A dislocation density-based model and processing maps of Ti-55511 alloy with bimodal microstructures during hot compression in α plus β region

Hot compression features of Ti-55511 alloy are investigated by high-temperature compression tests in alpha+beta 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 a phase and dynamic recrystallization (DRX) of beta phase easily occur at low temperatures such as 973, 1003 and 1033 K, while the dynamic recovery (DRV) of beta phase mainly occurs at high temperatures such as 1063 K because of the transformation from alpha phase to beta phase at relatively high temperatures A dislocation density-based constitutive model, which is associated with DRV, work hardening mechanisms and the spheroidization of alpha 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.