Investigating build orientation-induced mechanical anisotropy in additive manufacturing 316L stainless steel

Abstract

Build orientation-induced mechanical anisotropy is critical for additive manufacturing metals. To leverage the existing research on anisotropy between Z and X/Y build orientations, this work focuses on the anisotropic behavior within 2D planes. Therefore, tensile coupons of 316L stainless steel (316L-SS) were fabricated in five different build orientations (X, Y, XY45°, Z, and ZX45°) using the laser powder bed fusion process with a pulsed laser. Different characterization techniques at various length scales were employed to investigate the mechanisms of mechanical anisotropy. According to the electron back-scattered diffraction (EBSD) study, X and Y samples had a larger fraction of <001> and <110> grains, whereas XY45° coupons had a larger fraction of <111> grains along the tensile axis. In contrast, Z samples exhibited a dominant <110> texture parallel to the tensile axis. X-ray diffraction analysis revealed that all the samples had a single austenitic phase but different dislocation densities. The tensile results of all samples showed higher yield strength and comparable ductility with those in the literature. Among all the build orientations, XY45° coupons had the highest yield strength due to the large fraction of <111> grains oriented along the tensile axis and the highest dislocation density of 2.2 × 1015 m−2. In contrast, the highest ductility of Z samples was caused due to twinning-favored <110> crystallographic texture along the tensile axis. The onset and termination of different stages of strain hardening were mainly affected by the cellular sub-grain structure and crystallographic texture, as well as their interactions with dislocation generation and evolution. These findings indicated that crystallographic texture and dislocation density were the dominant contributions to the mechanical anisotropy followed by grain morphology.