Strongly Out-of-Equilibrium Columnar Solidification During Laser Powder-Bed Fusion in Additive Manufacturing

Laser-based additive manufacturing offers a promising route for 3D printing of metallic parts. We evidence experimentally a particular columnar solidification microstructure in a laser-powder-bed-fusion-processed Inconel 718 nickel-based alloy, which we interpret using phase-field simulations and classical dendritic growth theories. Owing to the large temperature gradient and cooling rate, solidification takes places through dendritic arrays wherein the characteristic length scales, i.e., tip radius, diffusion length, and primary spacing, are of the same order. This leads to a weak mutual interaction between dendrite tips and a drastic reduction of side branching. The resulting irregular cellular like solidification pattern then remains stable on time scales comparable to the complete melt pool solidification, as observed in the as-built material.