Influence of post-processing on the microstructure and mechanical properties of high-strength Ni-Co-base wrought superalloy

In this study, the influence of post-processing on the microstructure and mechanical property of the novel Ni-Cobase wrought high-strength superalloy with a composition of Ni-(24.0-26.0)Co-(2.3-2.7)Al-(2.8-3.3)Ti-(1.3-1.8) Nb-(12.0-14.0)Cr-(2.6-3.0)Mo-(1.0-1.5)W-(0.01-0.03)B-(0.01-0.05)C-(0.01-0.05)Zr (wt.%) was investigated. Two post-processing routes were carried out on the superalloy, in which one is solid-solution and double-aging (S1-SA), and the other adds a cold-rolling between them (S2-SRA). It is found that both the FCC-gamma matrix grains and the precipitated trimodal gamma ' particles are not sensitive to the post-processing, showing a comparable distribution in these two states. However, a large amount of dislocations, stacking faults, Lomer-Cottrell locks, and deformation twins induced by the cold-rolling, were not eliminated by subsequent double-aging in S2-SRA. The superalloy exhibits high yield strength at both room and elevated temperatures in both states, as exampled by 1126 MPa at RT and 912 MPa at 1023 K in S1-SA and 1855 MPa at RT and 1086 MPa at 1023 K in S2-SRA, respectively. The high strength was further discussed with various strengthening mechanisms, in which the precipitation strengthening is dominant. And the much higher strength in S2-SRA is attributed to the contributions from both high-density dislocations and deformation twins.