Thermal, microstructural, and mechanical characterization of early-stage deposition in wire arc additive manufacturing

This study investigates the evolution of process conditions, microstructure, and mechanical properties during multi-layer wire arc additive manufacturing (WAAM), focusing on initial layers. Using a multi-sensor approach with electrical signal analysis, infrared thermography, and microstructural characterization, we examined dynamic changes during the deposition of up to 20 layers of low carbon steel (1.00-mm wire) on a 3.3-mm substrate under constant parameters (26 V, 250-mm/min deposition speed, 7-mm/s wire feed rate). Our findings reveal that peak temperatures increased by 300 °C (from ~ 1600 °C to ~ 1900 °C) with layer count, stabilizing after 6 layers due to reduced heat diffusion to the substrate. Concurrently, electrical current decreased by approximately 10% after the first 4 layers, reducing power from 2.40 kW to 2.15 kW. Microstructural analysis showed a transition from radially oriented grains in initial layers to enlarged, equiaxed grains (7–10 μm) in subsequent layers, while top layers consistently exhibited smaller, vertically oriented grains (2–4 μm). Microhardness measurements revealed a “saddle” profile, decreasing in lower layers (from ~ 200 HV to ~ 150 HV) as more layers were added and stabilizing after about 4 layers, with top layers consistently showing the highest microhardness (~ 250 HV). U-shaped deposition paths resulted in ~ 60 °C higher peak temperatures compared to straight paths, but these preheating effects were limited to the first three layers. Notably, the influence of new layer deposition on microstructure and properties was confined to approximately 8-mm depth. These insights contribute to optimizing WAAM technology for enhanced component quality across various industrial applications.