Abstract
Wire arc additive manufacturing (WAAM) is increasingly being considered for large marine components because it offers design flexibility, reduced material waste, and potential benefits for manufacturing cost. However, the fatigue and fracture performance of WAAM materials in seawater remains insufficiently established for safety-critical applications such as marine propellers. This study evaluates the corrosion fatigue and fracture behavior of WAAM-manufactured 316L/316LSi austenitic stainless steel intended for propeller applications. A propeller-representative WAAM component was manufactured using gas metal arc welding, and fatigue specimens were extracted in both the weld and build directions. Axial fatigue testing was performed mainly in artificial seawater at stress ranges of 200, 250, 280, 300, and 330 MPa, with a test frequency of 5 Hz and a run-out criterion of 1 × 106 cycles. Chemical composition, ferrite prediction, hardness, Charpy impact behavior, S–N response, and SEM/EDS fractography were assessed to evaluate the impact on structural integrity. The deposited material showed a chemical composition consistent with 316L/316LSi stainless steel and an estimated ferrite content of approximately 8%, indicating a generally sound austenitic weld–metal microstructure. Several specimens reached run-out at stress ranges up to 250–300 MPa, whereas valid gauge-section fatigue failures occurred in higher stress ranges. Premature failures outside the gauge section were attributed to fixture-related effects and were not considered representative of intrinsic material behavior. SEM/EDS examination of a valid fatigue fracture identified an aluminum- and oxygen-rich crack-initiation feature consistent with an aluminum oxide inclusion. This observation indicates that the fatigue response of WAAM 316L/316LSi should be interpreted not only based on stress-life data but also using principles of fracture mechanics and damage tolerance, where surface or near-surface discontinuities may act as initial flaws and promote ΔK-driven crack growth in seawater. The results demonstrate promising fatigue performance within the experimentally validated range, but they also show that bulk mechanical properties alone are insufficient for qualifying WAAM propeller components. For the investigated WAAM process route, specimen surface conditions, stress ratio (R = 0.053), artificial seawater environment, and experimentally validated cycle range of up to 1 × 106 cycles, a preliminary engineering stress-range limit of Δσ = 200 MPa is recommended for pilot applications. This value should not be interpreted as a general design limit and should not be extrapolated to other WAAM processes, geometries, surface conditions, environments, stress ratios, or service-life regimes without additional qualification testing. Further high-cycle fatigue testing, mean-stress correction, fatigue crack-growth testing in seawater, fracture-toughness assessment, realistic defect-size characterization, non-destructive testing correlation, and component-scale validation are required before broader class acceptance of WAAM-manufactured propeller components.