A series of (CoCrNi)_100–xGd_x (x = 0/0.1/0.3/0.5/1.0) medium entropy alloys (MEAs) was fabricated by high-vacuum arc melting. The effects of rare-earth element, Gd, additions on the evolution of microstructures and mechanical properties of CoCrNi MEAs were studied. The phase and microstructure were examined using X-ray diffraction, scanning electron microscope and transmission electron microscope. The tensile properties were measured by material testing system (MTS) and the hardness was measured by both Vickers indenter and nanoindentation. As the Gd concentration increased, the phase transformed from face-centered cubic (FCC) to hexagonal close-packed (HCP) precipitates in FCC matrix. Compared to the single phase CoCrNi MEA with the yield strength of 400 MPa and fracture strength of 880 MPa, CoCrNi_99.5Gd_0.5 MEA exhibited a much higher yield strength of 751 MPa and ultimate tensile strength of 1216 MPa, while the ductility still maintained a high value of ∼55%. The enhanced mechanical properties were ascribed to solid solution, precipitation and grain refinement strengthening mechanisms. The relations among compositions, microstructures and mechanical properties of (CoCrNi)_100–xGd_x MEAs were discussed.

一系列 (CoCrNi) _{100– x} Gd _x ( x = 0/0.1/0.3/0.5/1.0) 中等熵合金 (MEAs) 是通过高真空电弧熔炼制备的。研究了稀土元素 Gd 添加对 CoCrNi MEA 微结构演变和力学性能的影响。使用X射线衍射、扫描电子显微镜和透射电子显微镜检查物相和微观结构。拉伸性能通过材料测试系统（MTS）测量，硬度通过维氏压头和纳米压痕测量。随着 Gd 浓度的增加，相从面心立方 (FCC) 转变为密排六方 (HCP) 沉淀物。与屈服强度为 400 MPa、断裂强度为 880 MPa 的单相 CoCrNi MEA 相比，CoCrNi _99.5 Gd _0.5MEA 表现出更高的屈服强度 751 MPa 和极限抗拉强度 1216 MPa，而延展性仍保持约 55% 的高值。增强的机械性能归因于固溶体、析出和晶粒细化强化机制。讨论了(CoCrNi) _{100– x} Gd _x MEA的成分、微观结构和机械性能之间的关系。