Electrochemical Properties of Nitrided Ferrous Materials

Abstract

Results of electrochemical and X-ray studies of pure iron and iron based alloys nitrided in an NH₃-H₂ atmosphere at 550°C are presented. Structural peculiarities of the nitrided layers are related to the solubility of some alloying elements, especially chromium, in iron nitrides. Current density-potential curves recorded on oblique sections at various ‘depths’ in 0.025M H₂SO₄ + 0.05M Na₂SO₄ aqueous solutions show, in principle, a distinct tendency to passivation of 8 compound layers. Significant changes in the electrochemical behaviour of iron-chromium alloys containing ∼6.5 and ∼13%Cr, as characterised by active anodic dissolution, were observed in the precipitation zone. A potential reversal on nitrided surfaces due to oxygen coverage and some effect of soluble alloying elements on the electrochemical behaviour of the 8 phase were also found.