An assessment of the instability of Ti and its alloys in acidic environments at elevated temperature

The effect of temperature in the range from 20 to 100 °C on the corrosion activity of Ti alloys in three different solutions [HCl of pH=4, (HCl + 500 ppm NaCl) of pH=4 and HCl of pH=2] was studied by DC electrochemical testing methods. Potentiostatic tests and measurement of the free corrosion potential (E_corr) were employed, in conjunction with microscopical analysis, to investigate the localised instability of four materials. It was found that pitting is the main localised corrosion type for commercially pure (CP) Ti and Ti alloys in HCl. A critical pitting temperature (CPT) was defined for the different materials. Observation of the passive current transients before the CPT is reached indicate that corrosion `events' occur throughout the increasing temperature phase and that these `events' are dependent on the material and environment.