FCC/B2类共晶高熵合金相界面的结构特征及性质研究

The eutectic high entropy alloys with a mixture structure of FCC and B2, which can balance the strength and ductility, are a kind of situ composites with excellent mechanical and casting performance and have important theoretical research values and industrial application prospects. In this project, the high strength and high plasticity Al-Co-Cr-Fe-Ni and Al-Cr-Fe-Ni alloy systems with FCC + B2 eutectic structures will be selected as the research object. Starting from the characteristic of phase boundary, on the basis of high resolution transmission electron microscopy (HTEM) and in-situ tensile testing machine with scanning electron microscopy analysis methods reveal the coordination deformation mechanism of FCC and B2 phases, the fine-structures and the migration mechanism of phase boundary (such as atomic stacking, element distribution, defects and transition layer, etc.), the interaction mechanism between the dislocation and the phase boundary, and the relationship between phase boundary and mechanical properties, in the as-cast, deformation, and heat treatment states. Then, we will build out the atomic structure model of phase boundary, atomic mismatch stress field model in phase boundary, and the interaction model between the phase boundary and the dislocation, eventually reveal the optimization of microstructure and mechanical properties by the control of phase boundary. The accomplishment of this project not only complements the theoretical knowledge of the related phase boundary of FCC + B2 eutectic high entropy alloy, but also provides a theoretical basis for the study of other dual-phase high entropy alloys.

具有FCC+B2混合结构的共晶高熵合金平衡了强度与塑性这对矛盾体，是一类性能优异的原位复合材料，且拥有优异的铸造性能，具有重大的理论研究价值与工业应用潜力。本项目选用具有FCC+B2结构的共晶Al-Co-Cr-Fe-Ni及Al-Cr-Fe-Ni合金系为基础研究对象，从相界面特征入手，借助高分辨透射电镜及带扫描电镜的原位拉伸试验机研究两种合金系在铸态、塑性变形态、以及热处理态下相界面的精细结构（原子堆垛方式、元素分布、缺陷类型、过渡层等）、迁移机制、位错与相界面的交互反应机制、界面性质与合金宏观性能的耦合关系，建立相界面原子结构模型、相界面原子错配应力场模型和相界面与位错交互模型，最终实现通过异相界面调控来优化合金的组织与性能。本项目的完成不仅补充了FCC+B2类共晶高熵合金相关相界面理论知识的空白，也为其它复相高熵合金的研究提供了思路与理论基础。

具有FCC+B2混合结构的共晶高熵合金平衡了强度与塑性这对矛盾体，是一类性能优异的原位复合材料，且拥有优异的铸造性能，具有重大的理论研究价值与工业应用潜力。本项目的实施通过优化铸造工艺、成分设计模型建立、界面组织调控、微合金化、相界面结构设计、热处理及变形机制工艺调控等手段成功地制备并设计出多种具有高性能FCC/B2共晶高熵合金。首先，通过对共晶高熵合金元素间相互关系分析，建立了高效简单的成分设计模型，设计出大量的FCC/B2类共晶高熵合金成分。其次通过XRD、SEM、TEM等方法精确表征了FCC/B2类Al-Co-Cr-Fe-Ni合金中铸态、热处理态、变形态的微观组织转变及相界面的结构特征并对界面中位错滑移机制进行了表征；然后，通过原位拉伸实验及原位弯曲试验，揭示了Al-Cr-Fe-Ni及Al-Co-Cr-Fe-Ni系近共晶高熵合金中FCC与B2两相的协同变形机制及裂纹扩展机制；最后，通过微合金化、原位界面扩散、热处理及变形工艺的研究，探究了FCC与B2两相中及两相界面的演化机制，进一步提升了近共晶高熵合金的力学性能。本项目的研究成果不仅补充了FCC+B2类共晶高熵合金相关相界面理论知识、变形机制、成分设计的空白，也为其它复相高熵合金的研究提供了思路与理论基础。