Local composition and nanoindentation response of δ-phase and adjacent γ′′-free zone in a Ni-based superalloy

Abstract

Experimental differentiation of individual strengthening effects from the nanoscale precipitates in Alloy 718 remains challenging due to co-precipitation of γ′ and γ′′. Here, we examine a region adjacent to the δ-phase consisting of γ-matrix containing γ′-precipitates only. The width and compositional profile of this γ′′-free zone is uncovered via high-resolution characterization. Nanomechanical analyses reveal that the lack of γ′′-precipitates lower the hardness of the γ′′-free zone by 10–20%, while the δ-phase is found to be ∼80% harder than the γ-matrix. These findings may guide mechanical modelling and microstructural engineering of stronger superalloys critical to aerospace industry.