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 beta-phase, within which martensitic alpha' plates are formed. The high-temperature synchrotron X-ray diffraction technique was used to show the evolution of alpha' -> alpha + beta + alpha'' transformations in Ti-6Al-4V and Ti-5Al-3Mo-V titanium alloys, which causes an increase in the content of residual beta-phase and the formation of orthorhombic alpha''-phase. The decomposition of the alpha'-phase in Ti-6Al-4V and Ti-5Al-3Mo-V samples starts at temperatures of 600 and 400 degrees C, respectively. Intensive oxidation of titanium alloys in a high-temperature chamber at temperatures above 900 degrees C resulted in a decrease in the volume fractions of beta- and alpha''-phases, as well as in the inhibition of the polymorphic alpha -> beta transformation.