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.

The use of 3D printed stainless steel requires a deep knowledge of its mechanical properties. This paper presents material characterisation of 316LSi austenitic stainless-steel coupons manufactured by CMT-WAAM, considering different deposition directions. The specimens were tested according to ISO 6892-1, the fractures surfaces were examined by SEM for machined and as-built conditions. The material was subject to hardness test and deep microstructural analyses, to assess the anisotropy in material properties at the micro and macro scales, respectively. A thermal analysis performed by infrared thermography of the material deposition in CMT-WAAM was also performed to establish the influence of the temperature evolution (versus time and position) on the microstructural and mechanical properties of the deposited walls. Finally, a statistical assessment was carried out, including results available in the literature and a material model available in the literature was adjusted to the test results, enabling to conclude that it is possible of accurately reproducing the uniaxial stress-strain behaviour, therefore providing a necessary input for the design of steel structures with 3D printed stainless steel.

This paper analyses the microstructural and mechanical properties of carbon steel coupons produced by CMT-WAAM. The strategy adopted in the fabrication of the test specimens using a robotised facility is explained. Then, the results of the mechanical characterization performed using as-built and machined samples, extracted in several directions (0°, 45°, 90°) relative to the material deposition trajectory, are analysed. The yield and ultimate tensile strengths were determined by performing tensile tests and the Young's modulus was determined using ultra-micro hardness measurements. A deep microstructural characterization was also performed by optical microscopy for establishing a direct relationship between the manufacturing procedures and the registered mechanical properties. The failure micro-mechanisms associated with the building orientation and the surface condition was also examined by scanning electron microscopy. It was found out that the additive manufactured material has isotropic tensile properties, which result from the formation of an annealed microstructure upon cooling from the successive CMT-WAAM thermal cycles. The machined specimens exhibit higher strength and ductility than the as-built ones. The fracture surfaces of both machined and as-built coupons showed ductile failure. The results of the uniaxial tensile tests indicate that the machined and as-built WAAM steel walls satisfy the requirements of a structural steel grade as specified by Eurocode 3.