Microstructural characterization of hot deformed Ti-6A1-4V

The influence of the thermomechanical processing parameters on the microstructure is investigated in this work to define criteria to control and optimize of the forming processes. The mechanical properties of structural aircraft parts are strongly related to the microstructure obtained during forging and heat treatment processes, Pre-forged specimens of alpha-beta Ti-6A1-4V alloy with elongated primary α grains are deformed below and above the beta transus temperature between 0.001 and 10s^-1 of strain rate. The local strain within the samples is determined by finite element methods and correlated to the microstructure. Compression in α+β field is carried out parallel and perpendicular to the preferential orientations of the primary α grains. The α content is affected by the temperature of deformation and the morphology of the α grains is influenced by the strain and strain rate. Specimens with previous primary α grains parallel to the compression axis show a rotation of the α grains perpendicular to the load axis, EBSD measurements are used to determine the restoration mechanism involved during hot deformation. At large strains, continuous dynamic recrystallization by lattice rotation in the α grains is revealed by increasing the cumulative crystallographic misorientation towards the grain boundary and the formation of new grains. This effect increases with increasing values of the Zener Hollomon parameter (Z), For lower values of Z restoration occurs mainly in the beta phase. During deformation in β field, the β grains become elongated with the strain where dynamic recovery is the main mechanism activated. Static recrystallization after deformation is quantified, and a larger amount of grains when strain rate increases, is observed.