CORROSION RESISTANCE OF COBALT AMORPHOUS ALLOYS IN SODIUM CHLORIDE SOLUTION

O. Hertsyk, M. Kovbuz, R. Тemitska, N. Pandiak, М. Таshak


DOI: http://dx.doi.org/10.30970/vch.6401.331

Abstract


Cobalt-based ribbon amorphous metal alloys (AMА) are used as soft magnetic materials in serial production of television equipment and instrument manufacturing. As materials with high strength and hardness at elevated temperatures and also durable in aggressive environments, cobalt alloys are used for cutting tools operating in aggressive chemical environments.

The ribbon amorphous metal alloys Co73,5Fe4,2Si6,0B16,3 (АМА-1), Co73,2Fe4,3Mn0,5Si5,3B16,7 (АМА-2) та Co73,3(Fe, Ni, Mo, Mn)5,7(Si0,2B0,8)21 (АМА-3) were studied using chronopotentiometry and cyclic voltammetry.

Amorphous alloys based on Co show high corrosion resistance in various aggressive environments. The values of potential determined by potentiometric measurements confirm the lower corrosion resistance of the outer surface of cobalt AMА electrodes compared to the contact surface. The change in the potential of the contact and outer surface of all AMА is non-linear, which implies the competitiveness of the processes of the formation of oxide layers and their dissolution at different concentrations of NaCl aqueous solutions. In all cases, with an increase in the concentration of sodium chloride from 0.125 to 1.0 M, the value of the potential shifts to the cathode side. The additions of almost all metallic elements to amorphous alloys of the metal-metalloid type improve their corrosion resistance. Based on the electrochemical parameters, it can be concluded that at the initial moment of contact with a 0.5 M aqueous solution of sodium chloride, the alloy Co73.3(Fe, Ni, Mo, Mn)5.7(Si0.2B0.8)21 has the highest corrosion resistance. However, under the conditions of multiple cyclic changes of potential in an aggressive media, the corrosion potentials shift to the cathodic side, and the corrosion currents increase for all investigated AMАs,. Moreover, the greatest shift in the corrosion potentials of both the contact and external surfaces is observed for the multicomponent cobalt alloy. According to the results of elemental analysis and microphotograph of the surface, it was established that in all aggressive media, a primary oxide film is preserved, which has some defects promoting the growth of thicker oxide-hydroxy layers.

 

Keywords: amorphous metallic alloys, cobalt, corrosion resistance.


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