Owing to the partial dislocation assisted twinning and/or displacive transformation upon stress loading, metastable high-entropy alloys (HEAs) and their interstitial variants have shown excellent strength-plasticity synergy. However, the fundamental mechanisms of the dislocation nucleation and the onset of plasticity in these emerging materials remain unclear. The present study is to provide quantitative insights into the dislocation nucleation in the metastable HEAs and reveal the corresponding effects of interstitial alloying elements through combined instrumented nanoindentation experiments and statistical physical modeling. The results indicate that dislocation nucleation in a representative metastable non-equiatomic FeMnCoCr HEA is triggered by the thermally activated displacement of single principal atom, suggesting a dominant homogeneous mode of dislocation nucleation according to a continuum mechanical description for neonatal dislocation loop energy. Also, minor heterogeneous nucleation via monovacancy-atom exchange is possible according to a quantitative analysis for the potential effects of pre-existing defects. The activation volume necessary for dislocation nucleation in the metastable HEA is increased upon dissolving 0.5 at.% C plus 1.0 at.% N into the face-centered cubic structure. Statistical modeling and experimental nanoindentation results suggest that interstitial C and N atoms are prone to facilitate the nucleation rate of Shockley partials under intense shears. Yet, the significant drag effect by interstitial atoms can trap those neonatal mobile partials and reduce their mean free path before exhaustion. Thus, the width of stacking faults (SFs) formed by slip of such partials is severely constrained, which hinders the generation of SFs on multiple atomic layers and further inhibits the displacive phase transformation during deformation of the C-N co-doped metastable HEAs.

由于在应力加载时部分位错辅助孪晶和/或位移转变，亚稳态高熵合金（HEA）及其间隙变体已显示出出色的强度-塑性协同作用。但是，这些新兴材料中位错成核和可塑性开始的基本机制仍不清楚。本研究旨在通过结合仪器化的纳米压痕实验和统计物理建模，提供对亚稳态HEA中位错形核的定量见解，并揭示间隙合金元素的相应作用。结果表明，代表性的亚稳态非等原子FeMnCoCr HEA中的位错成核是由单个主原子的热活化位移触发的，根据连续位错力学描述新生儿位错环能量，表明位错成核的主要均质模式。同样，根据对先前存在缺陷的潜在影响的定量分析，通过单空位-原子交换的少量异质成核也是可能的。通过将0.5％（原子）的C + 1.0％（原子）的N溶解到面心立方结构中，可以增加亚稳态HEA中位错成核所需的活化体积。统计模型和实验纳米压痕结果表明，间隙C和N原子易于在强烈剪切作用下促进Shockley部分的成核速率。然而，间质原子的显着拖曳效应会困住这些新生儿的可移动部分，并减少精疲力竭前的平均自由程。从而，