OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 4 2022 0.1–0.6 µm. The average size of the structural elements is 0.3 μm. Inside the fragments of the main b-phase, nanoparticles of the w-phase are observed (Fig. 4, d). It should be noted that during the combined SPD process, the plates of the martensitic a″-phase could not be detected. This is apparently due to the fact that during pressing in the temperature range of 500–400 °С, the martensitic a″-phase was transformed into the b-phase according to the mechanism α″→a→β [18–20]. It is necessary to note that the use of abc-pressing with rolling of alloy billets leads to the formation of a more dispersed UFG microstructure compared to rolling without the pressing stage. The microstructure of the Ti-42Nb-7Zr alloy in the CG recrystallized state, obtained by annealing the sample in the UFG state at a temperature 800 °С, consists of equiaxed polyhedral grains of the matrix b-phase (Fig. 4, c). The average β-grain size is 20 µm. Inside the matrix b-grains, there are ω-phase nanoparticles with an average size of 10 nm (Fig. 4, d). Figure 5 shows the X-ray diffraction patterns for the Ti-42Nb-7Zr alloy in various states. In the cast state, the phase composition is represented by a b-phase based on a solid solution of titanium and niobium (Fig. 5, a). In the quenched state (Fig. 5, b) and after rolling (Fig. 5, c), in addition to the main β-phase, there Fig. 3. TEM images of the quenched Ti-42Nb-7Zr alloy microstructure after rolling: bright field with corresponding microdiffraction patterns (a, d) and dark field (b, c) images; microdiffraction pattern identification scheme (b) a b c d Fig. 4. TEM and optical images of Ti-42Nb-7Zr UFG alloy microstructure after abc-pressing with rolling (a, b) and in the recrystallized state (c, d): bright field with the corresponding microdiffraction patterns (a, d); dark field (b); optical (c) images
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