Grain Boundary Effects in Dealloying Metals: A Multi-Phase Field Study
A multi-phase field model is employed to study the microstructural evolution of an alloy undergoing liquid dealloying. The model proposed extends upon the original approach of Geslin et al. to consider dealloying in the presence of grain boundaries. The model is implemented using a semi-implicit time stepping algorithm using spectral methods, which enables simulating large 2D and 3D domains over long time-scales while still maintaining a realistic interfacial thickness. The model is exercised to demonstrate a mechanism of coupled grain-boundary migration to maintain equilibrium contact angles with this topologically-complex solid-liquid interface during dealloying. This mechanism locally accelerates dealloying by dissolving the less noble alloy metal from (and rejecting the more noble metal into) the migrating grain boundary, thereby enhancing the diffusion-coupled-growth of the liquid channel into the precursor. The deeper corrosion channel at the migrating grain boundary asymmetrically disrupts the ligament connectivity of the final dealloyed structure, in qualitative agreement with published experimental observations. It is shown that these grain boundary migration-assisted corrosion channels form even for precursors with small amounts of the dissolving alloy species, below the so-called \textit{parting limit}