On the Repassivation Behavior of High‐Purity Titanium and Selected α, β, and β + α Titanium Alloys in Aqueous Chloride Solutions

Abstract

The repassivation characteristics of a titanium thin film evaporated from a high‐purity Ti source as well as selected α (commercially pure Ti, Ti‐5Al‐2.5Sn), β, and β + α titanium alloys (Ti‐15Mo‐3Nb‐3Al, Ti‐15V‐3Cr‐3Al‐3Sn, and Ti‐3Al‐8V‐6Cr‐4Zr‐4Mo) were examined. Both the rapid thin film fracture and scratch depassivation methods were used in aqueous chloride solutions (0.6 M NaCl, 5 M HCl, 5 M LiCl, 5 M HCl + 1 M ). Bare surface open‐circuit potentials followed the relationship (pH = 0) − 0.043 pH based on the mixed potential established between the anodic , and water or reduction reactions. Oxide formation after depassivation was of low overall current efficiency on all titanium materials; a large percentage of the anodic charge following depassivation contributed to dissolution. Consequently, an empirical expression was used to describe the anodic current density decay during repassivation; . Potentiostatic current transients on rapidly fractured thin film Ti produced plateau bare‐metal io values greater than 100 A/cm2 which were below the theoretical ohmic limit, m = 1.0 to 1.4 depending on solution and potential and to values from 20 to 30 μs. Two anodic Tafel regions and a single cathodic region best described IR‐corrected E — log i relationships for bare Ti in all electrolytes. LiCl and inhibited bare surface dissolution but slightly delayed current density decay. Minimal differences between any of the repassivation parameters utilized were observed for selected α, β, and β + α titanium alloys. The similarity was attributed to dominance of production in the total anodic charge during repassivation and predominantly formation in the passivating oxides of all alloys.