Localized rapid cooling and microstructural banding in 316LSi multilayered thin wall: perspectives from the robotic wire and pulsed arc additive manufacturing (WPAAM) process

Abstract Wire Arc Additive Manufacturing (WAAM) has emerged as a competitive fabrication technique for stainless steel components in nuclear, marine, aerospace, and cryogenic sectors, owing to its low cost and high deposition rates. These industries commonly take advantage of stainless steel components, due to their great corrosion resistance and high mechanical performance, which are tied to their microstructural characteristics. Although studies have explored the microstructural evolution in Gas Metal Arc Additive Manufacturing (GMA-AM), little is known about the distinct effects of current pulsing in the Wire and Pulsed Arc Additive Manufacturing (WPAAM) variant. This study investigates the microstructure and local mechanical response of a multilayered 316LSi stainless steel thin wall fabricated by WPAAM. The deposit exhibited diverse δ-ferrite morphologies (vermicular, lacy, acicular and globular), especially at interlayer locations, where rapid cooling and arc pulsing caused localized transitions. Microstructural banding of type 1 was observed, attributed to periodic dendritic fragmentation under non-equilibrium solidification conditions. Cooling rates, estimated from dendritic arm spacing, ranged from 6.44 × 10³ K/s to 3.48 × 10² K/s. Such rates, typically found in high-energy beam processes, were achieved through precise arc modulation. Hardness variations were linked to local δ-ferrite morphology and fragmentation, with implications for performance optimization. These findings extend the current understanding of WPAAM and highlight its potential to tailor microstructural features through process control.