Atomic mechanism of the Re and Ru strengthening effect on the γ-γ′ interface of Ni-based single-crystal superalloys: A first-principles study

A possible atomic mechanism underlying the Re- and Ru-induced strengthening effects on the n- n' interface in Ni-based single-crystal superalloys has been investigated using the DMol3 molecular orbital package based on density functional theory. The calculation of bonding properties has been performed on a cluster designed to model Re and Ru strengthening effects within the interface. The stronger Re(Ru)--Ni bonds are formed mainly as a result of (Re(Ru) d-(Ni d) hybridization, while the Ni--Ni bonding become weaker accompanying the Re(Ru) substitution. The vertical and horizontal bond orders for a local environmental cluster are proposed and developed for the description of the strengthening effect on the n- n' interface, with larger bond order values achieving better effect. Results show that both Re and Ru significantly strengthen the interface. It is also shown that the strengthening effect of Re is better than that of Ru, and this is explained in terms of the charge transfer of electrons between orbitals of Ru atom according to Mulliken population analysis. The calculation results provide a basis for understanding the atomic mechanism of Re- and Ru-induced n- n' interfacial strengthening.