Influence of reversible hydrogen alloying on nanostructure formation in titanium alloys subjected to severe plastic deformation

The method for production of a structure with a grain size of 30-40 nm in two-phase titanium alloys is proposed. It is shown. that the nanostructure can be formed in billets of 150x70x15 mm, and sheets of 250x 150x1 mm. The method consists of several steps including hydrogen alloying of the alloy; heat treatment, warm deformation and finally dehydrogenating vacuum annealing. alpha-, alpha+beta and beta-titanium alloys have been investigated. Hydrogen content varied in the rank 0.1-30 at. %. Microstructure was examined using optical. scanning, transmission electron microscopy and X-ray analysis after every step of the treatment. The investigations have shown that a specific character of phase transformations in hydrogenated titanium alloys plays a leading role in formation of nanostructure. The effect of dissolved hydrogen on dynamic recrystallization in alpha- and beta- phases is of a secondary importance. Additional refinement in structure is observed in the deformed alloys after vacuum annealing, if its temperature is less than the temperature of their deformation. The work was focused on the optimization of hydrogen content and deformation conditions with the aim to create the nanostructure in titanium alloys and to enhance their mechanical properties.