Tailored microstructure in laser-based powder bed fusion of IN718 through novel beam shaping technology

Inconel 718, processed by Laser-based Powder Bed Fusion of Metals (PBF-LB/M), exhibits epitaxial dendrite growth, leading to an anisotropic columnar microstructure. While columnar microstructures offer creep resistance, equiaxed microstructures provide more balanced mechanical properties. Understanding how to tailor the as-built microstructure in the PBF-LB/M process remains a persistent challenge. Recent advancements in beam shaping offer solutions for customizing heat flow direction in the PBF-LB/M process and tailoring the as-built microstructure. This research aims to systematically study how the laser beam shape affects anisotropy in the as-built microstructure and tensile mechanical properties. By using an inverse calculated beam shape, called as chair-shaped, the texture strength represented by J-index was reduced from 4.6 (generated by a ring-shaped beam profile with the same beam intensity and laser process parameters) to 1.37. The study prioritizes high productivity, with a building rate of 16 mm3/s (80 mu m layer thickness) across chosen process parameters compared to state-of-the-art with a build rate of 4.2 mm3/s (40 mu m layer thickness). The findings indicate that rotational asymmetric laser beam profiles with a relative beam diameter of 400 mu m significantly enhance productivity by broadening the process window. These profiles also have a profound impact on the microstructure and tensile properties compared to ring-shaped and core-ring laser beam profiles. The new microstructure features a notable reduction in grain size, elongation, and texture index, producing mechanical properties that are comparable to those of an isotropic microstructure.