Application of surface response analysis to the optimisation of nitric passivation of cp titanium and Ti6Al4V

Passivation of Ti6Al4V and cp Ti by mean of nitric acid treatment are used to reduce their surface reactivity, and consequently increasing resistance to corrosion, in physiological media.In this work, the response surface methodology was employed to know the effects of operating parameters of the nitric passivation (HNO3 content, temperature of solution and passivation period) on the corrosion resistance of commercially pure (cp) titanium and Ti6Al4V alloy in Ringer's solution. The experiment included two 33 factorial designs. According to the responses from the experimental designs, the effects of each variable were calculated and the interactions between them were determined. The statistical test has revealed that the main effect of the nitric acid content is the most significant factor. The surface response methodology was applied to graphically determine the optimal working conditions.Different electrochemical techniques (OCP, Rp and cyclic polarisation tests) were used to compare the electrochemical behaviour of cp Ti and Ti6Al4V, with and without passivation.