Acicular α_2 precipitation induced by capillarity at α/β phase boundaries in Ti-14A-2Zr-3Sn-3Mo-0.5Si titanium alloy

摘要

The precipitation of α_2 phase based on Ti_3Al 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 α_2 phase leads to a massive ordering transformation upon cooling and results in morphologies distinct from the ellipsoidal shape of the α_2 particles. Enrichment of Al in front of growing β grains due to the Gibbs-Thomson effect, together with preferential diffusion of Al along produces a layer of acicular α_2 particles apparently perpendicular to the α/β phase boundaries. Removal of the capillarity-induced composition inhomogeneity by subsequent aging at 750 ℃ results in disappearance of the acicular shape of the α_2 particles.