增材制造因其独特的“自下而上”的生产模式，具有缩短研制周期、结构优化设计、节省资源、降低成本的技术特点；高熵合金具有广泛的设计空间，表现出比传统合金更卓越的机械性能。将增材制造与高熵合金相结合，不仅能利用增材制造的技术优势，还能突破高熵合金的性能优势，这种协同作用为开发新时代高性能、高功能先进金属材料指明了道路。尽管增材制造高熵合金前景迷人，其尚处于探索阶段，一系列科学问题有待回答。增材制造高熵合金的微观组织往往具有复杂的结构特征。这种复杂结构特征来源于两个层面：一是增材制造非平衡凝固引起的典型凝固特征；二是高熵合金多组元特性引起的结构异质性。充分理解微观结构与宏观性能之间的关系，是增材制造高熵合金实现高性能所必须面对的挑战。工艺决定结构，结构决定性能。唯有选择合适的工艺进行有效的微结构调控，以实现“形态控制”；才能满意地优化力学性能，以实现“性能保证”。

本文将对增材制造高熵合金进行广泛的微结构调控以及详细的变形机理分析。研究分为两大部分：第一部分以单相高熵合金为研究对象，在不考虑高熵合金结构异质性的前提下，对增材制造引起的凝固特征（残余应力和柱状晶）进行针对性的后处理工艺，从而对目标合金进行微结构调控，以期优化力学性能；第二部分以多相高熵合金为研究对象，充分考虑凝固特性与结构异质性的耦合效应，解析这种耦合效应对力学性能的作用响应和机理，并针对特定的结构特征进行相应的微结构调控，以期优化力学性能。主要研究内容和结果如下：

针对残余应力累积难题，开展了热处理对增材制造CoCrFeNiMn的组织性能调控研究。对该合金进行了不同温度下的热处理工艺，探索了热处理对亚稳态高熵合金的微结构调控潜力。研究表明通过合适的热处理工艺可以令残余应力转化为增益，诱导高熵合金产生亚微米析出相，实现跨尺度多级结构的构筑，从而提升力学性能。

针对表面粗大柱状晶难题，开展了激光冲击对增材制造AlCoCrFeNi的组织性能调控研究。详细研究了激光冲击对表面柱状晶的重塑效果，揭示了在激光冲击作用下柱状晶的变形特征和晶粒细化机制。研究表明激光冲击可以令表面柱状晶重塑为等轴晶，构筑出“等轴晶-柱状晶-等轴晶”三明治结构，从而优化了力学性能。

针对微观尺度上结构异质性与凝固特性的耦合效应，对增材制造AlCoCrFeNi_2.1共晶高熵开展了详细的变形机理研究，并进行了微观尺度上的相结构调控。深入讨论了这种耦合效应对微观结构和力学性能的影响，发现耦合效应会引发共晶双相定向排列，从而产生严重的拉压不对称现象。通过对激光功率进行优化，实现了对共晶双相的调控，从而改善了拉压不对称性行为。同时，从能量角度定义了可以量化加工硬化层面上拉压不对称的无量纲量。

针对介观尺度上结构异质性与凝固特性的耦合效应，对增材制造层压式高熵合金开展了详细的变形机理研究，并进行了介观尺度上的界面结构调控。深入讨论了界面结构对层压式高熵合金力学性能的影响，设计了多种界面间距来优化力学性能。研究发现，界面结构会产生额外的强化效应，使其力学性能优于单相高熵合金，但是其与凝固特性的耦合效应会引发严重的各向异性行为。通过将界面间距调控到合适的尺寸，成功优化了各向异性行为。

Additive manufacturing (AM), with its unique "bottom-to-up" production mode, features shortened development cycles, optimized structural designs, resource savings, and cost reductions. High-entropy alloys (HEAs), on the other hand, exhibit extensive design space and superior mechanical properties compared to conventional alloys. Combining AM with HEAs not only leverages the technological advantages of AM but also enhances the performance advantages of HEAs. This synergy paves the way for the development of advanced metal materials with high performance and functionality in the new era. Despite the promising prospects of AM-HEAs, it is still in the exploratory stage, with a series of scientific questions awaiting answers. The microstructure of AM-HEAs often exhibits complex structural characteristics. This complexity arises from two aspects: first, the typical solidification characteristics caused by non-equilibrium solidification in AM, and second, the structural heterogeneity caused by the multi-component nature of HEAs. Understanding the relationship between microstructure and macroscopic properties is the challenge that AM-HEAs must face to achieve high performance. Process determines structure, and structure determines performance. Only by selecting the appropriate processes for effective microstructure control can "shape control" be achieved. This, in turn, leads to the satisfactory optimization of mechanical properties, ensuring "performance assurance".

This study will extensively focus on the microstructure control of AM-HEAs. The research is divided into two main parts. The first part focuses on single-phase HEAs. Without considering the structural heterogeneity of HEAs, targeted post-processing techniques are applied to address the solidification characteristics induced by AM, such as residual stress and columnar grains. The aim is to design the microstructure of the target alloy to optimize its mechanical properties. The second part revolves around multiphase HEAs. Taking into account the coupling effects between solidification characteristics and structural heterogeneity, the study analyzes the response and mechanisms of these coupling effects on mechanical properties. Specific microstructure control is then applied to structural features, aiming to optimize mechanical properties. The main content and results are as follows:

To address the challenge of accumulated residual stresses, a study on the control of structures and properties of AM-CoCrFeNiMn by heat treatment is conducted. Different heat treatment processes at various temperatures are applied to explore the potential of heat treatment for microstructure control of this metastable HEA. The study demonstrates that suitable heat treatment processes can convert residual stresses into benefits, inducing the formation of sub-micron precipitates in this alloy. This leads to the construction of a multiscale hierarchical structure, thereby enhancing the mechanical properties.

To address the challenge of coarse columnar grains on the surface, a study on the control of the structures and properties of AM-AlCoCrFeNi by laser shock peening (LSP) is conducted. The research extensively investigates the reshaping effect of the LSP on surface columnar grains, revealing the deformation characteristics and grain refinement mechanism. The study demonstrates that LSP can reshape surface columnar grains into equiaxed grains, constructing an "equiaxed grain – columnar grain – equiaxed grain" sandwich structure, thereby optimizing the mechanical properties.

To address the coupling effect of structural heterogeneity and solidification characteristics at the microscopic scale, a detailed study on the deformation mechanisms of AM-AlCoCrFeNi_2.1 is conducted, along with microstructural control at the microscopic scale. The study thoroughly discusses the influence of the coupling effect on the microstructure and mechanical properties, revealing that the coupling effect can lead to eutectic biphasic directional arrangement, which results in severe tension-compression asymmetry (TCA). By optimizing the laser power, the eutectic structure is achieved to adjust, improving the behavior of TCA. Additionally, a dimensionless quantity is defined to quantify the TCA on the work hardening from an energy perspective.

To address the coupling effect of structural heterogeneity and solidification characteristics at the mesoscopic scale, a detailed study on the deformation mechanisms of the laminated HEAs fabricated by AM is conducted, along with interface control at the mesoscopic scale. The study delves into the influence of interface structure on the mechanical properties of laminated HEAs, and designs various interface spacings to optimize the mechanical properties. The research finds that the interface structure introduces additional strengthening effects, leading to superior mechanical properties compared to single-phase HEAs. However, the interface structure coupling with the solidification features will induce significant anisotropic behavior. By tailoring the interface spacing to an appropriate scale, the anisotropic behavior is successfully optimized.