Microstructures and homogenization behavior of a nickel-based superalloy used for 850 ℃ turbine disc prepared by electron beam smelting layered solidification

Abstract

Electron beam smelting layered solidification technology is applied to prepare a nickel-based superalloy for turbine disks with service temperature up to 850 ℃. The microstructures, segregation and homogenization behavior were investigated. The results show that there is a cellular crystal structure with a width of 1.5 mm between the layers, and the dendritic structure is observed within the layers. The average secondary dendrite arming spacing is 28.6 µm, which attributed to higher temperature of molten pool and faster cooling rate. After electron beam smelting layered solidification technology, the macrosegregation is eliminated, and the microsegregation is weakened. The average temperature on the molten pool surface during electron beam smelting is 1813 K according to evaporation rates of Ni. The effect of homogenization treatment on the microstructures and microsegregation evolution was discussed. Based two diffusion models, the diffusion coefficient of Nb and W at 1190 °C are calculated as 7.365 × 10−16 m2/s and 5.805 × 10−16 m2/s, respectively.