Hydrogen evolution and its effects on cold rolling behavior in commercial pure titanium

The microstructural evolution induced by hydrogen in the commercially pure Ti50A and its effect on the deformation mechanisms during symmetrical cold rolling have been investigated by means of X-ray diffraction, scanning electron microscopy equipped with electron backscatter diffraction and transmission electronic microscopy. Upon charging by electrolytic method, both δ-TiHx and ε-TiH2 titanium hydrides were found to precipitate in the grain boundaries as well as within the α-phase matrix. In addition to the refinement of the microstructure, microstructural analyses of the cold rolled samples highlighted the formation of {101̅2}⟨1̅011⟩ tension twins and {112̅2}⟨112̅3̅⟩ compression twins in the hydrogenated samples rather than the {112̅1}⟨1̅1̅26⟩ tension twins usually activated in the hydrogen-free Ti50A. No evidence of correlation between the hydrides and twin formations could be detected however measurements of the local lattice curvature and strain gradients from EBSD analyses revealed a larger density of the geometrically necessary dislocations in the hydrogenated samples that could be attributed to the presence of hydrides and hydrogen dissolved in the solid solution α-phase.