From melt pool to performance: A review of microstructural engineering in the additive manufacturing of nickel-based superalloys

Abstract

This review critically and systematically analyses recent progress in additively manufactured (AM) Ni-based superalloys, mapping processing–microstructure–property linkages relevant to qualification of hot-section hardware in aerospace and energy, including turbine blades, combustion chambers, and injectors. Comparisons are drawn across laser/electron powder-bed fusion and directed energy deposition. We explain how melt-pool dynamics and cooling rate govern grain architecture and boundary character, micro-/macro-texture, micro-segregation, and phase evolution-strengthening γ′/γ″ (γ'/γ'') and carbides versus deleterious Laves/TCP. Key defects, such as porosity, lack of fusion, hot cracking, and residual stress, are linked to the tensile response, hardness stability, and creep/fatigue resistance. Practical process windows are identified, and optimization strategies are synthesized in terms of power, scan speed, hatch spacing, layer thickness, preheating, shielding, and feedstock quality; for illustration, scan speeds on the order of 1100–1700 mm/s in l-PBF IN718 shift strength/porosity trade-offs. Post-processing routes (stress-relief, solution/aging, HIP) that reduce defects, tailor metastable constituents, and restore near-isotropy are summarized. Representative alloys (IN718, IN625, Hastelloy X) illustrate trade-offs between γ′ fraction, Nb-rich Laves formation, and build rate. Remaining gaps include standardized powder specifications, robust in-situ monitoring with model-informed control, cross-platform comparability, and long-duration oxidation/hot-corrosion datasets to support design allowable. Overall, the review offers practical guidance for engineering microstructure and properties in AM Ni-based superalloys and accelerates industrial qualification for critical service environments.