Effect of the δ phase on the hot deformation behavior of Inconel 718

Hot compression tests at different temperatures and strain rates were performed on Inconel 718 solution treated as well as solution treated and then aged at 900 °C for 1–24 h in order to investigate the effect of the δ phase on hot deformation behavior. A hyperbolic-sine Arrhenius-type equation was used to characterize the dependence of the peak stress on deformation temperature and strain rate. In the case of Inconel 718 with a large amount of the δ phase, the apparent activation energy was determined to be 458 kJ/mol, which was slightly higher than the activation energy of 443 kJ/mol for solution treated Inconel 718. The γ″/γ′ phases present in Inconel 718 prior to hot deformation enhanced the peak stress, but did not affect the peak strain. The δ phase present in Inconel 718 not only decreased the peak strain and the peak stress, but also promoted the flow softening after the peak stress.