Low-Cycle Fatigue Performance of Directed Energy Deposited and Conventionally Manufactured Hybrid Gas Tungsten Arc-Welded Duplex Stainless Steel Joints

Arc-directed energy deposition (DED-Arc) is a technology for the production of complex and large-scaled components. It benefits from high deposition rates and low investment costs. However, to further expand the applications of additively manufactured parts, the possibility for implementation in conventionally manufactured assemblies is crucial. Therefore, this study focusses on the structural integrity of welded joints of DED-Arc and as-rolled duplex stainless steels and the welded and nonwelded as-rolled benchmark. While the fraction of the constituents is almost balanced in the as-rolled condition, the amount of austenite in the DED-Arc specimens exceeds 60%. The similar weldment is predominantly ferritic and the hybrid welded joint contains ≈30% austenite, which is discussed based on the nickel concentration. Results from microstructure characterization are correlated to the superior yield and ultimate tensile strength of the as-rolled condition. Under total strain-controlled fatigue experiments, the hybrid welded joints exhibit enhanced fatigue lives at various strain amplitudes while the base material shows lowest fatigue resistance. Computed tomography and fractography conclude that the structural integrity is not governed by inherent defects, but instead the phase ratio and distribution yield significant differences in the cyclic deformation response as well as an asymmetry of the hysteretic stress–strain behavior.