Molecular dynamics study of solid state interfacial reaction in the Ni-Mo system

Abstract

Based on the Finnis–Sinclair formalism, an n-body Ni-Mo potential is constructed and the potential with optimized parameters is able to reproduce some physical properties of several Ni-Mo alloy phases. Molecular dynamics simulation with the constructed potential is performed to study the detailed process of solid-state interfacial reaction in the Ni/Mo multilayers upon isothermal annealing at medium temperatures. It is found that in the sandwich model or the bilayer model, interfacial reaction can take place down to 350 °C and is initiated through interface-crossing atomic diffusion, resulting in alloying and amorphization. The planar growth of the amorphous interlayer shows an asymmetric behavior, i.e., consuming the Ni lattice at a higher speed than the Mo lattice, leading to some intermediate stages where an Ni-enriched amorphous phase coexists with a small amount of unreacted Mo crystal. Moreover, it is revealed that 21 at.% Mo atoms in the Ni lattice reaches a critical value, resulting in a crystal-to-amorphous transition, while the critical concentration for collapsing of the Mo lattice is up to 25 at.% Ni. It follows that the above difference in the solubilities is regarded as the physical origin of asymmetric growth. Kinetically, the growth of the amorphous layer is found to follow a t1/2 law, indicating that solid-state amorphization is indeed through a diffusion-limited reaction.