Influence behavior and mechanism of γ′- or γ′′-precipitated phase types on damage resistance of heterogeneous interface in nickel-based superalloys

Abstract

The microstructure adjustment of Ni-based superalloys focuses heavily on the types of precipitated phases because the failures of Ni-based superalloys often occur at γ-matrix/γ′- or γ′′-precipitated phase heterogeneous interfaces. As different types of precipitate phases result in different interface damage resistances, the influences of the types of precipitated phases on the damage resistances of heterogeneous interfaces were investigated in this work. Based on the results of this work, the interfacial works of adhesion for the three interfaces composed of the γ-matrix and typical precipitated phases (γ′-Ni3Al, γ′-Ni3Ti, and γ′′-Ni3Nb) are 4.81, 3.88, and 4.26 J/m2, respectively, indicating that the γ-Ni/γ′-Ni3Al interface shows the highest cleavage fracture resistance. This can be attributed to the highest interfacial average charge density among all three interfaces. During interface tensile processing, all fractures occur in the precipitated phase, indicating that the ductility of heterogeneous interfaces is determined by that of the precipitated phase. Due to the highest ductility of γ′-Ni3Ti, the γ-Ni/γ′-Ni3Ti interface demonstrates the best plastic fracture resistance with the smallest Rice ratio of 4.89 and the largest maximum strain of 10 %, followed by the γ-Ni/γ-Ni3Al and γ-Ni/γ′′-Ni3Nb interfaces. The γ-Ni/γ′-Ni3Ti interface also exhibits the highest fatigue fracture resistance attributed to its strongest ability in hindering dislocation slipping with the lowest unstable stacking fault energy, followed by the γ-Ni/γ′′-Ni3Nb and γ-Ni/γ′-Ni3Al interfaces. These results conclude that Ni-based superalloys with γ′-Ni3Al as the main precipitated phase demonstrate high strength, while those with γ′-Ni3Ti as the main precipitated phase demonstrate high plastic and fatigue fracture resistances.