Morphology-dependent creep and chemo-mechanical degradation in non-equilibrium CoNi-based superalloys

The creep resistance of γ'-strengthened CoNi-based superalloys is governed by the interactions of mechanical fields and localized chemical compositions, while the coupled chemo-mechanical origin and kinetics evolution under the creep stress at high temperature are still unclear. A phase-field crystal-plasticity model is proposed to investigate the morphology-dependent creep of the L1₂-γ'-(Co, Ni)₃Al phase in a newly designed CoNi-based superalloy. The non-equilibrium precipitate is incorporated to capture the microstructural asymmetry. Under 750 MPa stress, the Y-axis loading exhibits an extended creep life 5.3 times that of the X-axis loading, while the X-axis loading accelerates creep rafting instability. The X-axis stress exacerbates the local concentration of equivalent stress at γ matrix channels more than that of the Y-axis; the stress gradient triggers a chemo-mechanical coupling effect, driving the uphill diffusion and resulting in Al depletion and reduced γ' volume fraction. The localized γ' phase dissolution induces the equivalent plastic strain peaks, surpassing the critical threshold for topological inversion and structural degradation. This work quantitatively links localized chemo-mechanical degradation to macroscopic morphology-dependent creep failure, providing critical insights for the microstructural design of next-generation superalloys.