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The precipitation orientation of α phases in a Ti-55511 alloy during the heat treatment and the subsequent hot deformation is investigated. It is observed that the β grains prominently influence the precipitation process of α phases, i.e., for the neighbouring β grains without similar {110} pole, the precipitation orientation of grain boundary (GB) α phases (α GB) keep {0001}//{110}β1 or {0001}//{110}β2 to maintain the burgers orientation relationship (BOR) with the neighbouring β grains. For the neighbouring β grains with similar {110} pole, the {0001} poles of α GB phases precipitate parallel to this similar {110} pole and maintain BOR with the neighbouring β grains. For the neighbouring β grains with multiple similar {110} poles, the {0001} poles of α GB phases precipitate along these similar poles and maintain BOR with the neighbouring β grains. Besides, the interface instability nucleation and sympathetic nucleation are the main nucleation modes of the GB widmanstatten α phase (α WGB), which primarily precipitate within β grains with the similar orientation of α GB phases. The intracrystalline widmanstatten phase (α WI) precipitate in a single β grain with 12 precipitation orientations. The BOR between α WI phases and β grains is destroyed during the subsequent hot compressive deformation. • Precipitation orientation of α phases in Ti-55511 alloy during heat treatment plus hot deformation is studied. • Precipitation orientation of GB α phases maintains the BOR with neighbouring β grains along different poles. • Interface instability and sympathetic nucleations are the main nucleation modes of GB widmanstatten α phases. • The intracrystalline widmanstatten phases (α WI) precipitate in a single β grain with 12 precipitation orientations. • The BOR between α WI phases and β grains is destroyed during the subsequent hot compressive deformation. [ABSTRACT FROM AUTHOR]

Hot compression features of Ti-55511 alloy are investigated by high-temperature compression tests in α+β region. It is found that the flow stress and softening mechanisms are obviously influenced by deformation conditions. The true stress decreases with the reduced strain rate or the raised temperature. The spheroidization of α phase and dynamic recrystallization (DRX) of β phase easily occur at low temperatures such as 973, 1003 and 1033 K, while the dynamic recovery (DRV) of β phase mainly occurs at high temperatures such as 1063 K because of the transformation from α phase to β phase at relatively high temperatures A dislocation density-based constitutive model, which is associated with DRV, work hardening mechanisms and the spheroidization of α phases, is established and validated to describe flow behavior. The correlation coefficient (R) and average absolute relative error (AARE) of the established model are 0.9924 and 6.8%, respectively. 3D power dissipation efficiency maps and processing maps are established to determine the appropriate processing window, i.e., too low temperatures (lower than 973 K) or too high strain rates (higher than 1 s−1) easily induce flow instability. Therefore, the medium temperature (1003–1063 K) and the low strain rate (0.001–0.1 s−1) are applicable for thermal compression of the studied titanium alloy. • Hot compression features of Ti-55511 alloy is investigated by high-temperature compression tests in α+β region. • DRX easily occurs at low temperatures, while DRV mainly occurs at high temperatures. • A accurate dislocation density-based constitutive model considering the spheroidization of α phases is established. • The optimal forming temperature and strain rate are 1003–1063 K and 0.001–0.1 s−1. [ABSTRACT FROM AUTHOR]

Spheroidization and dynamic recrystallization (DRX) mechanisms of a Ti-55511 alloy during hot compression in α+β region is investigated. It is found that the spheroidization of lamellar α phases and DRX of β phases, which are obviously influenced by deformation conditions, are the main softening mechanisms. The spheroidization fraction of lamellar α phases first increases with the raised temperature or strain rate. However, the spheroidization fraction of lamellar α phases begins to drop at about 700 °C as the strain rate is higher than 0.01 s−1, and the maximum spheroidization fraction of lamellar α phase is about 2.3%. This phenomenon is attributed to the Implanting-Mechanism, which is induced by the common or close orientation relationships of the spheroidized and equiaxed α phases, as well as few dislocations between the spheroidized and equiaxed α phases. Contrarily, the lamellar α phases are obstructed from equiaxed α phases by a mass of dislocations. Additionally, the DRX degree of β phases increases with the reduced temperature or the raised strain rate. • Spheroidization and DRX mechanisms of a Ti-55511 alloy during hot compression in α+β region is investigated. • Spheroidization fraction of lamellar α phase first increases then drops with the raised strain rate. • The maximum spheroidization fraction of lamellar α phase is about 2.3% near 700 °C and 0.01 s−1. • Implanting-Mechanism, induced by the close orientation relationships of spheroidized and equiaxed α phases, is proposed. • The DRX extent of β phases increases with the reduced temperature and raised strain rate. [ABSTRACT FROM AUTHOR]