DFT study on the adsorption and absorption behaviors of liquid nitrogen in the Mg nano alloys synthesized from powder metallurgy

Abstract

Mg-based metal-matrix nanocomposites (MMNCs) are lauded as one of the most promising structural materials for vehicle, military, and construction applications. These Mg MMNCs are often synthesized using the powder metallurgy (PM) process under liquid nitrogen cryogenic environments to control the grain sizes. It is believed that proper incorporation of the nitrogen species into the bulk lattice during processing could strongly enhance the mechanical properties of MMNCs by forming N-rich dispersoids. In this work, using the density-functional theory (DFT), we have studied the adsorption and absorption phenomena of liquid nitrogen molecule/atoms that can be applied to the Mg MMNC PM processing. The study includes the impacts of binding sites, alloying elements (Al, Zn, and Y), and surface crystallographic planes on the nitrogen molecule adsorption energies. We also examined the transition state (TS) behaviors for the bond breaking and lattice diffusion of nitrogen. The results show that ∼1.13eV would be required for nitrogen molecule to break the triple bonding and to diffuse into the Mg bulk lattice. Also, it was found that addition of Y can greatly enhance the binding strength of N2 molecule on the Mg surface.