HAADF-STEM study of phase separation and the subsequent α phase precipitation in a β-Ti alloy

The α phase precipitation via phase separation (β → β′ + β) in the Ti–25Nb–3Mo–3Zr–2Sn (wt.%) alloy has been studied by scanning transmission electron microscopy. The observations clearly show that α phase nucleates at the β/β′ interface and grows into the β′ phase by ledges. To accommodate the precipitation of α phase, the β′ phase undergoes both morphological and structural changes. The crystallographic relationships between the contiguous α, β′ and β phases are identified from the atomic-scale images and are compared with those calculated from the crystallographic models.