The effect of nitrogen on the passivation mechanisms and electronic properties of chromium oxide layers

In this work, several Physical Vapour Deposition (PVD) films of chromium and chromium nitride were grown by adjusting the nitrogen flow rate. It was found that films containing lower nitrogen content exhibited better corrosion behaviour in relation to their microstructure. Moreover, the resistivities of the samples were found to increase with N content due to a decrease in the number of metallic bonds in the coatings and a loss of oxide layer conductivity. The latter is linked to a decrease of charge carrier density by the incorporation of NH4+ species into the passive layers, which decreases cation vacancy density.

Research highlights► Nitrogen effect on the passive film functionalizing. ► Contribution of Corrosion Science for material design. ► Lower amount of N is preferable to better corrosion resistance behaviour. ► Higher content of nitrogen leads to a decrease of the passive layer conductivity due to the occupation of cation vacancies (VCr2-,VCr3-) by NH4+ species.