Effect of build orientation of anisotropic behavior in direct energy deposition built components

Abstract

Hybrid manufacturing integrates complementary subtractive and additive manufacturing processes into a single machine tool. Seamless integration of conventional subtractive machining and direct energy deposition (DED) allows for the production of complex, net-shape metallic components in a single manufacturing system. Hybrid manufacturing has the potential to improve repair processes and reimagine the production of new components by minimizing material waste, reducing cycle times, and expanding design flexibility. However, a major obstacle to the wide-scale acceptance of DED technology is a limited understanding of defect formation within the novel microstructures produced in DED, their relation to process parameters, and effect on resultant mechanical properties. For example, it has been shown in the literature that simple process decisions, such as changing the build orientation, can result in a 25% variation in yield strength between the vertical and horizontal orientations. In this study, the effects of layer orientation on the mechanical properties of hybrid 316L stainless steel (SS) components fabricated via a DED additive manufacturing process are investigated. Quasi-static tensile tests are conducted on “bi-metallic” wrought and DED 316L SS specimens fabricated in orientation increments of 15° with respect to the loading direction. Specimens are tested in their as-built condition without any post-process heat treatment. Young’s Modulus (E), yield strength (σYS), ultimate tensile strength (σUTS), and maximum elongation are measured, and it is found that the presence of internal defects, particularly interlayer porosity, plays a dominating role in governing many of the mechanical properties measured. In extremely low porosity components, microstructure may dominate anisotropic performance. In the presence of interlayer porosity, however, the 0° orientation is subject to lower stiffness and elongation, whereas higher angle orientations experience higher yield strength and greater ductility.