Mechanisms of localized pulsed electrodeposition (L-PED) for microscale 3D printing of nanotwinned metals

Nanotwinned metals (nt-metals) show larger ductility and strength compared to nanocrystalline metals facilitated by their special microstructure containing arrays of parallel twin boundaries. The recently-introduced localized pulsed electrodeposition (L-PED) enables 3D printing of nt-metals in complex geometries. Herein, the first computational model incorporating all the involved physics (i.e. electrodeposition, evaporation, fluid flow, and heat transfer) in the L-PED process is presented. The model reveals the critical rules of the pulsed signal and evaporation-driven convection flux in the mass transport mechanism, ion concentration, current density, and printing rate in the L-PED process. Notably, the simulation results predict a very high peak current density (∼130 times of the average current density) during the short (∼ms) ON-time. This high current density in a short period of ON-time results in high deposition rate, of possibly a metal with high internal stress. This prediction may explain the current hypotheses in the literature on formation of nt-metals by stress relaxation during the OFF-time.