The internal friction of Cu50Zr50 metallic glass nano-pillars was investigated by using molecular dynamics simulations. An unusual non-monotonic variation of internal friction is revealed against the size of the specimen, which differs significantly from that of the bulk metallic glass. Meanwhile, by analyzing the rearranged atoms with high mobility, which play a vital role in affecting the internal friction, it is found that the rearrangement of surface atoms is more significant than that of the bulk ones, and their fraction depends on the sample size as well. With reducing the sample size, the fraction of rearranged atoms in the surface region increases, which could be described by an exponential equation. This finding suggests that the size dependence of internal friction originates directly from the different fractions of the rearranged atoms in the surface region of nano-pillars. Furthermore, a phenomenological model was established to describe the internal friction of the nano-pillars against their diameters. The presented results provide a quantitative insight into the size effect on internal friction in nanoscale metallic glasses, also shedding light on the atomistic mechanism of surface relaxation of amorphous solids.

中文翻译：

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纳米级金属玻璃中的异常内摩擦及其尺寸依赖性

通过分子动力学模拟研究了Cu50Zr50金属玻璃纳米柱的内摩擦。内摩擦的不寻常的非单调变化与试样的尺寸显着不同，这与大块金属玻璃的尺寸显着不同。同时，通过分析对内摩擦起重要作用的具有高迁移率的重排原子，发现表面原子的重排比块体的重排更显着，它们的比例取决于样品大小，如出色地。随着样本量的减少，表面区域中重排原子的比例增加，这可以用指数方程来描述。这一发现表明内摩擦的尺寸依赖性直接源于纳米柱表面区域中不同比例的重排原子。此外，建立了一个现象学模型来描述纳米柱与其直径的内摩擦。所呈现的结果提供了对纳米级金属玻璃内摩擦的尺寸效应的定量洞察，也揭示了非晶固体表面弛豫的原子机制。