Cross Graham L W, Schirmeisen André, Grütter Peter, Dürig Urs T
SFI Trinity Nanoscience Laboratory, Department of Physics, Trinity College, Dublin 2, Ireland.
Nat Mater. 2006 May;5(5):370-6. doi: 10.1038/nmat1632. Epub 2006 Apr 16.
Spatially localized stress fields produced by instrumented, sharp indentation probes are a route to testing the mechanical properties of materials at the smallest length scales. Here we provide direct experimental measurement of indentation plasticity with contact strain fields involving up to a few thousand atoms. We observe two types of nanoscale plasticity: on the pristine surface, high-resolution sensing shows an overall smooth, remarkably reversible indentation response interjected by sudden discrete drops in indenter load. The jumps often occur in pairs with pop-in motion during loading healed by a corresponding pop-out motion on the unload stroke to define a compact hysteresis loop. Despite the general reversibility, cyclic indentation at a single sample position leads to a subtle plastic ratchet and shakedown behaviour with displacements correlated to the underlying gold lattice constant. Our results concur with a previously established picture of thermally activated atomistic plasticity, but suggest a new mechanism at reduced scales that suppresses permanent mass transport.
由仪器化的尖锐压痕探针产生的空间局部应力场是在最小长度尺度上测试材料力学性能的一种途径。在此，我们通过涉及多达数千个原子的接触应变场，对压痕塑性进行了直接实验测量。我们观察到两种类型的纳米尺度塑性：在原始表面上，高分辨率传感显示出整体平滑、显著可逆的压痕响应，但压头载荷会突然出现离散下降。这些跳跃通常成对出现，加载过程中的突入运动在卸载行程中通过相应的弹出运动得以恢复，从而形成一个紧凑的滞后回线。尽管总体上具有可逆性，但在单个样品位置进行循环压痕会导致微妙的塑性棘轮和安定行为，其位移与底层金晶格常数相关。我们的结果与先前确立的热激活原子塑性图景一致，但表明在更小尺度上存在一种抑制永久质量传输的新机制。
