Corrosion of Composite Ferro-Niobium Layers in Cobalt Matrix

Résumé

The ferro-niobium composite layers in cobalt matrix were obtained by cathode depositing from electrolyte solutions on steel base. The electrolyte included in its composition cobalt sulphate and cobalt chloride, boric acid was also added for pH stabilization. The ferro-niobium, powder with granulation smaller than 5 μm, niobium content of 98% and 2% iron, were introduced into the electrolyte with 20 g/L concentration. Electrodepositing was performed at different current densities: 615 A/m², 570 A/m², 458 A/m² and the result was layers of cobalt and composite from ferro-niobium particles in cobalt matrix, with thickness varying between 50-90 μm. Corrosion resistance was assessed by linear voltammetry test watching the corrosion behavior depending on composition and structure of deposited layers. The potentiodynamic polarization curve was analysed for composite layers compared with cobalt layers. From Tafel curves was determinated the corrosion rate for each type of coatings.