Fe and/or Co-containing coatings on titanium: Features of plasma electrolytic formation, composition, and magnetic properties

Abstract

Fe- and/or Co-containing coatings have been formed on titanium by plasma electrolytic oxidation (PEO) in electrolytes-sols with colloidal particles of Fe(III) and/or Co(II) compounds. The influence of the electrolyte formula has been studied on the coatings' composition, surface morphology, and magnetic properties. It has been established that the total concentration of iron, cobalt, and titanium in the coating composition is 13.1–22.0 at. %, while their thickness varies from 22 to 37 μm, and the porosity ranges from 10 to 26 %. Micro- and nanosized crystal-like particles have been found both on the surface (in valleys, around pore mouths, and in caps covering pores) and inside pores (at the bottom and walls). In the particles and the layer lining the bottom of the pores, the concentration of iron, cobalt, and titanium is higher than over the surface (49.7–59.1 at. %). Depending on electrolyte formula, the crystallites located in the pores contain (at. %) 28.4–39.3 O; 3.5–9.5 P; 20.3–29.4 Ti; 2.1–7.5 W; up to 22 Fe and up to 38.8 Co. The values of the coercive force measured at 300 K vary from 6366 to 27,056 A/m, and those at 3 K range from 3581 to 17,428 A/m. The ferromagnetic properties of the coated samples correlate with the elemental composition of the particles found in the pores and on the surface.