Microstructure evolution of IN718 alloy during the delta process

Abstract

For the Delta Process of IN718 alloy, the microstructure evolution of IN718 alloy was studied by isothermal compression test at the temperature range 950~1010°C and strain rate range 0.005~0.1s-1 and heat treatment test at 950~1040°C after deformation. The result indicated that the main soft mechanism during hot working was dynamic recrystallization (DRX), and the phase boundaries between the δ phase and matrix were the nucleation sites for DRX. In addition, as a result of deformation breakage and dissolution breakage, the plate-like δ phase was spheroidized and transferred to spherical δ phase particles during hot working. During the holding period after deformation, the grain growth was restrained due to the pinning effect of δ phase, and the dissolution of δ phase occurred. As the heat treatment temperature was 950°C, the main microstructure evolution was the static recovery. However, as the heat treatment temperature increased to 980°C, the δ phase dissolved largely, and the main microstructure evolution was the grain growth and the formation of annealing twins. Therefore, the heating and deformation temperature should be in the range of 950 ~ 980°C for the Delta Process.