Corrosion resistance properties of plasma nitrided Ti-6Al-4V alloy in nitric acid solutions

The corrosion resistance of plasma nitrided Ti–6Al–4V titanium alloy in nitric acid solutions was investigated using polarisation curves, cyclic voltammetry, XRD analysis and surface microhardness. For comparison, untreated alloy samples were tested under the same conditions. While the untreated alloy shows a passive behaviour, the compound layer obtained by glow-discharge nitriding treatment, which is composed of an outer TiN and an inner Ti2N layer, shows a high electrochemical inertia; however, if the polarisation potential is higher than a threshold or the period of immersion in high oxidising acid solution is sufficiently long, then the compound surface layer will be attacked and removed with corrosion rate higher than in the case of the untreated Ti–6Al–4V alloy. The corrosion resistance of Ti2N layer results higher in comparison with that of TiN layer.