ABSTRACT Molecular dynamics simulations were used to study the atomic mechanisms of deformation of nanocrystalline gold with 2.65–18 nm in grain size to explore the inverse Hall–Petch effect. Based on the mechanical responses, particularly the flow stress and the elastic-to-plastic transition, one can delineate three regimes: mixed (10–18 nm, dislocation activities and grain boundary sliding), inverse Hall-Petch (5–10 nm, grain boundary sliding), and super-soft (below 5 nm). As the grain size decreases, more grain boundaries present in the nanocrystalline solids, which block dislocation activities and facilitate grain boundary sliding. The transition from dislocation activities to grain boundary sliding leads to strengthening-then-softening due to grain size reduction, shown by the flow stress. It was further found that, samples with large grain exhibit pronounced yield, with the stress overshoot decrease as the grain size decreases. Samples with grain sizes smaller than 5 nm exhibit elastic-perfect plastic deformation without any stress overshoot, leading to the super-soft regime. Our simulations show that, during deformation, smaller grains rotate more and grow in size, while larger grains rotate less and shrink in size.

中文翻译：

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小尺寸纳米晶金：混合态和超软态之间的反霍尔-佩奇

摘要 分子动力学模拟用于研究晶粒尺寸为 2.65-18 nm 的纳米晶金变形的原子机制，以探索逆霍尔-佩奇效应。基于机械响应，特别是流动应力和弹塑性转变，可以描述三种状态：混合（10-18 nm，位错活动和晶界滑动），逆霍尔-佩奇（5-10 nm，晶界滑动）和超软（低于 5 nm）。随着晶粒尺寸的减小，纳米晶固体中存在更多的晶界，这会阻止位错活动并促进晶界滑动。从位错活动到晶界滑动的转变导致由于晶粒尺寸减小而导致的强化然后软化，如流变应力所示。进一步发现，具有大晶粒的样品表现出明显的屈服，随着晶粒尺寸的减小应力超调减小。晶粒尺寸小于 5 nm 的样品表现出完美的弹性塑性变形，没有任何应力超调，导致超软状态。我们的模拟表明，在变形过程中，较小的晶粒旋转得更多并且尺寸增大，而较大的晶粒旋转得更少并且尺寸缩小。