Impact of Porosity on the Bending Fatigue Strength of WAAM-Fabricated Super Duplex Stainless Steel

This study explores the influence of porosity on the bending fatigue strength of super duplex stainless steel (SDSS) produced using wire arc additive manufacturing (WAAM). Cross-sectional analysis revealed that the SDSS wall, with an average width of 5.8 mm, is approximately 1 mm wider than the porous SDSS (SDSS P) wall, attributed to lower printing speeds and different shielding gases. X-ray imaging confirmed the absence of pores in the SDSS material but showed abundant, evenly distributed pores in the SDSS P material, with diameters ranging from 0.4 to 1.1 mm. Hardness measurements in the vertical direction, showed consistent levels across both materials, with average values of 312 HV for SDSS and 301 HV for SDSS P. This uniformity suggests similar base material strength when porosity is not a factor. However, mechanical testing revealed significant differences: SDSS exhibited a yield strength (YS) 15.4% higher than SDSS P (630 MPa vs. 546 MPa) and an ultimate tensile strength (UTS) of 819 MPa compared to 697 MPa for SDSS P. Most notably, SDSS showed an elongation of 37.4%, approximately 118.7% greater than that of SDSS P, indicating a significant reduction in ductility due to porosity. Fatigue testing demonstrated a fatigue limit of 377 MPa for SDSS, significantly higher than the 152 MPa limit for SDSS P. The presence of pores was found to drastically reduce the fatigue strength. Fracture analysis showed that fatigue cracks in SDSS P originated from pores. Overall, the findings demonstrate that porosity significantly diminishes the mechanical performance of WAAM-fabricated SDSS, making it less suitable for applications requiring high strength and ductility.