The corrosion behaviour of sputter-deposited amorphous Mn-Ti alloys in 0.5 M NaCl solutions

Amorphous Mn-Ti alloys were successfully prepared by DC magnetron sputter-deposition in a wide composition range. Corrosion experiments and anodic potentiodynamic polarization measurements performed in 0.5 M NaCl at pH 5.5 and 11.5, open to air at 30 degrees C, show improved the corrosion resistance of the alloys compared with manganese. Alloying of 12 at.% or more titanium to manganese was very effective in increasing the corrosion resistance in aerated alkaline solution containing chloride ions. X-ray photo-electron spectroscopic analysis of spontaneously passivated films formed in alkaline medium revealed that titanium ions were enriched in the passive films. The passive films formed on Mn-Ti alloys at pH 11.5 were composed of a homogeneous double oxyhydoxide of tetravalent titanium and divalent manganese. It is concluded that the presence of oxidized manganese and titanium in the form of a homogeneous double oxyhydroxide is responsible for the corrosion resistance of the Mn-Ti alloys. (C) 1997 Elsevier Science Ltd.