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−1 based on the volume fraction of α phase for obtaining the needed properties of forgings in design of forging processes.