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The α+β titanium alloy Ti-6Al-4V having different structure and phase composition is investigated in this paper under the tensile deformation in the temperature range from 773 to 1223 K. The transmission and scanning electron microscopy observations show that superplastic deformation of the Ti-6Al-4V alloy with the ultra-fine grain structure produces the formation of the secondary phase particles along the grain boundaries. It is identified that this process is connected with the vanadium redistribution during deformation. The obtained temperature dependence of the fracture elongation of the alloy samples is nonmonotonic and exceeds 700% at 973 K. It is supposed that the reduction in the fracture elongation within 1073–1173 K range is associated with the deformation-induced micron-sized grains and the formation of lamellar β- and α″-phases along the grain boundaries.

The effect of annealing at 673 K for 6–24 h on the structural and phase state and mechanical properties of the titanium alloy of a Ti-Al-V system that was previously subjected to severe plastic deformation by uniform compression deformation, has been studied. It has been established that these annealings lead to a nonmontonic dependence of the mechanical properties of the alloy on the annealing time. It has been shown that the annealing of the Ti-Al-V alloy in a submicrocrystalline state is accompanied by simultaneous hardening processes, i.e., the formation of fine particles during phase transformations and the formation of new nanosized grains, and softening processes, i.e., recovery processes and the growth grains to micron sizes. The prevalence of a given process during annealing determines the deterioration or improvement of the alloy’s mechanical properties.

The special features of the ultrafine-grained structure forming in a Ti-6Al-4V alloy with the use of a method combining severe plastic deformation and reversible hydrogen treatment are studied by electron microscopy and X-ray diffraction analysis. Martensite and the α ↔ β phase transformations due to hydrogen presence are found to promote structure refining during severe plastic deformation of the alloy. This makes it possible to decrease the degree of deformation required for obtaining the ultrafine-grained structure with the size of elements of 0.1–0.5 μm. Formation of the ultrafine-grained structure in a Ti-6Al-4V alloy is shown to lead to growth of its strength properties by approximately a factor of 1.5, an increase in the hydrogen embrittlement resistance, and a decrease in the temperature transition to the superplastic state by 200–300 K.

The special features of the evolution of the structural and phase states of a Ti-6Al-4V alloy in forming submicrocrystalline structure with the use of temporary hydrogen treatment are studied by electron microscopy and x-ray diffraction analysis. Plastic deformation in the α + β two-phase region at 1023 K is found to initiate a complete β → α transformation in a Ti-6Al-4V-H alloy to form an α phase with lattice parameters different from those of the equilibrium α phase. Isothermal annealing at a dehydrogenation temperature of 873 K gives rise to α + β two-phase submicrocrystalline structure with a grain size of ∼ 0.3 µm. The use of nonequilibrium hydrogen release in the deformed Ti-6Al-4V-H alloy exposed to electron beams is shown to result in one-phase submicrocrystalline structure and grain refining. Possible reasons underlying the phase transformations in the alloy under study are discussed.