Effect of Heat Treatment on the Microstructure and Fracture Behaviors of a Ni–Cr–Fe Superalloy

The influences of the size and shape of the γ′ phase and the type and distribution of carbides on the fracture behavior of a new Ni–Cr–Fe superalloy subjected to four different solution aging treatments are examined. The γ′ phase and γ matrix of the L1₂‐ordered structure maintain a coherent orientation relationship on the {100} and {110} atomic planes according to transmission electron microscopy observations. The material becomes stronger because the movement of dislocations is hindered by the γ′ phase and MC (Nb‐rich, Ti‐rich) and M₂₃C₆ (Cr‐rich, Mo‐rich) carbides. The two‐stage aging system (850 °C × 4 h + 730 °C × 4 h) substantially increases the size of the γ′ phase. The solid solution sample shows a microporous‐aggregated ductile fracture, and the solution‐aged samples show a microporous‐aggregated crystalline fracture according to scanning electron microscopy observations. The fracture mechanism is also discussed.