The effect of lamellar orientation on the deformation behavior of eutectic high entropy alloy at the micrometer scale, and the roles of two rarely explored laminate orientations (i.e., the lamellar orientation at ∼ 0° and 45° angles with the loading direction) in regulating size-dependent plasticity were investigated using in-situ micropillar compression tests. The alloy, CoCrFeNiTa_0.395, consists of alternating layers of Laves and FCC phases. It was found that the yield stress of the 0° pillars scaled inversely with the pillar diameters, in which the underlying deformation mode was observed to transform from pillar kinking or buckling to shear banding as the diameter decreased. In the case of the 45° pillars with diameters ranging from 0.4 to 3 μm, there exists a ‘weakest’ diameter of ∼ 1 μm, at which both constraint effect and dislocation starvation are ineffective. Irrespective of the lamellar orientations, the strain hardening rate decreased with decreasing pillar diameter due to the diminishing dislocation accumulation that originated from the softening nature of large shear bands in the 0° pillars, and the enhanced probability of dislocation annihilation at the increased free surfaces in the 45° pillars. The findings expand and deepen the understanding of the mechanical size effect in small-scale crystalline materials and, in so doing, provide a critical dimension for the development of high-performing materials used for nano- or microelectromechanical systems.

层状取向对共晶高熵合金在微米尺度上的变形行为的影响，以及两个很少探索的层状取向（即与加载方向成约0°和45°角的层状取向）在调节尺寸中的作用依赖可塑性使用原位微柱压缩试验进行了研究。合金CoCrFeNiTa _0.395由Laves和FCC相的交替层组成。发现0°支柱的屈服应力与支柱直径成反比，其中随着直径减小，观察到基本变形模式从支柱扭结或屈曲转变为剪切带。对于直径为0.4到3μm的45°支柱，“最弱”直径约为1μm，在这种情况下，约束效应和位错饥饿都无效。无论层状取向如何，由于位错积累的减少（由于0°柱中大剪切带的软化性质）以及位错an灭在增加的自由表面上的可能性增加，导致应变硬化速率随柱直径的减小而降低。 45°支柱。