Ti-Al alloys can suffer from a chemical decomposition on ageing around 500!C or on air cooling.
At long ageing times this results in the formation of a2 (Ti3Al) precipitates. At reduced times
or elevated temperatures, diffuse electron or neutron diffraction peaks can be observed, which
has been termed ‘short range ordering’ (SRO). Here, we present correlative transmission electron
microscopy (TEM) and atom probe tomography (APT) results showing that the reaction proceeds
through the formation of ordered Al-rich precipitate clusters. Notably, Al-Al clustering could be
observed well before the appearance of distinct precipitates in the TEM. In addition, the Vcontaining
a phase of Ti-6Al-4V formed ordered clusters much faster than in binary Ti-7Al.
This implies that the ternary addition of b stabilisers exacerbates the problem of a2 precipitate
formation in commercial dual phase titanium alloys.