Guidance to design grain boundary mobility experiments with molecular dynamics and phase-field modeling

Quantitative phase-field modeling can play an important role in designing experiments to measure the grain boundary (GB) mobility. In this work, molecular dynamics (MD) simulation is employed to determine the GB mobility using Cu bicrystals. Two grain configurations are considered: a shrinking circular grain and a half-loop grain. The results obtained from the half-loop configuration approach asymptotically to that obtained from the circular configuration with increasing half-loop width. We then verify the phase-field model by direct comparison to the MD simulation results, obtaining excellent agreement. Next, this phase-field model is used to predict the behavior in a common experimental setup that utilizes a half-loop grain configuration in a bicrystal to measure the GB mobility. With a 3-D simulation, we identify the two critical times within the experiments to reach an accurate value of the GB mobility. We use a series of 2-D simulations to investigate the impact of the notch angle on these two critical times. We also show that if the notch does not have a sharp tip, it may immobilize the GB migration indefinitely. Finally, we demonstrate that our approach for the quarter-loop configuration eliminates some disadvantages of the half-loop.