Experimental investigation of corrosion-fatigue behaviour in hybrid wire arc additively manufactured parts

• Corrosion pitting significantly reduces the fatigue performance of WAAM steels. • Low life fatigue of ER70S-6 is improved when ER90S-B3 is added to the melt pool. • Due to the anisotropic nature of WAAM material orientation effects fatigue life. • Galvanic corrosion and defects affect multimaterial performance in high cycle. The rapid expansion of offshore renewable energy has driven the development of innovative manufacturing techniques to enhance the deployment, operation, and maintenance of large offshore structures. These massive installations operate under some of the harshest environmental conditions on the planet, where wind, wave, and tidal forces subject them to extensive fatigue cycles and restrict repair opportunities due to limited weather windows. Combined with continuous exposure to a corrosive marine environment, these factors accelerate corrosion–fatigue processes, which can significantly reduce the service life of offshore components. In this study, Wire Arc Additive Manufacturing (WAAM) was employed to fabricate steel wall specimens using ER70S-6 and a multi-material composition of ER70S-6 and ER90S-B3 in an 80%/20% ratio. WAAM presents a promising approach for producing complex structural components and for enabling near-site repair strategies that can reduce fabrication times and logistical challenges. From these manufactured walls, tensile and fatigue specimens were extracted to determine the mechanical performance of the materials. Fatigue specimens were exposed to seawater for 0, 2, and 4 months to induce varying levels of surface corrosion prior to testing, allowing assessment of corrosion effects on the fatigue life of WAAM steels in marine environments. Complementary macroscopic imaging, surface roughness analysis, and fractographic examination were conducted to characterise failure mechanisms and provide a comprehensive understanding of how corrosion influences the mechanical integrity and long-term performance of WAAM-fabricated steels. From this study it was found that with increased exposure time to corrosive environments the fatigue life of WAAM material decreases rapidly. Anisotropic behaviour was noted from the multimaterial orientations. However, both orientations showed to outperform ER70S-6 and meet DNV-RP-C203 design curves whereas the ER70S-6 did not.