Influence of oxygen ingress on fine scale precipitation of α-Ti during oxidation of Beta21S β-Ti alloy

The formation of a surface oxide layer along with α precipitation in the subsurface oxygen-enriched zone, during the oxidation of a β-Ti alloy, has been investigated using scanning electron microscopy, electron probe micro analysis, X-ray diffraction, (Scanning) transmission electron microscopy, 3D-Atom Probe studies, and nano-indentation. Immediately below the nanocrystalline oxide layer, a two-phase mixture consisting of nanoscale equiaxed α grains and rutile grains are formed. With increasing depth, the α morphology below the oxide layer varied from nanoscale equiaxed to lathlike, coupled with substantial changes in size-scale and nucleation density of α precipitates. A distinct change in the lattice parameters of α and β phases below the oxide layer and the overall micro hardness of the material is also noted. The role of oxygen ingress on the scale and morphology of α precipitation has been discussed.