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

Abstract

The influences of the size and shape of the γ 0 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 0 phase and γ matrix of the L1 2-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 0 phase and MC (Nb-rich, Ti-rich) and M 23 C 6 (Cr-rich, Mo-rich) carbides. The two-stage aging system (850 C Â 4 h þ 730 C Â 4 h) substantially increases the size of the γ 0 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.