The microstructural evolution of a metastable face centered cubic (FCC) Fe₄₀Co₂₀Cr₂₀Mn₁₀Ni₁₀ high-entropy alloy (HEA) under both tension and compression is systemically investigated. The results show much higher level of martensite phase transformation from FCC structure to hexagonal closed packed (HCP) structure under compression than tension, indicating a distinct tension-compression asymmetry. The compressive tests underwent higher true stresses, which further provided stronger driving forces to trigger the phase transformation than those in tensile tests. Except for the martensite phase transformation, dislocation planar slip prevails in both tension and compression, along with the occasional formation of mechanical twins. Dislocation slip dominates the whole tensile deformation, while both dislocation motions and martensite phase transformation play critical roles in the compressive deformation. The martensite phase transformation is preferred to nucleate at grain or subgrain boundaries due to a medium stacking fault energy (SFE) of ∼20 mJ m⁻². The formation of HCP phase via partial dislocation emission from low angle grain boundaries offers additional pathways for martensite phase transformation. Our study thus remarkably benefits the understanding of the de formation mechanisms of metastable HEAs.

亚稳面心立方（FCC）Fe ₄₀ Co ₂₀ Cr ₂₀ Mn ₁₀ Ni _10的组织演变系统地研究了拉伸和压缩状态下的高熵合金（HEA）。结果表明，在压缩状态下，马氏体从FCC结构向六方密堆积（HCP）结构的相变程度要比张力高得多，表明存在明显的张力-压缩不对称性。压缩试验承受的真实应力更高，与拉伸试验相比，其提供了更大的驱动力来触发相变。除马氏体相变外，位错平面滑移在拉伸和压缩过程中均占优势，并偶尔形成机械孪晶。位错滑移控制着整个拉伸变形，而位错运动和马氏体相变都在压缩变形中起关键作用。⁻²。通过低角度晶界的部分位错发射形成HCP相，为马氏体相变提供了其他途径。因此，我们的研究显着有益于了解亚稳态HEA的形成机理。