Influence of long-term isothermal aging on microstructure and creep rupture properties of Ni-base superalloy M4706

After a standard heat treatment, the microstructural evolution with time during isothermal aging at 850 °C and its effect on the creep rupture properties of the Ni-base superalloy M4706 at 870 °C and 370 MPa are investigated. It is found that as the aging time increases from 0 to 5000 h, the average diameter of coarse γ’ increases from 241 to 484 nm, and the distribution of the carbides at grain boundaries changes from discontinuous to continuous. Moreover, experimental observations on the microstructures of all the crept specimens reveal that dislocation bypassing controls the creep deformation. Thus, it is concluded that the transitions in the microstructures result in the degeneration of the creep rupture properties of the experimental alloy with aging time.