Experimental and numerical investigations of Ni–Co–SiO2 alloy films deposited by magnetic-field-assisted jet plating

A new method of magnetic-field-assisted jet plating is presented to manufacture Ni-Co-SiO2 alloy films. The influence of different concentrations of Co2+ ions of the electrolyte is investigated with and without magnetic field to study the resulting properties of the deposits. The texture orientation, surface morphology, magnetic properties and corrosion resistance of the alloy films were characterized. The results show that with increasing Co2+ concentration in conventional jet-plating, the surface morphology changes from a granular crystal structure to a needle-like structure at 30 g/L caused by the hexagonal close-packed (HCP) structure of a large Co content. Differently, the assistance of the magnetic field leads to lower Co content in the films, even at a high Co2+ concentration of 30 g/L. The deposit layer remains in the face-centered cubic (FCC) structure and shows a granular morphology. The magnetic field in general leads to grain refinement and inhibits the abnormal Ni–Co co-deposition. The Ni–Co–SiO2 alloy films obtained by magnetic-field-assisted jet plating have a smooth and dense surface. The best soft magnetic properties and corrosion resistance are obtained at a Co2+ concentration of 20 g/L. The coercivity is as low as 7.5 Oe, and the corrosion current density is as low as 1.12 μA·cm-2 in 3.5 wt% NaCl solution without agitation and at room temperature, clearly showing the advantages of the method for preparing superior soft magnetic materials. In addition, a physical model of magnetic-field-assisted jet plating is established. The magnetic forces and the resulting electrolyte flow are analyzed with the help of numerical simulations, and the influence of the magnetic field on the deposition process is discussed from the perspective of magnetohydrodynamics.