The underlying atomistic mechanism of deformation is a central problem in mechanics and materials science. Whereas deformation of crystalline metals is fundamentally understood, the understanding of deformation of amorphous metals lacks behind, particularly identifying the involved temporal and spatial scales. Here, we reveal that at small scales the size-dependent deformation behavior of amorphous metals significantly deviates from homogeneous flow, exhibiting increasing deformation rate with reducing size and gradually shifted composition. This transition suggests the deformation mechanism changes from collective atomic transport by viscous flow to individual atomic transport through interface diffusion. The critical length scale of the transition is temperature dependent, exhibiting a maximum at the glass transition. While viscous flow does not discriminate among alloy constituents, diffusion does and the constituent element with higher diffusivity deforms faster. Our findings yield insights into nano-mechanics and glass physics and may suggest alternative processing methods to epitaxially grow metallic glasses.

变形的基本原子机制是力学和材料科学的中心问题。虽然从根本上理解了晶体金属的变形，但对非晶金属变形的理解却很落后，特别是确定所涉及的时间和空间尺度。在这里，我们发现，在小尺度上，非晶态金属的尺寸依赖性变形行为显着偏离均匀流动，表现出随着尺寸的减小和成分的逐渐变化而增加的变形率。这种转变表明变形机制从通过粘性流的集体原子输运转变为通过界面扩散的单个原子输运。转变的临界长度尺度取决于温度，在玻璃化转变时表现出最大值。虽然粘性流不会区分合金成分，但扩散会区分，并且扩散率较高的成分元素变形速度更快。我们的研究结果为纳米力学和玻璃物理学提供了深入的见解，并可能提出外延生长金属玻璃的替代加工方法。