The effect of cathodic current density on the microstructure of electrochemically produced nanostructured powders of NixMo1–x alloys

Nanostructured NixMo1–x alloy powders were produced by electrochemical deposition from nickel–sulphate and sodium–molybdate ammonia solutions in the current density range of 50–500 mA cm−2. The chemical composition of the powders has been found to depend on the cathodic current density for the simultaneous reactions of induced molybdenum and nickel codeposition and hydrogen evolution. As the cathodic current density increases, over the current density range of 50–500 mA cm−2, the content of molybdenum in the alloy decreases from 7 mol.% to 0.4 mol.%. The molybdenum content decreases rapidly with an increase in current density from 50 mA cm−2 to 200 mA cm−2. A further increase in current density produces a slight decrease in the molybdenum content. X-ray diffraction (XRD) analysis determined that the obtained powders contained an amorphous phase and nanocrystals arranged in a face-centred cubic lattice (FCC). The amorphous phase exists between nanocrystal grains, its percentage in the produced powders being relatively small. The size of nanocrystals is dependent on the cathodic current density for powder production and on the molybdenum content in the alloy. The increase in current density from 50 mA cm−2 to 200 mA cm−2 induces an increase in mean nanocrystal value from 13 nm to 21 nm. Further current density increases result in a decrease in the mean nanocrystal size to 17.5 nm at j = 500 mA cm−2. The size of the crystals produced in the current density range of 50–200 mA cm−2 is generally dependent on the molybdenum content in the alloy. The crystal dimensions of the powders produced at j > 200 mA cm−2 were affected by the cathodic current density. The increases in both the cathodic current density for powder production and the molybdenum content in NixMo1–x alloys resulted in a greater amorphous phase percentage and smaller crystal grains of the FCC phase with a higher density of chaotically distributed dislocations and a higher level of microstrain.