CrCoNi中熵合金的低温力学性能接近目前已知金属材料强度和韧性的综合极限，使得其在低温极端环境应用领域潜力巨大。然而，选区激光熔化制备CrCoNi中熵合金仍面临组织柱状外延生长及含氧量偏高等问题，严重影响强韧性能。本项目拟引入LaB6对CrCoNi中熵合金掺杂，原位生成La2O3颗粒作为形核质点促进等轴晶生长细化晶粒，同时降低增材组织含氧量，达到增强增韧的目的。系统研究LaB6增强CrCoNi中熵合金材料设计与选区激光熔化制备、激光熔池中LaB6分解氧化行为与La2O3析出分布规律、CrCoNi中熵合金增材组织熔凝转变行为及调控方法、LaB6增强CrCoNi中熵合金室温和低温力学性能与形变失效机制，从而揭示选区激光熔化制备LaB6增强CrCoNi中熵合金的物理化学过程及组织熔凝行为，阐明协同强韧化机理，为新型高强韧CrCoNi中熵合金体系的开发与应用奠定理论和技术基础。

Equiatomic CrCoNi medium entropy alloy (MEA) has excellent cryogenic mechanical properties including high strength and toughness, approaching the best combinations of strength, ductility and toughness on record. These advantages endow it great potential in cryogenic extremes such as aerospace and petrochemical industry etc. However, columnar epitaxial growth and high oxygen content in selective laser melting (SLM) of CrCoNi MEA greatly deteriorate its quality and mechanical properties. In this project, to solve these problems in SLM, we propose a novel idea that introduces LaB6 into CrCoNi to in-situ precipitate La2O3 particles, which will act as nucleation sites during solidification of CrCoNi MEA in molten pool, facilitating the growth of fine dense equiaxial grain. Simultaneously, oxygen content in SLM CrCoNi MEA matrix will be reduced. The design principle of LaB6 reinforced CrCoNi MEA composite powder and fabrication parameters of SLM will be systematically investigated. The decomposition, oxygen absorption behavior of LaB6 and precipitation, distribution morphology of in-situ precipitated La2O3 nano-particles will be investigated. The solidification and microstructure transition behavior of SLM fabricated LaB6 reinforced CrCoNi MEA will be clarified. The mechanical properties, deformation and failure mechanism of LaB6 reinforced CrCoNi MEA in both cryogenic and room temperature will be revealed. By aforementioned researches on SLM CrCoNi MEA, we are able to establish a microstructure control strategy and fabricate high quality CrCoNi MEA components with high strength and high toughness, which are essential for developing wider application fields. The outcomes of this project will not only provide a new material system of high strength and high toughness CrCoNi MEA for SLM, but also provide a novel idea to solve columnar epitaxial growth and high oxygen content in laser additive manufacturing.