Origins of strengthening in complex metal alloys from full-scale MD simulations

We present a series of massive (~10⁸ atoms) Molecular Dynamics (MD) simulations reproducing full complexity of plastic strength response in concentrated single-phase body-centered cubic (BCC) solid solutions and devised to explore the space of alloy compositions in order to maximize their mechanical strength. To efficiently navigate our search towards mechanically strong alloy compositions, we employ iterative optimization using Gaussian process regression. Many of the simulated RCCA compositions exhibit well pronounced cocktail strengthening. To further clarify the nature of alloy strengthening we develop a method of “computational alchemy” in which interatomic interactions are modified to continuously and systematically vary two key parameters defining SSS – atomic size misfit and elastic stiffness misfit – over a maximally wide range of misfit values. At variance with views prevailing in the literature, our large-scale computational experiments show that stiffness misfit can contribute to SSS on par if not more than size misfit. Furthermore, depending on exactly how they are combined, the two misfits can result in synergistic (amplification) or antagonistic (compensation) effect on alloy strengthening. Our data suggests that, just like in unalloyed BCC metals, motion of screw dislocations plays a dominant role alloy strengthening.