Influence of Transfer Modes and Process Parameters for Wire-Arc Directed Energy Deposition of Maraging 250

Wire-arc directed energy deposition (arc-DED) of maraging 250 (M250) steel is of growing interest for aerospace, tooling, and defense applications, yet systematic process characterization data remain limited. This study presents a mixed quantitative–qualitative factorial comparison of three Fronius synergic transfer modes, GMAW-CMT-Mix, GMAW-CMT-Universal, and GMAW-Pulsed-Arc, for single-bead M250 deposition across wire feed speeds of 4.45 to 8.26 m/min and travel speeds of 0.3 to 1.5 m/min. Bead geometry and process behavior are characterized using non-contact optical profilometry and destructive methods (i.e., metallographic sectioning, optical microscopy, and Vickers microhardness). The material feed rate ratio, Rwt, is introduced as a unifying process descriptor; heat input and cross-sectional area scale linearly with Rwt, while travel speed primarily governs bead height and wire feed speed primarily governs bead width. At the highest travel speed tested, GMAW-CMT-Mix and GMAW-Pulsed-Arc exhibit bead humping, rendering those conditions unsuitable, while GMAW-CMT-Universal maintains stable deposition with consistent dilution and the lowest heat input at equivalent Rwt. GMAW-CMT-Mix yielded the highest dilution and hardness. Linear regression of process responses against Rwt gives R2 exceeding 0.83 for both height and width across all modes. These results establish a characterization baseline supporting future multi-layer studies.