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

Among the various significant questions affecting titanium metallurgy, the effect of interstitials, more specifically oxygen, on the (mechanical) properties of titanium alloys remains one of the most critical issues. For decades, oxygen has been considered as a detrimental element, leading to drastic embrittlement. However, there is still an important lack of knowledge on underlying mechanisms regarding this effect.

In this work, a series of Ti-O alloys displaying high oxygen concentration (between 0.4 and 1wt%) has been carefully investigated to address more specifically this question. A particular attention is paid to the process route, which is supposed to play a role. Two different aspects are of great interest: (1) the determination of the atomic scale structure of Ti-O alloys, as a function of the chemical composition, with special attention to possible local ordering or local oxygen-driven structural modification. (2) The impact of oxygen content on: (a) the macroscopical properties (resistance/ductility trade-off) and: (b) the operative deformation mechanisms, at room temperature.

Ti-O specimen with different controlled oxygen concentrations were fabricated by arc-melting and were investigated by DRX, EBSD and TEM analysis, at different stages of the process route but in particularly under their fully recrystallized microstructural state. The mechanical properties have been studied by tensile tests in quasi-static conditions. It was shown that this series of newly developped Ti-O alloys displayed a spectacular combination of tensile strength and ductility with a small drop of ductility with increasing oxygen content, in particular.

In this talk, the origin of these peculiar mechanical properties will be extensively discussed, based on new microstructural insights at the nano-scale, regarding more particularly local oxygen ordering in the alpha titanium matrix. The effect of the process leading to the strength-ductility trade-off will also be discussed. The larger perspectives opened by these new findings will then be described and discussed.