EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

As titanium-based alloys possess interesting specific mechanical properties, they are increasingly used in aerospace industry. Additive manufacturing is able to produce complex near net shape parts reducing the raw material quantity involved. This potential is of great interest for industrial applications. Among additive manufacturing processes, Selective Laser Melting (SLM) has proven to be an attractive manufacturing route for the production of titanium alloys as Ti-6Al-4V. However, even if these new ways of elaboration offer several advantages, there is a lack of knowledge about the microstructures inherited from SLM and the microstructural evolution during post heat treatment. Consequently, this study aims to obtain a further understanding of the microstructural evolution (recovery and decomposition of martensite α’) during post heat treatment in the Ti-6Al-4V alloy elaborated by SLM. The microstructural evolutions were tracked using the synchrotron radiation facilities, the dilatometry and the electrical resistivity measurements. In addition, interrupted heating at different temperatures were conducted to observe the microstructural evolution during heating by Transmission Electron Microscopy (TEM).The phase amounts, the d-spacing and the Full width at half maximum (FWHM) variations were determined by Rietveld refinement from XRD patterns during continuous heating up to the single β-phase domain with different heating rates and elaboration strategies. The complementarity of characterization tools clearly evidenced a shift of the α’/α $\longmapsto$ β transformation kinetics toward higher temperatures as the heating rate increases. The variation in transformation kinetics will be discussed with regard to the predicted values at thermodynamic equilibrium. In addition, the combined analysis of d-spacing and FWHM has shown the deviations from linearity at intermediate and high temperatures, which amplitude depends on the heating and elaboration conditions. These variations will be analyzed in regard of internal stress relaxation or changes of chemical composition.