Solid-state interfacial reaction and asymmetric growth of amorphous interlayers in Ni/Nb multilayers. Molecular-dynamics simulation together with experiments

An embedded-atom potential for the Ni-Nb system is constructed using physic al properties obtained from first-principle calculations. Employing the pot ential, molecular-dynamics simulations are performed to study the interfaci al reaction in Ni/Nb multilayers upon annealing at medium temperatures. The results show that a preset disordered interlayer, which is obtained by exc hanging Ni and Nb atoms in the interfaces, may act as a nucleus of amorphou s phase and is usually necessary for amorphization. It is found that the gr owth of the amorphous interlayer is in a planar mode and exhibits an asymme tric behavior due to a faster consumption of Ni than that of the Nb layer; this is also indeed observed experimentally. Moreover, performing a simulat ion with solid solution models, it is found that the Nb lattice can accommo date a large number of Ni atoms and still retain a crystalline structure, w hile a small amount of Nb atoms induce a spontaneous decay of the Ni lattic e. Such differences in solid solubility is thought to be the physical origi n of the asymmetric growth observed in experiments and simulations.