Nanometer-scale precipitations in a selective electron beam melted nickel-based superalloy

Abstract

The nanometer-scale (nano-scale) microstructural evolution in an additively manufactured Re-free Ni-based superalloy, with single crystal compositions, is investigated through field emission scanning electron microscopy, transmission electron microscopy, and atom probe tomography. We find that nano-scale primary γ′ precipitation occurs in the fine as-built microstructure, leading to an exceptional microhardness of 480.0 ± 6.7 HV at room temperature. Presence of ultra-fine γ′ precipitates, ~ 20 nm in size, is observed in the bottom few layers of the as-built samples, which is hitherto undocumented and contrary to the widespread consensus regarding hierarchical γ′ phase evolution in additively manufactured Ni-based superalloys. Moreover, considerable precipitation of tantalum-rich C14 Laves phase at the grain boundaries and interdendritic regions in the as-built samples emphasizes the need for additive manufacturing specific alloy design.