Thermal Stability of γ/γ' Coherent Microstructure and Mechanical Properties of High-strength Ni-Co-based Wrought Superalloy

A novel Ni-Co-based wrought superalloy with the nominal composition Ni-Co-2.66Al-3.3Ti-1.37Nb-2.66Ta- 12.29Cr-2.83Mo-5.41W-0.08C-0.02B-0.03Zr(wt%) was designed by employing the cluster formula approach combined with the high-entropy alloying principle. The alloy ingot was prepared by vacuum non-consumablevacuum arc melting, followed by solid-solution treatment at 1100 C for 1 h and subsequent aging treatment at 850 ℃ for 1000 h. The microstructural characterizations and mechanical property tests of the aged specimens were carried out. The results reveal a typical coherent γ/γ' microstructure characterized by a high volume fraction (about 54%) of cuboidal γ' nanoparticles that uniformly precipitated within the FCC-γ matrix. After prolonged aging for 1000 h, the γ' precipitates exhibit an extremely low coarsening rate(K=0.26 nm³/s), and the microhardness remains nearly unchanged (412 HV-458 HV), which demonstrates the exceptional thermal stability of the γ/γ' coherent microstructure. The alloy aged for 50 h achieves a yield strength of 1090 MPa at room temperature and retains a high yield strength of 900 MPa at 800 ℃, indicating outstanding mechanical performance. Quantitative analysis of the strengthening mechanisms shows that precipitation strengthening is the dominant contributor, accounting for approximately 724 MPa.