Mechanical and microstructural properties of IN718 additively manufactured lattice structures

In this work, a mechanical and microstructural characterization of IN718 lattice structures prepared by additive manufacturing has been carried out. The goal is to investigate the link between macroscopic behaviour and microscopic properties, comparing bulk sample with lattice structures. From a mechanical point of view, all the investigated lattice structures can be classified as bending dominated. They show Ashby's coefficients CE of 3.20, 2.61 and 2.53 and Cσy of 0.42, 0.38 and 0.34, for diamond, body diagonals with rounded nodes and rhombic dodecahedron cell structures, respectively. From the microstructural analysis, crossed elongated melt-pools and mostly equiaxed grains have been observed, along the plane perpendicular to the building direction, while arc-shaped melt-pools and elongated grains have been detected on the plane parallel to the building direction. All samples were found to be slightly textured along the (100) direction. The degree of preferred orientations η, calculated from the March-Dollase coefficients extracted from the Rietveld refinement of XRD patterns, is similar for both bulk sample and lattice structures, being approximately equal to 26 % for both xy and xz sides. Calorimetric analysis detected the precipitation of secondary phases at specific temperature ranges. The presence of secondary phases has been also confirmed by the SEM micrographs showing similar precipitates. Overall, no significant difference was found between bulk samples and lattice structures in terms of grain size, grain shape, phase composition, texture, and other metallurgical properties.