Corrosion performance of wire arc additively manufactured NAB alloy

Nickel–aluminum bronzes (NAB) are vital alloys, known for biofouling resistance, crucial for marine and shipbuilding industries. This study examined corrosion performance of NAB samples fabricated by wire arc additive manufacturing (WAAM) in as-built and heat-treated conditions. Microstructural analysis revealed the WAAM-NAB parts primarily consisted of the α-phase (copper) and three types of κ-phases: κ II (spherical Fe 3 Al), κ III (Ni–Al in lamellar shape) within the interdendritic areas, and iron-rich κ IV particles dispersed throughout the matrix. In contrast, casting-produced NAB showed the formation of a rosette-like κ I phase as well. Corrosion behavior comparisons between the two NAB fabrication methods were also assessed. The microstructural characterizations revealed a rise in the size of the κ IV particles after heat-treated at 350 °C for 2 h (HT 1 ). Heat treatment at 550 °C for 4 h (HT 2 ) resulted in a needle-like κ V , coarsening of κ II , partial spheroidization of κ III , and reduced κ IV precipitation. When heat-treated to 675 °C for 6 h (HT 3 ), κ II and κ V were coarsened, κ III was completely spheroidized, and κ IV precipitation was significantly reduced. These microstructural features in HT 2 and HT 3 conditions steeply decreased their corrosion resistance compared to the WAAM as-built part. The as-built WAAM sample showed superior corrosion resistance in chloride solution, attributed to fewer κ-intermetallic phases and a finer microstructure. The κ-phases, irrespective of morphology, act as the cathodic areas versus the α-dendritic matrix, fostering microgalvanic cell formation. Consequently, precipitation of all cathodic κ-phases draws a higher galvanic current of the anodic α-phase, meaning a lower corrosion resistance.