Ti-6Al-4V on-cooling flow stress behaviors study with Gleeble 3500

During the forging process in industry application, the creep during cooling (after forging) was hard to predict as the flow stress data were usually collected at constant temperatures. In this study, a less traditional thermal-mechanical physical simulation approach that investigates the on-cooling flow stress behaviors were performed by Gleeble 3500. The Gleeble samples were machined from a Ti-6Al-4V billet to several 10 mm diameter cylinders. The samples were heated to either 1775F or 1925F (below or above beta transit), soaking for several seconds, followed by cooling to 1000F. During cooling, 0% to 6% of total transverse strain was applied with the different cooling rates (25F/min to 1000F/min), combined with the thermal contraction, some thermal-mechanical properties presented. The samples were subjected to XRD measurement after the Gleeble test using the Sin²ψ method to get the surface residual stress, sample was cut for metallography studies afterward. Temperature, stress, sample diameter, transverse strain, and stroke data as a function of time were collected during Gleeble tests. Two inflection points are shown on the stress-strain curves, indicating distinct strain hardening during cooling. While before the Gleeble tests the as-received samples all have compressive residual stress on the surface, all the samples show less compress stress or tensile stress afterward. The flow stress behaviors of Ti-6Al-4V during cooling as a function of strain, cooling rate, and temperature were discussed combined with the Gleeble data, XRD residual stress results, and the microstructure. The results provide inputs in modeling to predict the forging practice at better accuracy in industry applications.