Effect of layer thickness, and laser energy density on the recrystallization behavior of additively manufactured Hastelloy X by laser powder bed fusion

A single-phase Ni-superalloy (Hastelloy X) was fabricated by laser powder bed fusion (L-PBF) using different layer-thicknesses (i.e., 40, 60, 80, and 120 µm), by implementing different optimized volumetric laser energy densities (i.e., VED of 67, 44, 31, and 35 J/mm³). As-built (AB) microstructure, grain morphology, and the recrystallization kinetics were systematically dependent on VED which generally decreases by increasing layer thickness. An increased VED led to a columnar grain morphology, strong texture, large lattice micro-strain, high fraction of low angle boundaries, and increased yield strength. Electron back scattered diffraction (EBSD) analysis revealed that also the recrystallization kinetics was significantly dependent on VED. By decreasing the VED, recrystallization was largely suppressed because of the lower dislocation density in the AB state. A processing map to study the recrystallization as a function of VED, and solution annealing temperature is proposed.