Research on pore closure behavior and microstructure evolution during hot isostatic pressing of Ti6Al4V alloy casting

Hot isostatic pressing (HIP) has an important influence on the pore closure behavior and the microstructure evolution around pores in Ti6Al4V alloy castings. Therefore, experiments including the preparation of HIP samples and interrupted HIP experiments, and finite element numerical simulations were used to analyze the evolution of pore volume, distribution of stress and strain in Ti6Al4V alloy during HIP. After the mechanical closure of pores, molecular dynamics simulations were used to study the effect of temperatures and numbers of grains on the micropore closure. Finally, SEM/EBSD methods were applied to characterize the evolution of microstructure around the pore. The results show that creep is mainly contributed to the pore closure in the Ti6Al4V alloy during HIP, and the pore volume decreases by 96% after the step of raising temperature and pressure (first stage of HIP), the pore closure mainly occurs in the first stage of HIP. Grain boundary diffusion is the main mechanism for micropore closure. In addition, with the increase of HIP duration, the volume fraction of spheroidized α grains around pores is getting larger, the main mechanisms of spheroidization of α lamellae around the pore during HIP are continuous dynamic recrystallization and lamellae kinking.