The High-Temperature In Situ Synchrotron Study of the Structural-Phase Transformations in 3D-Printed Ti–6Al–4V and Ti–5Al–3Mo–V Titanium Alloys

An wire-feed electron beam additive manufactoring has been used to obtain the samples of Ti‒6Al–4V and Ti–5Al–3Mo–V titanium alloys. Optical, scanning and transmission electron microscopies have been used to show that the microstructure of the 3D printed samples of Ti–6Al–4V and Ti–5Al–3Mo–V alloys consists of columnar primary grains of the β-phase, within which martensitic α' plates are formed. The high-temperature synchrotron X-ray diffraction technique was used to show the evolution of α' → α + β + α'' transformations in Ti–6Al–4V and Ti–5Al–3Mo-V titanium alloys, which causes an increase in the content of residual β-phase and the formation of orthorhombic α''-phase. The decomposition of the α'-phase in Ti‒6Al–4V and Ti–5Al–3Mo–V samples starts at temperatures of 600 and 400°C, respectively. Intensive oxidation of titanium alloys in a high-temperature chamber at temperatures above 900°C resulted in a decrease in the volume fractions of β- and α''-phases, as well as in the inhibition of the polymorphic α → β transformation.