Oxidation of Ni-W coatings at 700 and 800 °C in air

The oxidation of Ni-(12-18 at.%)W coatings electrodeposited on steel was studied at 700 and 800 °C in air. The coatings oxidized with similar rates, and displayed poorer oxidation resistance than bulk Ni, probably due mainly to the formation of NiWO4. The oxidation resulted in the formation of an outer NiO layer by outward transport of Ni, and an inner (NiO+NiWO4) mixed oxide layer by the inward diffusion of oxygen. At the same time, the outward diffusion of Fe toward the coating surface occurred, eventually resulting in the formation of Fe2O3 and NiFe2O4 in the outer NiO layer.