Anodic dissolution behaviour and surface texture development of cobalt under electrochemical machining conditions

The anodic dissolution of hcp-cobalt in sodium nitrate solution under near-ECM conditions was investigated in situ by using a specially designed flow channel cell. The in situ investigation was focused on current densities of 5 A/cm2 and 10 A/cm2. Cobalt dissolves actively as cobalt (II) ion with a current efficiency close to 100%. In contrast to copper, the current-voltage relation does not show an active-passive transition. The dissolution strongly depends on the crystallographic orientation of the grains. The lowest dissolution rate was observed on plains vicinal to the basal plane {0 0 0 1}. No gas evolution was observed. The surface roughness is determined by the micro roughness on the individual grains.