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

摘要

The deformation behavior of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy with thick lamellar a 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 ℃, 0.005-10.0s~(-1)) and (880-950℃, 0.17-10.0s~(-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 ℃, 0.001 -0.003 s~(-1)) and (900-950 ℃, 0.001-0.017 s~(-1)). In these two deformation domains, the globularization of α lamellae occurs, and the combination of the globularization of a 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 ℃ and the optimum stain rate is 0.001 s~(-1) based on the volume fraction of a phase for obtaining the needed properties of forgings in design of forging processes.