Thermodynamic Basis of Non-equilibrium Phase Transformations of bcc β-Phase in Ti–Mo System

Abstract

This study reports the experimental identification of transformation products of high temperature bcc β phase in Ti–xMo (x = 1, 7, 15, 25 wt%) alloys and aims to understand the transformations by thermodynamic modelling. The high temperature bcc β phase had undergone martensitic transformation in Ti–1Mo and Ti–7Mo alloys, resulting in acicular martensitic structure within large β grains. X-ray diffraction (XRD) analysis confirmed the martensite to be hcp (α′) and orthorhombic (α″) in Ti–1Mo and Ti–7Mo alloys respectively. Combined analysis of XRD and transmission electron microscopy (TEM) suggested the formation of fine plates of α″, omega (ω) and bcc β phases in Ti-15 and Ti-25 Mo alloys. Calculation of enthalpy of formation supported the stability of solid solution phase over the amorphous phase in the entire concentration range of Mo.