Mechanism of the oxidation of titanium and the alloy TA6V4 by water vapour

During the oxidation of pure titanium and of Ti-6Al-4V alloy by water vapour, in the temperature range 700-9000C, recrystallisation of the outer part of the oxidised layer was observed. It was previously suggested that the mechanism involved is identical with that described by Kofstad for the oxidation of titanium in oxygen at higher temperatures (> 9000C). Various experiments on pure titanium at lower temperature (< 9000C) (oxidation by oxygen-water vapour mixtures, or oxidation by oxygen and water vapour of preoxidised samples) seem to support this suggestion. The results can be interpreted by assuming the formation of hydroxide ions (OH-) in the outer part of the oxidised layer. (Auth.)