Effect of additional solutes on the vacancy-mediated diffusion of Mg in biodegradable Zn-based alloys: A first-principles study

Zn-Mg alloys show great potential in the fabrication of biodegradable implants. However, due to the quick diffusion of Mg, their mechanical properties tend to exhibit evident variations during room-temperature storage. To suppress this phenomenon, the influence of additional solute X (X = Mn, Cu, Al, Ag and Li) on the vacancy- mediated diffusion of Mg is investigated by first-principles calculations in combination with the climbing image nudged elastic band method. It is found that the vacancy formation energy and migration energy of Mg diffusion are strongly dependent on the Va-Mg-X configurations and solute X. Due to the strong atomic bonding between Mg and Mn, Mn is the only element that simultaneously increases the average activation energies of in-plane and out-of-plane diffusion of Mg. Moreover, the migration of Mg becomes direction-dependent in the vicinity of solute X. It is easier for Mg to enter the 1NN sites of Mn, Cu, Ag and Li than to leave them. Collectively, proper addition of Mn is recommended for developing Zn-based alloys with enhanced stability of mechanical properties.