An Investigation of the Development of Coarse Grains During β Annealing of Hot-Forged Ti-6Al-4V

Process variables contributing to the development of non-uniform, coarse grains during β annealing following subtransus conventional forging of the α/β titanium alloy Ti-6Al-4V were investigated using subscale laboratory experiments and simulations of the evolution of the β-phase crystallographic texture. Forging trials comprised the nominally plane-strain sidepressing of cylindrical preforms using a furnace (preheat) temperature of either 1172 K, 1186 K, or 1227 K (899 °C, 913 °C, or 954 °C) and diametral reductions between 40 and 70 pct. Following hot working, cross sections of each workpiece were β annealed for 1 h at 1311 K (1038 °C). Bands of β grains whose size were at least twice that in the surrounding matrix were found to be prevalent in regions whose deformation was close to plane strain for forging experiments involving the highest level of reduction and the highest preheat temperature. Electron backscatter diffraction (EBSD) analysis of the forged-and-heat-treated samples indicated that such regions had developed a strong rotated-cube β microtexture during forging (and the early stages of annealing). This promoted the enhanced growth of a small volume fraction of highly-misoriented grains. These observations were interpreted in the context of coupled (continuum) finite-element method simulations of metal flow during forging and viscoplastic, self-consistent calculations of the concomitant evolution of deformation texture to elucidate the interdependence of forging temperature, phase fractions, strain partitioning between the two phases, and texture evolution.