## 3 Results and Discussion
### Microstructure Characterization after TMT  
#### 3.2.1 Scanning Electron Microscopy  
The EBSD images shown in Figure 4 demonstrate the alloy microstructures after \(0.3+600\) (30), \(0.3+800\) (30), \(1.5+600\) (30), \(1.5+800\) (30), and \(3.0+600\) (30) TMTs. In all alloys, after \(0.3+600\) (30), a \"plate\" structure within the grain body of the \(\beta\)-phase is observed. This microstructure feature is a result of \(\{332\}\)\(<\)\(113\)\(>\) twinning during CR, which has been extensively studied for various metastable titanium alloys. The extent of cold plastic deformation greatly influences its contribution to microstructure formation [37; 38; 39; 40]. Subsequent PDA at 600 \({}^{\circ}\)C does not eliminate the twinning structure through static recrystallization. Only in the 18-15 alloy is the formation of new \(\beta\)-phase grains with a size of 2-10 \(\upmu\)m locally observed (see Figure 4b), indicating a partial recrystallization. The twinned structures of the 22-6 and 41-12 alloys remain preserved and are more resistant to recrystallization during PDA at 600 \({}^{\circ}\)C (see Figure 4a,c). The extent of cold plastic deformation greatly influences its contribution to microstructure formation (see Figure 4a). Figure 3: Changes in the lattice parameter \(a_{\beta}\) (a) and \([211]_{\beta}\) FWHM B (b) of \(\beta\)-phase of 22-6, 18-15, and 41-12 alloys after \(0.3+600\) (30), \(0.3+800\) (30), \(1.5+600\) (30), \(1.5+800\) (30), \(3.0+550\) (5), \(3.0+600\) (5), and \(3.0+600\) (30). Figure 4: Orientation distribution maps (EBSD images) of 22-6 (**a**,**d**,**g**,**j**,**m**), 18-15 (**b**,**e**,**h**,**k**,**n**), and 41-12 (**c**,**f**,**i**,**l**,**o**) alloys after 0.3 + 600 (30) (**a**–**c**), 0.3 + 800 (30) (**d**–**f**), 1.5 + 600 (30) (**g**–**i**), 1.5 + 800 (30) (**j**–**l**), and 3.0 + 600 (30) (**m**–**o**). Black lines correspond to high-angle boundaries (\(\geq\)15\({}^{\circ}\)); white lines correspond to low-angle boundaries (\(<\)15\({}^{\circ}\)). Increasing the PDA temperature to 800 \({}^{\circ}\)C leads to the development of recrystallization and grain growth in all alloys (Figure 4d-f). However, in the 18-15 and 41-12 alloys, the grains are elongated in the rolling direction, indicating the development of recrystallization through the predominantly directed movement of high-angle boundaries. A similar phenomenon was previously observed in the 18-15 alloy as a result of annealing after hot rotary forging [41] This phenomenon deserves a separate study. TMT including 1.5 + 600 (30) leads to the formation of a mixed partially recrystallized microstructure of the \(\beta\)-phase characterized by a combination of smaller equiaxed recrystallized grains with non-recrystallized areas which presumably contain a polygonized dislocation substructure, i.e., subgrains separated by low-angle boundaries (Figure 4g-i). After PDA at 800 \({}^{\circ}\)C, predominantly recrystallized grains are observed. It should be noted that the size of the structure elements increases with the transition from low- to high-Zr alloys; however, there are non-recrystallized areas in the alloys (Figure 4j-l). The use of 3.0 + 600 (30) TMT leads to significant grain refinement in all alloys (Figure 4m-o). Based on the EBSD maps, the histograms of grain size distribution were plotted (Figure 5). For microstructures containing elongated structure elements, grain sizes were measured in two directions: the rolling direction and the transverse direction. For equiaxed grains, these values were equal within the error limits, and only one value of the grain size is given as an average of the values in two directions. Almost all grain size D distribution histograms for the 22-6, 18-15, and 41-12 alloys closely resemble the log-normal distribution, with a bias towards the smaller grains. This bias is a result of the recrystallization process, when a number of new smaller grains occupy the large, deformed areas.