Three-dimensional molecular dynamics analysis of atomic-scale indentation

The complete atomic-scale indentation cycle is analyzed using molecular dynamics simulations. A hysteresis is observed in the instantaneous normal force versus surface separation distance curve obtained with an atom or a rigid tip indenting and, subsequently, retracting from a dynamic face-centered-cubic substrate consisting of argon or copper. The generation of irreversible deformation in a Lennard-Jones solid is revealed in light of simulation results for indentation by a single atom. The direction of irreversible deformation is shown to coincide with that of macroscopic plastic flow. The compressive yield strength decreases with increasing substrate temperature and decreasing indentation speed. The phenomena of tip wetting by substrate atoms and connective neck formation, elongation, and rupture at the tip/substrate interface are elucidated by simulation results for the unloading process. It is shown that energy dissipation decreases as the substrate temperature increases and the energy consumed by irreversible deformation is always greater than that due to heating.