CORROSION BEHAVIOR OF HEAT-TREATED INTERMETALLIC TITANIUM-NICKEL IN HYDROCHLORIC-ACID SOLUTIONS

Samples of 45% Ti-55% Ni alloy (Ti-Ni) were heat-treated in air at 450 degrees C, and their anodic behavior in 0.3 M, 1 M, 2 M, and 4 M hydr ochloric acid (HCl) solutions was studied. In 0.3 M HCL, heat-treated Ti;Ni was passive, and very low anodic currents were observed. In 1 M and 2 M HCl, heat-treated Ti-Ni was dissolved actively, while heat-tre ated and surface-ground Ti-Ni became passive. The effect was explained by selective oxidation of Ti-Ni and formation of a layered structure on its surface with discontinuous titanium oxide and a nickel-enriched zone underneath. The latter was dissolved in the HCL solutions, thus accelerating failure of the Ti-Ni samples. In 4 MHCl, heat-treated and heat-treated/ ground samples were dissolved readily.