Defect-mediated topologically-close packed phase coarsening in Ni-based superalloys: atomic-scale insights

Understanding the mechanisms controlling topologically close-packed (TCP) phase nucleation and growth remains crucial yet unclear for designing advanced Ni-based superalloys, which are widely needed for low-CO₂-emitting advanced gas turbines. This study delivers the first combined atomic-scale and thermodynamic investigation of σ phase evolution, establishing a novel “interfacial defect-composition-structure” matching model for the morphological evolution of TCP phase. Atomic-resolution observation revealed unprecedented atomic misarrangement appeared at the interface between the habitant planes of σ and γʹ phase near the interfacial ledges, creating coherent transition zones that accelerated σ phase coarsening. These nanoscale structural anomalies provided both compositional and structural similarity between the σ phase and γʹ phase, thereby facilitating the coarsening of the σ phase. Theoretical calculations further confirm the thermodynamic stability for such interfacial configuration formation, thus thermodynamically favoring coarsening kinetics. Crucially, stacking fault energy (SFE) of the γʹ phase is established as the governing parameter controlling coarsening kinetics. External stress further accelerates coarsening by promoting similar defect formation. These findings proposed composition-based SFE control as a strategic pathway to design degradation-resistant superalloys.