Corrosion analysis of plasma arc welded and gas metal arc welded 316L stainless steel in wire arc additive manufacturing

Wire arc additive manufacturing (WAAM) is an emerging technology for fabricating metallic components with high deposition rates and cost efficiency. However, the microstructural characteristics and corrosion resistance of WAAM fabricated materials require thorough investigation to ensure their suitability for demanding applications. This study analyzes the microstructure and corrosion resistance of 316L austenitic stainless steel produced using two different WAAM processes, gas metal arc welding (GMAW) and plasma arc welding (PAW). Microstructural analysis reveals an austenitic matrix with δ-ferrite dispersed in various morphologies throughout the structure. In each deposited bead, ferrite transitions from a fine columnar dendritic structure near the fusion line to coarser columnar structures with more widely spaced secondary dendrites. The PAW sample shows higher microhardness values than the one manufactured with GMAW. Electrochemical corrosion tests in a saline solution show that despite the significant amount of ferrite formed during the additive process, WAAM-processed 316L exhibits comparable or even improved corrosion resistance relative to the original filler wire, with a wider passive range and a more positive pitting potential. Due to the better control of the process and the consequently lower number of defects produced, the 316L fabricated via PAW presents a higher pitting potential than its GMAW counterpart, resulting in a more stable passive film and increased resistance to localized breakdown.