Microstructure evolution of a new directionally solidified Ni-based superalloy after long-term aging at 950 °C upto 1 000 h

The microstructure evolution of a new directionally solidified (DS) Ni-based superalloy used for gas turbine blades after long-term aging at 950 °C was investigated. The results show that the γ' phase becomes more regular in dendritic arm and interdendritic area, while both the mass fraction and the size of γ' phase increase gradually with increasing aging time. During long-term aging, the MC carbide dissolves on the edge to provide the carbon for the formation of M23C6 carbide by the precipitation of Cr at the grain boundary. The rose-shaped γ'/γ eutectic partly dissolves into γ matrix and the aging promotes it transform into raft-shape γ'. The microstructure is generally stable and no needle-like topologically close-packed phase (TCP) can be found after aging for 1 000 h.