A study of the interaction of oxygen with the α2 phase in the model alloy Ti–7wt%Al.

Atom Probe Tomography is used to show that the α 2 phase (Ti 3 Al) forms upon ageing Ti–7Al at 550 °C with as little as 500 wppm oxygen. Notably, it is found that oxygen consistently partitions away from the α 2 precipitates to the α matrix. The role of aluminium concentration and oxygen solubility on oxygen partitioning preference is also investigated. Based on our observations, we propose a mechanism by which oxygen encourages α 2 formation despite partitioning away from it. Furthermore, nanohardness systematically measured with respect to ageing time and oxygen concentration suggests that α 2 precipitation is not the dominant hardening mechanism during ageing. Image, graphical abstract [ABSTRACT FROM AUTHOR]