Additive manufacturing of nickel-based superalloy Inconel 718 by selective electron beam melting: Processing window and microstructure

Cube-shaped IN718 samples were produced by selective electron beam melting (SEBM) with varying beam power, deflection speed, and beam spot size. Process parameter windows were identified where fully dense samples are obtained with no surface unevenness. High deflection speeds were demonstrated to result in smaller demand of area energy. This result is explained by the reduced time for heat dissipation into the substrate during hatching. The grain structure was strongly affected by SEBM process parameters. Under certain conditions, epitaxial growth over many layers and well-developed columnar grain structures were obtained with a polycrystalline substrate plate. A more defocused beam led to a lower melt pool temperature and shallower melt pool geometry where maximum temperature gradients and solidification rates were more or less in parallel with the building direction and primary dendrite arm orientation. These conditions help to suppress grain nucleation ahead of the nucleation front as vigorous melt movement, fragmentation of dendrites, and tertiary arm growth are suppressed.