Sequential disordering of crystalline lattices in the Ni–Nb multilayers upon solid-state interfacial reaction

Sequential disordering of the original Ni and Nb crystalline lattices in the as-deposited Ni–Nb multilayers was observed, for the first time, in the early stage of solid-state interfacial reaction conducted on a hot-stage in a transmission electron microscope. It was the origin of a predicted or observed asymmetric growth of amorphous interlayer in solid-state amorphization in some binary metal systems. The interfacial reaction proceeds with increasing annealing temperature and time, and solid-state amorphization eventually dominates in the Ni48Nb52 multilayers, whereas a new HCP metastable crystalline phase was obtained in the Ni70Nb30 multilayers. A reasonable interpretation to the formation of the amorphous and HCP phases is given by a calculated Gibbs-free-energy diagram of the Ni–Nb system.