Temperature-dependent γ′ kinetic evolution and elemental partitioning in a novel CoNi-based superalloy: an integrated CALPHAD, phase-field, and experimental study

Abstract

Co–Ni-based γ/γ′ superalloys are promising candidates for next-generation turbine blades, yet achieving high γ′ stability and low density remains a significant challenge. This study presents a physics-constrained, integrated CALPHAD-phase-field methodology to design a novel Co–36Ni–15Al–3Ti  (at%) alloy with an ultra-low density of 8.06 g cm⁻³. By implementing a screening framework governed by seven distinct thermodynamic and kinetic criteria, we successfully eliminated deleterious TCP phases while maintaining a high γ′ volume fraction of 70%. A transformative concept, temperature-activated microstructural adaptability, is introduced, where elevated temperatures from 1074 to 1124 K trigger a reversible redistribution of Ti and Al atoms between the γ and γ′ phases. Phase-field simulations validated by experimental characterization reveal that this element redistribution dynamically optimizes the lattice mismatch from 0.803% to 0.725%, effectively balancing the internal elastic strain and interfacial energy. Consequently, the alloy exhibits an exceptional yield strength of 1275 MPa at a high temperature, surpassing conventional Co–Al–W-based superalloys and showing superior strength than the commercial Ni-based single crystals. This work provides a generalized paradigm for designing adaptive, high-performance structural materials through the synergy of multi-component thermodynamic and kinetic evolution.