Development and Testing of 316L Stainless Steel Metal Additive Manufacturing Test Articles for Powder Bed Fusion and Directed Energy Deposition Processes

Abstract

The advancement of metal additive manufacturing (AM) technologies provides opportunities for novel part design and improved manufacturing capability compared with parts fabricated using wrought or cast materials. Heterogeneous microstructures and anisotropic material properties complicate the application of this technology to critical components. In this study, metal AM test article builds were designed for powder bed fusion (PBF) and directed energy deposition (DED) processes. The PBF test article build was designed to evaluate the effects of specimen orientation, thickness, surface condition, and build volume location on tensile properties. This build design was tested using the laser (L)-PBF process with 316L stainless steel. The L-PBF builds involved the fabrication of as-built tension test specimen geometries with variations in thickness and orientation to accurately represent the surface finish and microstructure that exist in parts with features of these sizes and orientations. Variability in tensile properties for the L-PBF test article builds were correlated with specimen orientation and thickness; differences in surface condition were correlated with tensile property variability in thin specimens but not in thicker specimens. The DED test article build was designed to evaluate the effects of specimen orientation and build feature thermal history and was tested using the electron beam (EB)-DED process with 316L stainless steel. Some tensile property variability related to build feature type was identified in the EB-DED builds, but other phenomena in the builds affected variability, including incomplete fusion defects and the formation of a detrimental, secondary sigma phase. The results demonstrated the need for a thorough evaluation and understanding of the numerous factors that affect the properties of metal AM parts. The build design concepts tested can demonstrate the effects of such factors on metal AM mechanical properties and provide a framework for a qualification schema that accounts for potential sources of variability affecting AM material performance.