Microstructure evolution of Inconel 738 fabricated by pulsed laser powder bed fusion

High-density crack-free Inconel 738 samples were manufactured into both thin-walled and bulk samples using pulsed laser powder bed fusion (P-LPBF). As-built thin-walled samples presented a dendritic microstructure with primary dendrite arm spacing (PDAS) of 1.02 ± 0.21 µm. This PDAS was consistent along the length of the as-built wall, which led to a homogeneously distributed hardness across the deposit. Energy dispersive spectroscopy (EDS) maps showed near-equilibrium elemental segregation due to limited solute trapping occurring during rapid solidification. In the bulk of the as-built samples, a PDAS of 0.69 ± 0.06 µm was obtained. The smaller dendrite arm spacing which developed in the bulk was a result of the higher cooling rates obtained in this volume of sample. The EDS maps of the bulk samples presented comparative elemental constituents of the different phases as seen in the thin-walled sample. The Electron Backscattered Diffraction (EBSD) map of the bulk sample presented columnar grains with strong texture along the (100) crystallographic orientation planes. After annealing and aging treatment, cuboidal primary γʹ precipitates and secondary γʹ precipitates were observed. No strain–age cracks were found after the heat treatment. The EBSD map displayed comparative results to the as-built condition; with columnar grains with preferred orientation towards (100) planes.