Medium-entropy alloys exhibit remarkable strengthening effects owing to their large solid-solution strength, providing high potential for further improvement of the mechanical properties by distributing secondary strengthening phases. In this respect, an equiatomic VCoNi alloy is an appropriate model alloy owing to its yield strength of approximately 1 GPa, with contributions from lattice and grain boundaries. However, the adoption of precipitation hardening is challenging because the solid-solution phase region is limited, which is obtainable only at high temperatures. In this study, Mo is used to generate strengthening phases and expand the region of a face-centered cubic (FCC) solid-solution phase at lower temperatures. The 10 at% Mo, determined through thermodynamic calculations, has little effect on solid-solution states. In low-temperature aging treatments, an ordered FCC (L1₂) phase forms first followed by the formation of intermetallic μ and κ phases, which are developed under prolonged heat treatment of up to 48 h. L1₂, which cannot be expected by thermodynamic calculations as an intermediate phase, results in remarkable strengthening effects with a slight reduction in tensile ductility. However, the (Co,Ni)₃V-κ phase grows into the grain interiors and along the FCC grain boundaries forming lamellar structures with μ phase, which reduces ductility and increases strength. Thus, this work suggests that the Mo substitution to V overcomes the limitations of the VCoNi alloy and provides second-phase strengthening by forming homogeneous L1₂ within a large fraction of the FCC matrix; however, an appropriate heat treatment is required to prevent brittleness by suppressing grain-boundary μ and κ phases.

中熵合金由于其固溶强度大而表现出显着的强化效果，通过分布二次强化相为进一步改善力学性能提供了很大的潜力。在这方面，等原子 VCoNi 合金是一种合适的模型合金，因为它的屈服强度约为 1 GPa，并有晶格和晶界的贡献。然而，采用沉淀硬化具有挑战性，因为固溶体相区域是有限的，只能在高温下获得。在本研究中，Mo 用于生成强化相并在较低温度下扩大面心立方 (FCC) 固溶体相的区域。通过热力学计算确定的 10 at% Mo 对固溶体状态几乎没有影响。₂ ) 首先形成相，然后形成金属间化合物 μ 和 κ 相，这些相在长达 48 小时的长时间热处理下形成。L1 ₂是通过热力学计算无法预期的中间相，导致显着的强化效果，同时拉伸延展性略有降低。然而，(Co,Ni) ₃ V-κ 相生长到晶粒内部并沿着 FCC 晶界形成具有 μ 相的层状结构，这降低了延展性并增加了强度。因此，这项工作表明 Mo 取代 V 克服了 VCoNi 合金的局限性，并通过形成均匀的 L1 _{2来提供第二相强化。}在大部分 FCC 矩阵中；然而，需要适当的热处理以通过抑制晶界 μ 和 κ 相来防止脆性。