Thermodynamic Analysis of the Corrosion Behaviour of Hardfacing Alloys Containing Chromium Nitrides

Chromium nitrides such as CrN and Cr₂N are often used for corrosion and wear resistant applications. In order to understand the thermodynamic stability of the nitrides, Pourbaix diagrams will be extremely useful. In this paper, Pourbaix diagrams are constructed for CrN and Cr₂N using thermodynamical data for species at 298 K (25 °C) and at a concentration of 10⁻⁶ M for aqueous species. These diagrams are useful indicators for the stable regions in which these compounds can be used. The diagrams show that passive Cr₂O₃ films form on the surfaces where chromium nitride was present. It is argued that the formation of Cr₂O₃ films will degrade chromium nitride and make it much less useful as a wear resistant layer. However, the presence of nitrogen in solid solution is better for the stability of passive films.