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

One of the most critical issues in titanium metallurgy has been and remains the impact of interstitial elements and specifically oxygen on mechanical properties of titanium alloys. In these materials, oxygen is indeed known to induce a strong hardening effect combined to a severe decrease of the elongation at fracture. This embrittlement has been interpreted, until now, as a consequence of the deformation localization initiated by the interaction between the dislocations and isolated oxygen atoms in solid solution. To prevent this ductility loss, many efforts have been made to inhibit oxygen diffusion during processing and thermal treatments of titanium alloys. On this basis, there is several key challenges in the development of new “oxygen-tolerant” titanium alloys, that could take advantage of oxygen hardening without suffering from embrittlement.
This work reports on the development of a series of ternary Ti-4.5Zr-xO α-alloys with oxygen contents up to 0.8 wt%. These materials are shown to present nano-precipitates with a Ti6O-structure resulting from local ordering of oxygen in octahedral interstitial sites. Although this structure existence had been predicted by ab initio calculations, these precipitates are here observed for the first time in structural alloys and with such low oxygen contents. This work highlights that the mechanical properties associated with this microstructure in Ti-Zr-O alloys, exhibit unprecedented combination of mechanical strength and ductility, reaching over 1000 MPa and 25% respectively.
During this talk, evidence of oxygen ordering in Ti-Zr-O alloys are exposed by means of several characterization techniques: Transmission Electron Microscopy (TEM) observations and X-Ray Diffraction (XRD) analyses. The influence of the oxygen content on the precipitates size and structure will then be investigated. The consequence of this microstructure on the mechanical properties will subsequently be showed and discussed. Finally, the different perspectives and questions raised by these findings will be considered.