Corrosion resistance of molybdenum-containing titanium alloy for overpack in simulating underground environment

Crevice corrosion behavior of titanium (Ti) and binary Ti alloys containing 5–25 mass% of molybdenum (Mo) was investigated in 10% NaCl at 100 °C. Although a considerably large shift in crevice potential toward the active region and large current were observed with Ti, no change in crevice potential or current was observed with the Mo–Ti alloy. The resistance against crevice attack was found to depend on the Mo content of the alloys in the experiment. Further investigations by potentiodynamic polarization and the electrochemical impedance spectroscopy (EIS) method were conducted. Polarization measurements showed an increase in cathodic current density with the increase of Mo content in Ti alloys. As the Mo content was increased to around 10%, the corrosion potential was found to exist within the passive region even in highly acidic solutions. These results illustrated the more highly passivating behavior of 10–25% Mo–Ti alloys than pure Ti and 5% Mo–Ti alloys. The higher impedance values shown by EIS revealed the high ability of 15% and 25% Mo–Ti alloys to keep the passive film even in the acidic solutions. It was found that Mo–Ti alloy could keep the passive film even in a high chloride concentration environment at 100 °C. Hence, as for the crevice corrosion, this alloy could be useful for environments simulating the overpack near the coast.