Segregation of alloying elements and their effects on the thermodynamic stability and fracture strength of γ-Ni/γ′-Ni3Al interface

Abstract

The γ/γ’ phase interface, being the main plane defect in nickel-based single-crystal superalloys, can have a significant effect on the microstructural stability and mechanical properties of superalloys. To improve the thermodynamic stability and fracture strength of the γ-Ni/γ’-Ni3Al interface and gain insight into the underlying micro-mechanisms, the segregation tendency of 12 alloying elements X at the γ-Ni/γ’-Ni3Al interface and their effects on the interfacial formation and Griffith fracture works were investigated by using first-principles calculations. It is found that all alloying elements X can segregate to the corner-point site of the γ-Ni (001) layer except the element Y. The Re-, Ti-, Mo-, W-, Cr-, Nb-, Ta-, Hf- and Zr-segregated interfaces are more stable than the unalloyed interface due to the presence of pseudogap and lower values of densities of states at the Fermi level. The segregation of Ru, Co, Re, Mo, W, Cr, Nb and Ta strengthens the interfacial fracture strength, which can be mainly attributed to the enhanced bonding strengths of X–Ni bonds formed in these segregated interfaces. The interfacial segregation of Cr, Re, Mo, W, Nb and Ta can not only improve the thermodynamic stability but also enhance the fracture strength of the phase interface. The segregation of Ta and Re is able to improve the thermodynamic stability and fracture strength of the γ-Ni/γ’-Ni3Al interface to the maximum extent, respectively. The effect of interfacial segregation of alloying elements on the fracture strength and thermodynamic stability of the γ-Ni/γ’-Ni3Al phase interface and the underlying mechanisms are studied.