Unraveling the formation mechanism of hydrogenated vacancy at γ-Ni/γ'-Ni3Al phase interface and its roles in interfacial stability and strength

Abstract

γ/γ' phase interfaces are hidden troubles that threaten the service safety of Ni-based single crystal superalloys due to their thermodynamic instabilities and lower mechanical strengths. To gain insights into the role of hydrogenated vacancy in the stability and cohesion of γ/γ' interfaces, the formation mechanism of hydrogenated vacancy at (001) γ-Ni/γ'-Ni3Al interface and its influences on interfacial stability and fracture strength were systematically studied by using first-principles calculations. Our results show that the short-range interplay between monovacancy and single hydrogen atom at (001) γ-Ni/γ'-Ni3Al interface causes the formation of Vac-H complex structure (i.e., hydrogenated vacancy) as separated by a certain distance rather than a direct recombination. The hydrogen atom in the first nearest-neighbor interstices of Ni vacancy (site 6) deviates from the interstitial centers to the vacancy, owing to the interattraction between monovacancy and hydrogen atom. The formation of hydrogenated vacancy at (001) γ-Ni/γ'-Ni3Al interface can promote the interfacial thermodynamic stability as compared with the vacancy-containing γ/γ' interface, but weaken the interfacial fracture strength and change the preferable fracture place of γ/γ' interface. The underlying mechanisms of stabilizing and weakening effects on the γ/γ' interface were revealed by using spin-polarized density of states and differential charge densities.