合物相的稳定性和组织演化、热力耦合条件下单晶HESAs变形与强化机制等科学问题开展深入研究，建立HESAs成分体系-凝固控制-时效处理-高温蠕变性能之间的内在联系。从而为HESAs在航空发动机和地面燃气轮机热端部件中的应用提供理论和技术依据，推动新型高温结构材料的发展。

高熵高温合金（HESAs）在高温强度、抗热腐蚀与抗蠕变等性能方面有望超越某些现有高温合金，具有成为航空发动机和重型燃气轮机热端部件用新型高温结构材料的发展潜力。本项目以Ni-Co-Cr-Al-W系等合金为对象，采用相图热力学计算方法，系统开展了高熵合金中的FCC/L12相平衡调控和强化机制研究，成功开发了新型Ni-Co-Cr-Al-W系高熵高温合金。通过优化Bridgman法定向凝固工艺参数，成功制备出取向偏离度小的单晶高熵高温合金。开展了合金的固溶和时效处理制度探索，并分析了相组成和组织演变规律，获得了优化的显微组织，使该体系合金具有较高的γ′相体积分数和合适的尺寸。研究表明，新型Ni-Co-Cr-Al-W系单晶高熵高温合金在800°C以上的高温拉伸强度超过MarM247镍基高温合金。蠕变性能测试和组织演变研究表明，蠕变变形过程中γ通道产生大量位错并在γ/γ′界面聚集，大量超位错切割γ′相是合金失效的主要原因。新型Ni-Co-Cr-Al-W系单晶高熵高温合金的承温能力与第一代镍基单晶高温合金相当。此外，项目组还开发了Ni-Co-Cr-Fe-Re和Ni-Co-Cr-Fe-W-Mo系高熵高温合金，研究了这两种合金体系的室温和高温力学性能，揭示了固溶强化和析出强化是其主要强化机制。总之，本项目研究建立了高熵高温合金成分体系、相组成、定向凝固与热处理工艺、高温力学性能之间的关系，为高熵高温合金在航空发动机和地面燃气轮机热端部件中的应用提供了理论和技术依据，对推动新型高温结构材料的发展具有重要意义。