The strengthening effects of Re-X (X[dbnd]Mo, W, Cr Ta, Re) mediated by their local partitioning behaviors at γ/γ′ interface in Ni-based single crystal superalloys

In Ni-based single crystal (SX) superalloys, the local partitioning behaviors of solute elements at γ/γ′ interface directly determine the structure and strength of the interface, which in turn have a significant effect on the mechanical properties of superalloys. As a characteristic strengthening element, Re has become indispensable in modern Ni-based SX superalloys in spite of its high cost. In order to unveil the strengthening mechanisms of Re combined with other alloying elements, the local partitioning behaviors of alloying atoms X (X[dbnd]Mo, W, Cr, Ta, Re) at the γ/γ′ interfaces with and without Re were investigated by first-principles calculations. An innovative quantity called layer concentration was defined and calculated to study the distributions of the alloying elements near γ/γ′ interface. The results show that Mo, W, Re and Cr are soluble in the nearest layer to the coherent plane on γ side most, while Ta is soluble in the nearest layer to the coherent plane on γ′ side most. An extra Re atom fixed at its most preferable site increases the partitioning tendencies of X to γ all, although it does not change the most preferable site of X. The presence of X also increases the layer concentration of Re in its favorable layer. Both single-alloying X and co-alloying Re-X could stabilize and strengthen the γ/γ′ interface with enhanced Griffith rupture works. Especially, for γ phase solid solution elements, Re-W co-alloying has the strongest strengthening effect on the interface, followed by Re-Re unexpectedly. Therefore, properly replacing Re with W could theoretically play an important role in improving the interfacial strength. The obtained results give an insight into the strengthening mechanism on atomic scale focusing at γ/γ′ interface area and pave a way to design high-performance low-cost Ni-based SX superalloys in future.