The kinetics of static globularization of Ti-6Al-4V

The kinetics of the evolution of the lamellar-colony microstructure to an equiaxed morphology during heat treatment of a hot-worked, two-phase titanium alloy were established. For this purpose, the alpha/beta alloy Ti-6Al-4V was isothermally upset forged at 900 °C or 955 °C and subsequently annealed for times ranging from 0.5 to 100 hours. The degree of the breakup of alpha-phase lamellae into lower-aspect-ratio grains during static annealing was measured and related to the imposed strain estimated using finite-element analysis (FEA). The kinetics of the static globularization of the alpha phase were found to depend on the amount of strain and the annealing temperature but were not affected by the specific deformation temperature in the 900 °C to 955 °C range. These results demonstrated that deformation-induced dislocation substructure has a small effect on the static-globularization process. In addition, the relative globularization kinetics at 900 °C and 955 °C were rationalized in terms of classical coarsening theory.