Acicular α2 precipitation induced by capillarity at α/β phase boundaries in Ti–14Al–2Zr–3Sn–3Mo–0.5Si titanium alloy

Abstract The precipitation of α2 phase based on Ti3Al from Ti–14Al–2Zr–3Sn–3Mo–0.5Si titanium alloy homogenized at different temperatures in the (α+β) two-phase field has been characterized. Minimal lattice mismatch between the α and α2 phase leads to a massive ordering transformation upon cooling and results in morphologies distinct from the ellipsoidal shape of the α2 particles. Enrichment of Al in front of growing β grains due to the Gibbs–Thomson effect, together with preferential diffusion of Al along 1 1 2 0 produces a layer of acicular α2 particles apparently perpendicular to the α/β phase boundaries. Removal of the capillarity-induced composition inhomogeneity by subsequent aging at 750 °C results in disappearance of the acicular shape of the α2 particles.