Deformation bands in a Ti17 alloy during deformation above the β-transus temperature

Deformation bands (DBs) can occur in Ti-alloys under specific deformation conditions and have a local nature that may lead to local damage. In this work, we developed a mean-field model based on the evolution of three types of dislocation densities to account for the development of DBs in the single β -field of Ti-alloys. The model considers the β -phase as a matrix in which DBs develop, bounded by highly rotated thin regions known as transition bands (TBs). While both the matrix and DBs deform through dislocation glide and climb with similar kinetics. The TBs, characterized by a significantly higher dislocation density, deform at a much higher strain rate. The model correlates the total flow stress with the microstructure using a rule of mixtures of the components and describes the microstructural evolution through the Kocks-Mecking formalism. The model was calibrated and validated with flow stresses and microstructure observations from hot compression tests on a Ti17 alloy at temperatures ranging from 930 °C to 970 °C and strain rates from 0.001 s -1 to 10 s -1 . The β -phase matrix and DBs were characterized using optical microscopy analysis and electron-backscattered diffraction (EBSD). Both experimental and modeling results assign the stress softening of Ti17 due to the formation of TBs and DBs. These bands preferably initiate within prior- β grains with high Taylor factors under high stresses and then accommodate the plastic strain by forming lower Taylor factor regions. As the plastic strain increases, the TBs become serrated, and dynamic recovery (DRV) followed by continuous dynamic recrystallization (CDRX) occurs in the interior of the DBs. At lower global strain rates and higher deformation temperatures, the formation of DBs is suppressed due to the fast interaction, annihilation, and reorganization of dislocations. • A mesoscale model for describing the formation of deformation bands in β-phase Ti alloys • Flow softening in β-phase Ti alloys induced by deformation bands • Microstructural heterogeneity accounting for both deformation bands and transition bands