Nature Materials

Plasticity, healing and shakedown in sharp-asperity nanoindentation

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Localized plastic stress fields produced on materials by sharp indentation probes, was investigated experimentally. Indentation was carried out on large, atomically flat gold (111)-oriented terraces that exhibited herringbone surface reconstruction. force was determined by a 110-N/m stiffness cantilever beam deflection that was measured by an in situ two-beam differential interferometer the measured the angle of cantilever bending at the point of tip contact. A positive 100-mV potential was maintained from tip to sample. The tip and sample were carefully brought into close proximity by tunnel current regulation. The changing behavior under indentation cycling at a single surface location indicated plastic ratcheting leading to a limiting shakedown.