Microstructure of amorphous electrodeposited Co-Ni-W films

Abstract

The phase composition of electrodeposited films of (Co_{100 − x} -Ni _x )_{100 − y} W _y alloys (x = 0–100 at % Ni, y = 0–30 at % W), the microstructures of amorphous films of this system on the submicrometer and nanometer scales, and the mechanism of their nucleation and growth are studied. X-ray diffraction analysis demonstrates that, as the tungsten concentration increases, the transition from a crystalline into an amorphous state in the films based on Co-W alloys occurs through a supersaturated hcp solid solution, whereas this transition in the films based on Ni-W alloys occurs through an fcc structure. Heterophase states consisting of a mixture of hcp and fcc structures are observed in the composition range x = 30–80 at % Ni, and, at concentrations higher than 12–14 at % W, an amorphous phase is also observed. A homogeneous amorphous phase forms at a refractory-metal content of 19–20 at % or more. Transmission and scanning electron microscopies show that the amorphous Co-W, Ni-W, and Co-Ni-W films have a network structure. The laws of the variation of the network microstructure with the chemical composition of the amorphous films are established and explained in the framework of the island model of thin film nucleation and growth.