Characterisation of infill strategies in WAAM for solid components fabricated with ER100S-G wire

This study presents a comprehensive characterisation of infill strategies in Wire Arc Additive Manufacturing for the fabrication of thick-walled steel components using ER100S-G wire. The primary objective of this work is to systematically assess how different combinations of edge and infill deposition strategies influence the thermal behaviour, defect formation, surface quality, and resulting microstructural and mechanical properties of solid WAAM components. Eleven deposition strategies, combining edge and infill parameters under two heat input configurations, were systematically evaluated. Thermal analysis based on Δt₈₋₅ cooling times revealed significant heat accumulation in corner regions and extended deposition paths, with cooling times increasing by up to approximately threefold depending on the deposition strategy and location. Microstructural characterisation identified acicular ferrite and bainite with refined grains in faster cooling zones. Electron Backscatter Diffraction confirmed grain growth and local misorientation reduction with increased heat input, alongside a transition from low-angle to high-angle grain boundaries, indicating partial recrystallisation and microstructural recovery. Laser profilometry showed that surface height variation remained below 1 mm in all samples, yet concentric infill strategies and non-weaving conditions resulted in the most irregular surfaces, affecting dimensional precision and post-processing requirements. Defects such as pores, lack of fusion, and overlaps were more frequent in low-energy or non-weaving strategies due to poor material distribution. Finally, hardness measurements confirmed that faster cooling rates (Δt₈₋₅ < 12 s) led to higher hardness values, reinforcing the relationship between thermal history and mechanical response. Overall, the results demonstrate that infill strategy selection plays a critical role in balancing productivity, thermal stability, surface quality, and structural integrity in WAAM-fabricated solid components. These findings offer valuable insights into the process–structure–property relationships in WAAM, providing practical guidance for optimising the production of defect-minimised and structurally consistent solid steel components.