The morphological features of the oxide layer formed on the Ti–15Mo alloy at various treatment temperatures and periods of time point out its growth pattern. During TO, when the Ti–15Mo alloy comes in to contact with oxygen, nucleation of the oxide occurs throughout its surface while the growth stage is governed by formation of a thin oxide scale followed by its agglomeration that eventually covers the entire surface. The oxide scales are smooth for samples oxidized at a lower temperature (500◦C) and for a lower treatment time (8 h) whereas they become relatively rough at higher temperatures (650 and 800◦C) and for longer periods of time(16 and 24 h). According to Garcia-Alonso et al. [38], the surface of Ti–6Al–4V alloy was fully covered with oxide scales in just 1 h at 700◦C. Hence, it is clear that nucleation of the oxide grains on the entire surface of Ti–Mo alloy is likely to be the first stage of oxidation. An increase in treatment temperature and time is expected to facilitate agglomeration of the oxide grains. A considerable increase in the growth of each oxide grain (with an increase in temperature and/or time) promotes attachment to the neighboring grains, thus leading to a homogeneous surface coverage with an increase in thickness of the oxide layer. The growth of the oxide layer occurs along with the formation of an oxygen diffusion zone. An increase in treatment temperature and time is likely to promote the formation of a deeper oxygen diffusion zone with a simultaneous increase in thickness of the oxide layer [30,31].