The strengthening effect of Ta-W/Mo mediated by their partitioning behaviors in Ni-based single-crystal superalloys: Insights from first-principles calculations

Ni-based single-crystal (SX) superalloys exhibit complex chemical interactions among various alloying elements, affecting their partitioning behavior between γ-Ni and γ'-Ni₃Al phases. This makes the mechanical properties of superalloys strongly dependent on alloy composition due to the impacts of elemental partitioning on the interfacial strength. In this work, the site occupation and partitioning behavior of Ta-X (X = Mo, W) in γ-γ' dual-phase have been studied by using a novel first-principles method proposed for calculating elemental concentration in co-alloyed dual-phase systems at finite temperature. Our results demonstrate that increasing Ta content suppresses the original substitution tendencies of W and Mo in γ' phase and leads to their preferential partitioning to γ phase consequently. In both γ and γ′ phases, the chemical effect from Ta–W/Mo substitution consistently stabilizes the system while local lattice distortion effect destabilizes the system. Focusing on the γ/γ' interface, W and Mo are verified to segregate on the γ-side layers regardless of Ta's location. Furthermore, the Ta-W/Mo co-alloying is proved to enhance the Griffith work of γ/γ' interface with Ta doped on γ' side. The even stronger strengthening effect of γ'-side Ta-W/Mo co-alloying is attributed to the substitutions of weaker Al-Ni bonds by stronger Ta-Ni, W-Ni and Mo-Ni bonds. This work is expected to provide a theoretical guideline to strengthen the Ni-based SX superalloys via the regulation of W/Mo partitioning by Ta content.