  The onset and kinetics of martensitic transformations are controlled by
impurities trapped during the transformation. For the alpha to omega
transformation in Ti, ab initio methods yield the changes in both the relative
stability of and energy barrier between the phases. Using the recently
discovered transformation pathway, we study interstitial O, N, C;
substitutional Al and V; and Ti interstitials and vacancies. The resulting
microscopic picture explains the observations, specifically the suppression of
the transformation in A-70 and Ti-6Al-4V titanium alloys.
