O. N. Lykova

Structure and mechanical properties of ultrafine-grained Ti-6Al-4V alloy made by applying reversible hydrogen alloying

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.

Influence of low-temperature annealing time on the evolution of the structure and mechanical properties of a titanium Ti-Al-V alloy in the submicrocrystalline state

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.

Influence of heat treatment parameters on the structure and mechanical properties of a titanium VT6 alloy in the submicrocrystalline state

The effect of additional annealing on the structure and mechanical properties of the titanium VT6 alloy in the submicrocrystalline state is studied. It is shown that the annealing at 833 K for 20 min does not significantly affect the mechanically properties of the alloy at room temperature. However, this annealing severely deteriorates the superplastic properties of the alloy. Annealing at 873 K for 5 min results in a sharp decrease in the strength properties of the alloy at room temperature (by about 20%). Nevertheless, the superplastic properties of the alloy after this annealing are the highest ones among those considered in this work. It is assumed that the state of grain boundaries plays the decisive role in the development of the superplastic flow of the VT6 alloy after three-dimensional pressing and subsequent annealing.