Influence of Aluminum and Vanadium on the Anodic Dissolution of Ti-Al and Ti-V Binary Alloys in Concentrated Hydrochloric Acid

To understand the combined roles of Al and V in the dissolution-passivation mechanism of the ternary T A₆ V alloy in hydrochloric acid, the roles of Al and V were investigated separately in Ti-Al and Ti-V binary alloys. The study was based on: (1) the analysis of stationary polarization curves, according to a model previously established for Ti dissolution; (2) the interpretation of corrosion morphology; and (3) the identification by x-ray diffraction of the products formed at the electrode. It was evidenced that the primary role of V and Al, as alloying elements in the active dissolution of titanium, is to modify the potential range at which Ti H₂ forms. The outstanding influence of hydride on the dissolution kinetics has already been established. Vanadium completely impedes its formation, whereas aluminum shortens its existent potential range, but activates its formation. One consequence of these effects of Ti H₂ is that the three rate-determining reactions in active dissolution are inhibited by vanadium, whereas two are activated and the third inhibited by aluminum. In passive dissolution, the efficiency of the passivating layer is reduced by aluminum and increased by vanadium.