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Dynamic recrystallization to a large extent determines the microstructure of near-α titanium alloys during the thermo-mechanical processing in α + β two phases zone. And the initial microstructure has a dramatic effect on the recrystallization behavior. Therefore, this paper deals with the recrystallization behavior of a near-α TA15 titanium alloy sheet with substantial prior deformed substructures during the annealing and hot tension at 800 °C. Undeformed and deformed regions of tensile samples, viz., static recrystallization and dynamic recrystallization, were studied respectively through EBSD observation. It was found that, the unusual intragranular nucleation of discontinuous recrystallization was observed in the relatively coarse grains, which was formed by the enclosed low angle grain boundaries rearranged by the thermally activated recovery. And most of the recrystallized grains manifested as three types of special grain boundaries, namely [0001]30°, 11 2 ¯ 0 75 ° and 13 8 ¯ 5 ¯ 3 90 ° , which showed the cusps in grain boundary energy and can stabilize the recrystallized grain embryo. The substantial prior deformed substructures of the employed TA15 sheet, viz., low angle grain boundaries and dislocations, can facilitate the formation of subgrains and nucleation, which brought about a mixture of continuous and discontinuous recrystallization, regardless of dynamic or static. During the hot tension, the activation of dislocations would accelerate the annihilation and rearrangement of dislocations, thus, recrystallization can take place more frequently, which finally leads to an equiaxed microstructure. • Quasi-in-situ annealing treatment of the initial TA15 sheet was carried out. • A mixture of continuous and discontinuous recrystallization was observed during annealing and hot tension. • Effect of substantial prior deformed substructure on the recrystallization behavior was investigated. [ABSTRACT FROM AUTHOR]

High-efficiency and low-cost hot forming technologies for titanium alloys have been developed for producing complex-shaped, thin-walled tubular components under non-superplastic forming conditions. Under these forming conditions, there exist complex and highly integrated material evolution processes including microscopic heterogeneous deformation, microstructure evolution and damage behaviour. This paper presents an integrated crystal plasticity finite element model of near-α titanium alloys during non-superplastic hot deformation conditions considering grain boundary sliding (GBS), dynamic recrystallisation (DRX), as well as void evolution. The polycrystalline model of a near-α TA15 titanium alloy was established, containing α phase, β phase and grain boundary (GB) regions, in which the GB region was a visualised representation of GBS. The quantitative strength ratio between the GB regions and α phase was calculated according to the Zener–Holloman parameter Z and grain size, which determined the microscopic deformation behaviour. There were found to be two high microscopic strain regions in the α phase: intragranular deformation bands through the most favourable slipping and near the GBs through multiple slipping, which promoted continuous and discontinuous DRX, respectively. With the decrease in parameter Z or grain size, the activated dislocations accommodating GBS were found to no longer pile up inside the grain, but instead travel across the grain interior. Finally, methods to improve the macroscopic plastic formability were proposed for the difficult-to-form titanium alloys experiencing non-superplastic hot deformation. [ABSTRACT FROM AUTHOR]

This study investigated the features of grain boundary regions in a Ni-based superalloy which underwent creep deformation. Large grain boundary zones were denuded in fine γʹ precipitates but contained coarsened microscale γʹ rods. The coarsening direction of these rods was along the <110> of the γ matrix and γʹ precipitates. The orientation of the grain boundary zone was the same as that of the adjacent grain behind the migrating boundary. This result indicated that the formation of these zones was accompanied by the migration of the grain boundary. Then, numerous slip features were observed through detailed local disorientation analysis. It is proposed that the driving force for the grain boundary migration was the local stress induced by the dislocation creep. The dissolution–reprecipitation of the precipitates at the boundary migration front resulted in the directional coarsening of the γʹ rods. [ABSTRACT FROM AUTHOR]