Influence of Post-Processing on the Microstructure and Mechanical Properties of High-Strength Ni-Co-Base Wrought Superalloy

Abstract

The present work investigated the influence of post-processing on the microstructure and mechanical property of a novel Ni-Co-base 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.%). 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 solid-solution and double-aging (S2-SRA). It is found that both the FCC-g matrix grains and the precipitated g' particles are not sensitive to the post-processing, where the grain size of the matrix, as well as the particle size and volume fraction of trimodal g' precipitates are comparable in these two states. However, the cold-rolling produced a large amount of dislocations, stacking faults, Lomer-Cottrell locks, and deformation twins, which were not eliminated by subsequent double-aging. The superalloy exhibits high yield strength at both room and elevated temperatures in both states, being 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 external strength increment between these two states is ascribed mainly to the contributions from both high-density dislocations and deformation twins in S2-SRA.

Keywords: Ni-Co-base wrought superalloy, post-processing, Microstructure, mechanical property, Strengthening Mechanism