NaCl-induced accelerated oxidation of a titanium alloy

Abstract

The effect of a surface deposit of NaCl on the oxidation characteristics of a high-temperature titanium alloy was studied in the temperature range of 400–600°C. The influence of the water vapor content in the oxidizing environment was examined in the light of an existing electrochemical mechanism proposed for the hot-salt stress-corrosion-cracking phenomenon found in titanium alloys. It was established that the NaCl deposit increased the oxidation rate by a factor of 100 for hygrometry levels of 10 ppm or higher. Further, there exists a hygrometry threshold between 10 and 5×10⁻³ ppm below which the NaCl-induced accelerated oxidation decreases with decreasing hygrometry level. Electron microprobe analysis suggests that the titanium matrix reacts with chlorine before forming rutile.