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

The alpha phase precipitation via phase separation (beta -> beta ' + beta) in the Ti-25Nb-3Mo-3Zr-2Sn (wt.%) alloy has been studied by scanning transmission electron microscopy. The observations clearly show that a phase nucleates at the beta,beta ' interface and grows into the beta ' phase by ledges. To accommodate the precipitation of alpha phase, the beta ' phase undergoes both morphological and structural changes. The crystallographic relationships between the contiguous alpha,beta ' and beta phases are identified from the atomic-scale images and are compared with those calculated from the crystallographic models. (C) 2015 Elsevier Ltd. All rights reserved.