Morphological and Textural Evolution of the Alpha Phase during Hot Deformation of Two-Phase Ti-6Al-4V

The deformation behaviour and associated microstructural evolution during hot forging of Ti-6Al-4V with a range of initial alpha lamellar microstructures has been examined. Uniaxial compression tests were carried out at temperatures both low and high in the alpha+beta stability field, 880 degrees C and 950 degrees C respectively, using strain rates (0. 01,0. 1 and 1/s) relevant to industrial press forging. Orientation image mapping and texture analysis of the alpha phase was used to examine the progressive break-up of the initial structure during the early stages of spherodisation (epsilon <= 1). Results indicate that, for the microstructures examined, there is no influence of alpha lath thickness on overall stress-strain response. Flow softening and the attainment of a steady state flow stress appears to be associated with progressive realignment of alpha laths with their long axes perpendicular to the compressive loading direction, rather than with spherodisation of the alpha structure. At 950 degrees C the development of a single-pole basal texture indicates that the alpha laths become oriented predominantly in a single transverse orientation. At 880 degrees C deformation also leads to a transverse basal texture, but with the laths distributed radially about the axi-symmetric loading direction.