In this study, the influence of oxygen diffusion on the physical properties of Ti–6Al–2Sn–4Zr–2Mo–0.1Si was examined. Measurements were carried out directly on sample cross sections which were preoxidized at high temperature. The lattice parameter evolution was measured using synchrotron X‐ray diffraction and was coupled with microhardness and electron probe microanalyzer results with the aim of highlighting their relationships. The results show that the hardness and oxygen gradients along the oxygen diffusion zone in the alloy are similar to the evolution of the α‐phase unit‐cell volume quantified by X‐ray diffraction. Linear relationships were found between these three parameters.

In this study, the effect of oxygen diffusion on the crystallographic evolution of α-titanium has been studied using synchrotron X-ray diffraction. Measurements were carried out directly on sample cross-sections that were directly pre-oxidized at high temperature. Changes in hardness, oxygen content and lattice parameters after oxidation were determined by coupling microhardness measurements and electron probe microanalyzer results. IntroductionTitanium and its alloys are widely used in a variety of applications, including the aerospace and chemical industries. This widespread use is because of titanium's mechanical properties, low density and good corrosion resistance. Presently, aerospace manufacturers try to reduce weight, while increasing engine efficiency, often by exposing different components made of Ti-base alloys to higher temperatures. The effect of oxidation on the mechanical properties must therefore be taken into account.The O-Ti (oxygen-titanium) system and the oxidation of titanium have been extensively studied, but few correlations between oxygen concentration and α-titanium crystallographic modifications exist [1,2]. At temperatures above 600-700°C, the oxidation rate is parabolic; it then becomes linear with increasing temperature. This oxidation leads to the formation of an oxide layer (OL) on the surface with an oxygen diffusion zone (ODZ) in the metal. In this temperature range, TiO 2 rutile, an n-type semiconductor, has been observed to form an OL on pure titanium during oxidation [1,3]. The oxide that is initially formed is compact, but after extended exposure, multiple OLs are observed and can be associated with oxide spallation [6]. Even during the parabolic stage, the oxidation mechanism of titanium is complex owing to the high solubility of oxygen in the hexagonal-close-packed (hcp) structure of α-titanium (up to 30 at.%). During oxidation, oxygen diffusion and dissolution under the OL lead to development of the ODZ. This solid solution is harder and more brittle than the initial metal [4,5]. The depth of the ODZ increases with increasing temperature and duration of exposure. Understanding the oxidation mechanism of titanium requires a study of both OL growth and dissolution, as well as diffusion of oxygen in titanium (ODZ growth).