Corrosion resistance of amorphous cobalt alloys in acetic acid solutions

Abstract

Corrosion resistance of ribbon amorphous alloys based on cobalt in acetic acid solutions of different concentrations was investigated by various physicochemical methods. An increase in corrosion resistance with an increase in acid concentration due to the formation of dense passivation layers on the surfaces was established. Most amorphous cobalt-based alloys are characterized by high strength and impact toughness, corrosion resistance, and high magnetic permeability. Amorphous metal alloys (AMА) based on Co, which are characterized by unique physicochemical properties, are used in the medical field, in particular, to create dental and bone implants. The study of their corrosion resistance in aggressive environments of organic acids makes it possible to choose amorphous alloys that will be more effective in this field. A potentiometric study of changes in the corrosion resistance of AMА Co73,2Fe4,8Si5,3B16,7 in aqueous solutions of acetic acid of different concentrations showed a higher durability of the alloy of this composition in acid solutions, compared to the sodium chloride solution, which is a standard for corrosion assessment. High durability is also confirmed by a small difference between the initial and final potential values. With an increase in acid concentration, the final potential values slightly shift to the anodic side, which reflects an increase in corrosion resistance. Similar potentiometric studies of AMА Co73,2Fe4,3Mn0,5Si5,3B16,7, which contains Mn, in aqueous solutions of acetic acid also confirmed the increase in durability with increasing acid concentration, which is obviously related to the formation of dense passivation layers under such conditions. The study of the corrosion resistance of AMА in aqueous solutions of acetic acid by the method of cyclic voltammetry, i.e. with additional loading of samples by cyclic scanning of the potential, showed that with an increase in the duration of contact with an aggressive environment under these conditions, a shift in the values of the corrosion potentials of both contact and external surfaces in the cathodic direction is observed and the growth of corrosion currents, which indicates a decrease in the corrosion durability of the samples. The contact surface is also characterized by higher corrosion resistance under such conditions. As the concentration of acetic acid increases, the durability of the samples increases, even under conditions of cyclic polarization of the samples. Based on the electrochemical parameters, it was found that the corrosion resistance increased with increasing acid concentration, apparently due to the formation of dense passivation layers on the surfaces. Microphotographs of surfaces and their elemental composition after contact with (0.01–1.0) M aqueous solutions of acetic acid confirmed the high durability of alloys of this composition in such aggressive environments.