Nanometer-Scale Precipitations In A Selective Electron Beam Melted Nickel-Based Superalloy

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. gamma' 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. gamma' precipitates, similar to 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. gamma' 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. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.