Investigations of γ′, γ″ and δ precipitates in heat-treated Inconel 718 alloy fabricated by selective laser melting
Highlights: • The γ austenite matrix shows a fine cellular substructure. • γ′ and three variants of γ″ precipitates around 10–50 nm develop within cellular γ. • Coarser acicular γ″ and plate-like δ occur at grain boundaries and intragranular γ. • The orientation relationships of γ″ with γ, and of δ with γ are observed. - Abstract: Inconel 718 alloy samples were fabricated by selective laser melting (SLM). Microstructure and precipitation in solution-heat-treated- and double-aging-SLM-made Inconel 718 were studied by scanning and transmission electron microscopy. Electron microscope observations showed that disc-shaped and cuboidal γ″, and circular γ′ precipitates with an average size of 10–50 nm developed within cellular γ austenite matrix. The simulated, experimentally observed electron diffraction patterns, and dark-field imaging further revealed that the precipitation of three variants of γ″ in the γ matrix occurred. The coarser acicular γ″, and globular as well as plate-like δ phases precipitated at grain boundaries and also within the interior of austenite matrix. The morphology, distribution and crystallography of these precipitates and their formation mechanisms were analyzed and discussed.