Mechanisms of Ti<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si9.svg"><mml:msub><mml:mrow /><mml:mn>3</mml:mn></mml:msub></mml:math>Al precipitation in hcp <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"><mml:mi>?</mml:mi></mml:math>-Ti

Nucleation and growth of Ti3Al ?2 ordered domains in ?-Ti–Al–X alloys were characterised using a combination transmission electron microscopy, atom probe tomography small angle X-ray scattering. Model based on Ti–7Al (wt.%) containing O, V Mo aged at 550?C for times up to 120d the resulting precipitate dispersions observed intermediate points. Precipitates grew around 30nm size, with volume fraction 6–10% depending tertiary solutes. Interstitial O was found increase equilibrium ?2, while showed relatively little influence. Addition any solutes this study, but most prominently Mo, nucleation density decrease size possibly coarsening rate. Coarsening can be described by Lifshitz-Slyozov-Wagner model, suggesting matrix diffusion-controlled mechanism (rather than control interfacial coherency). Solutionising temperature affect number an activation energy Ef=1.5±0.4 eV, supporting hypothesis that vacancy concentration affects nucleation. The observation all is also consistent vacancy-controlled mechanism.