双相共晶高熵合金凝固组织的电场调控及变形机制

Eutectic high entropy alloys with excellent mechanical properties and cast performance are expected to overcome the limitations of industrial application of high entropy alloys, and become the new in-situ composite material with the most industrial application prospects. In order to promote its industrial application, it is significant to optimize the mechanical properties of eutectic high entropy alloys. Meanwhile, for this kind of alloys, the biphasic coordinated deformation mechanism is seldom systematically investigated, as well as the micro-mechanism of microstructure evolution during tensile deformation. Therefore, in this project, we select the as-prepared Al0.9CoFeNi2 dual-phase eutectic high entropy alloy as the research object. Electric field technique (i.e. single direct current field, single alternating current field and single pulse electric field) is introduced in the solidification process to refine the microstructure and improve the mechanical properties of the alloy. The microstructures and mechanical properties of the alloy are investigated by the scanning electron microscopy, transmission electron microscopy, backscattered electron microscopy, nano-indentation, synchrotron radiation in-situ stretching and other experimental techniques. Furthermore, the tensile deformation behaviour of the alloy under room temperature will be also studied. Based on these findings, the relationship of the three factors of manufacturing process-microscopic characteristics-mechanical properties of the materials can be obtained, and the microscopic tensile deformation mechanisms are clarified. This project not only provides a new strategy to optimize the microstructures and mechanical properties of eutectic high entropy alloys, but also lays a theoretical foundation for the industrial application of eutectic high entropy alloys.

共晶高熵合金具有良好力学性能和优异铸造性能，有望突破高熵合金工业化应用所带来的瓶颈，成为最具工业化应用前景的新型原位复合材料。当前，进一步优化共晶高熵合金力学性能是推动其工业化应用所面临的关键问题。同时，该类合金中双相协调变形机制和拉伸变形过程中组织演化及微观机理也缺乏系统研究。本项目以前期制备的Al0.9CoFeNi2双相共晶高熵合金为研究对象，在合金凝固过程中分别引进直流电场、交流电场和脉冲电场以细化合金组织，提高其力学性能，并借助扫描电子显微镜、透射电子显微镜、背散射电子显微技术、纳米压痕、同步辐射原位拉伸等实验技术手段研究该合金组织性能，实现该类材料制备工艺-微观特征-力学性能三要素的微观联系，进而研究该合金室温拉伸变形行为，阐明其变形机制与微观变形机理。本项目的完成不仅为共晶高熵合金组织性能的优化提供一种新途径，也将为共晶高熵合金的工业化应用奠定理论基础。

本项目针对共晶高熵合金力学性能的不足，在双相共晶高熵合金凝固过程中引进电场技术，进一步提升了共晶高熵合金力学性能。研究电场工艺参数对合金微观组织性能的影响规律，探索了合金制备工艺-微观特征-力学性能三要素的微观联系，阐明不同电场施加方式下共晶高熵合金的生长动力学及热力学机制，揭示合金拉伸变形的微观机理及两相协调变形机制。1)考察了电场技术对共晶高熵合金中微观组织以及生长方式的改善，达到了主动控制共晶两相尺寸、形貌及分布的目标，并揭示各种电场作用下共晶形貌的细化机制，阐明合金力学性能与微观组织的关联机制。2)借助准原位拉伸技术，探索了共晶高熵合金在室温拉伸变形过程中滑移系的开动与分布特征以及位错形貌、位错密度、晶体取向演变及微观组织演化，揭示共晶高熵合金拉伸变形的微观机理及两相协调变形机制，研究结果对于指导高性能共晶高熵合金成分设计和形变强化机制具有重要理论研究价值。3)采用真空感应熔炼+脉冲电场技术相结合方式制备了公斤级高熵合金样品，研究了工艺参数对合金组织及性能的影响规律，发现电场条件下制备的共晶高熵合金的强塑性优于大部分已报到道的其他制备方法制备的共晶高熵合金。本项目的研究结果不仅为共晶高熵合金组织性能的优化提供一种新途径，也对共晶高熵合金的工业化应用奠定理论基础。