Effect of original microstructure on the hot compression behavior of superalloy 718

Hot compression tests at different temperatures and strain rates were performed on superalloy 718 annealed at 1100 °C for 30 min as well as 950 °C for 30 min in order to investigate the effect of the original microstructure on the hot deformation behavior. The results show that the δ phase precipitated on the grain boundaries of superalloy 718 prior to hot deformation leads to a decrease of the flow stress, which can be attributed to the drop of the matrix strength. The activation energy (Q) for hot deformation of the fine-grained material with δ phase on the grain boundaries is determined to be 381 kJ/mol, which is much lower than that of the coarse-grained material without δ phase (472 kJ/mol). It is suggested that the initial S phase precipitated on the grain boundaries of the annealed material affect the thermal activation process of hot deformation for superalloy 718, resulting in the decrease of activation energy.