Prediction of dislocation nucleation during nanoindentation of Al₃Mg by the orbital-free density functional theory local quasicontinuum method

The first-principles prediction of dislocation nucleation in metallic systems subject to realistically sized indenters requires a multiscale approach due to the prohibitive computational expense. The largest empirical atomistic simulations include at most a billion atoms, at the same time requiring the parameterization of new interactions whenever an additional species or crystal structure is added. The multiscale orbital-free density functional theory–local quasicontinuum (OFDFT-LQC) method overcomes these problems by using first-principles OFDFT to capture the atomic interactions while relying upon LQC to evolve the macroscopic system. We use this method to indent the (111) surface of a 2×2×1μm piece of L12 Al3Mg. Using a localization criterion, the first dislocation is predicted to form off-axis on the slip plane in the direction after the indenter has penetrated 70 nm. Other popular dislocation nucleation criteria give different predictions. These results are strikingly similar to those for indentation into the (111) surface of Al, indicating that the underlying crystal structure, not the atomic identity, is the most important factor in determining the onset of plasticity.