The optimal determination of forging process parameters for Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy with thick lamellar microstructure in two phase field based on P-map

The deformation behavior of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy with thick lamellar α microstructure is investigated by using the Processing-map (P-map). The results show that the P-map can predict the regime of flow instability and reveal deformation mechanisms well. Through analyzing P-maps and observing the microstructure evolution of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy in forging process, the phenomena of flow instability are found to occur at the temperature and strain rate ranges of (750-880 °C, 0.005-10.0 s-1) and (880-950 °C, 0.17-10.0 s-1), which include macrocracks, adiabatic shear bands and prior β boundary cavities. The preferable temperature and strain rate for hot working of the Ti-alloy are (790-900 °C, 0.001-0.003 s-1) and (900-950 °C, 0.001-0.017 s-1). In these two deformation domains, the globularization of α lamellae occurs, and the combination of the globularization of α lamellae and α + β → β phase transformation happen, respectively. For forging of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy in α + β phase field, the optimum temperature can be selected from the temperature range of 850-950 °C and the optimum stain rate is 0.001 s-1based on the volume fraction of α phase for obtaining the needed properties of forgings in design of forging processes.