Microstructural evolution and compressive deformation of a new Ni-Fe base superalloy after long term thermal exposure at 700 °C

A new Ni-Fe base superalloy for applications of advanced ultra-supercritical (A-USC) boiler tubes was heat treated to three different statuses, i.e. aging treatment, aging treatment plus 1000 h and 7000 h thermal exposure at 700 °C. The specimens with various heat treatments have been compressed at 700 °C. The yield strength first increased with thermal exposure time and decreased after further thermal exposure. After aging treatment and 1000 h thermal exposure, deformation was heterogeneous, and dislocation slip combing climb was dominant process. However, after 7000 h thermal exposure, deformation became homogeneous. Stacking faults shearing the γ′ precipitates were also observed. The coarsening of γ′ precipitates and α-Cr precipitation occurred during long term thermal exposure. The influence of microstructural evolution on the yield strength and deformation mechanisms is discussed.