Solid-state amorphization in Ni/Mo multilayers studied with molecular-dynamics simulation

An n-body potential for the Ni-Mo system is constructed based on the Finnis-Sinclair formalism by using the physical properties obtained from first-principle calculations. Employing the potential, a molecular-dynamics simulation is performed to reveal the amorphization process in the Ni-Mo multilayers upon annealing at medium temperatures ranging from 300 to 600 °C. Six sandwich models consisting of atomic planes with various orientations and one bilayer model are simulated to investigate the effect of interfacial texture on amorphization and the related growth kinetics. It is found that when the sandwich model has a semicoherent interface consisting of both Ni and Mo close-packed planes, amorphization is frustrated even up to a temperature of 600 °C. Simulation results show that in all the other models with or without a preset disordered interlayer, amorphization can take place at a temperature down to 350 °C and is initiated through a crossing-interface atomic diffusion, diffusion-induced alloying and subsequent growth of the interfacial amorphous layer, resulting eventually in forming a uniform amorphous phase. Concerning the kinetics, the growth of the amorphous layer is found to follow exactly a $t^{1/2}$ law, indicating that solid-state amorphization is indeed through a diffusion-limited reaction. In addition, an asymmetric behavior is observed that the growing speed towards Ni is greater than that directed to the Mo lattice.