Fe-, Ni-containing ceramic-like PEO coatings on titanium and aluminum: Comparative analysis of the formation features, composition and ferromagnetic properties

Abstract

Fe-, Ni-containing coatings have been formed on aluminum and titanium by the plasma electrolytic oxidation (PEO) technique in slurry electrolytes containing colloidal particles of Fe(III) and Ni(II) compounds including hydroxides. Their composition, surface morphology, and magnetic properties were studied and compared. In both cases, the concentration of iron, nickel, and substrate metal is higher, and the oxygen concentration is lower in the pores of the coatings than their average concentration over the surface. In the case of titanium, the electrolyte and substrate metals are concentrated in the pores (at. %: 38.6 Fe, 4.7 Ni, 19.5 Ti) in the form of micro- and nanosized crystallites. In the pores of the coating on aluminum, metals are concentrated in the composition of the layers lining the pores (at. %: 15.3 Fe, 50.6 Ni, 18.8 Al). The values of the coercive force and the saturation magnetization of the ferromagnetic component at 300 K for the aluminum sample (Нс = 38 Oe, M*s = 2.8 × 10−4 emu/g) are significantly lower than those for the titanium sample (Нс = 73 Oe, M*s = 7.8 × 10−3 emu/g). The discrepancy between the ferromagnetic properties of the aluminum and titanium samples correlates with the difference in the elemental composition of the pores and the presence/absence of crystallites in the pores. More pronounced ferromagnetic properties of titanium samples can be associated with the presence of crystallites in the coating pores.