Electrochemistry and Passivity of a Ti‐15Mo‐3Nb‐3Al Beta‐Titanium Alloy in Ambient Temperature Aqueous Chloride Solutions

To understand the effect of Mo‐Nb additions on the electrochemical behavior of β‐titanium alloys in ambient temperature chloride solutions, characterization of the electrochemistry and passivity of a Ti‐15Mo‐3Nb‐3Al alloy (β‐21S) was undertaken. Both solution heat‐treated (SHT) and peak‐aged (PA) alloys exhibited passive anodic behavior in aerated and deaerated 0.6 M NaCl , aerated and deaerated 0.6 M NaCl adjusted to pH 1 with HCl , as well as aerated 5 M HCl . X‐ray photoelectron spectroscopy (XPS) performed after exposure to neutral 0.6 M NaCl indicated that both PA and SHT β‐21S formed a predominantly TiO 2 film. Auger electron spectroscopy (AES) and cathodic kinetics suggest that the Mo and Nb alloying additions are incorporated into the oxide in amounts less than that found in the alloy. The predominance of the passivating TiO 2 may explain the similarity of the electrochemical behavior observed. However, in deaerated 5 M HCl , all materials displayed active‐passive behavior except for SHT β‐21S which was spontaneously passive. This result suggests that the presence of the α‐phase is deleterious to the formation of a protective passive film on PA β‐21S in deaerated 5 M HCl .