Orientation Effects on Fatigue Behavior of Additively Manufactured Stainless Steel

Direct energy deposition (DED) is an additive manufacturing process that can produce complex near-net shape metallic components in a single manufacturing step. DED additive manufacturing has the potential to reduce feedstock material waste, streamline manufacturing chains, and enhance design flexibility. A major impediment to broader acceptance of DED technology is limited understanding of defect populations in the novel microstructures produced by DED and their relationship to process parameters and resultant mechanical properties. A design choice as simple as changing the build orientation has been observed to result in differences as great as ∼25% in yield strength for type 304L austenitic stainless steel deposited with otherwise identical deposition parameters. To better understand the role of build orientation and resultant defect populations on fatigue behavior in DED 304L, tension-tension fatigue testing has been performed on circumferentially notched cylindrical test specimens extracted from both vertical and horizontal orientations relative to the build direction. Notched fatigue behavior was found to be strongly influenced by the manufacturing defect populations of the material for different build orientations.