Statistical physics of dislocation nucleation by nanoindentation

Abstract

Current understanding of the onset of plasticity during nanoindentation of crystalline materials involves homogenous dislocation nucleation in the crystal underneath the indenter. Through the use of cutting-edge nanoindentation techniques, this study examines the initiation of plastic deformation in single crystal oriented platinum samples. Variations in the temperature and loading rate during indentation reveal temporal and thermal dependencies, and support the stochastic and thermally-activated nature of the initial plastic event. These dependencies of dislocation nucleation are precisely quantified by developing analysis methods based on statistical thermodynamics, and are used to evaluate the probability of various atomistic mechanisms. The results of this procedure implicate a critical activation event occurring in a single atomic volume, with an activation enthalpy of a fraction of an electron volt. These findings strongly indicate that the initiation of plasticity begins with a heterogeneous dislocation nucleation event, in conflict with the current belief, and significantly advance understanding of the onset of plastic deformation during nanoindentation.