Enabling overhang fabrication in directed energy deposition using removable supports: Thermal behavior and down-skin surface formation

Directed energy deposition (DED) offers advantages for repair and remanufacturing; however, fabrication of overhang structures remains challenging due to unstable melt pool behavior and insufficient support conditions. In this study, a Cu removable support structure was introduced to enable the fabrication of overhang geometries during the DED process. Single-point thermocouple measurements at a fixed location indicated geometry-dependent differences in the support-side thermal response during deposition. Compared with the hollow configuration, the solid support exhibited a more buffered support-side thermal response at the fixed measurement location, which was associated with improved down-skin surface quality and stable formation of planar overhang structures without macroscopic collapse. Inclined overhang specimens fabricated at angles between 20° and 50° also showed no macroscopic collapse, while the down-skin surface roughness exhibited a minimum at approximately 40°. The higher roughness at low angles was associated with the stair-stepping effect caused by increased layer height projected onto the inclined surface, whereas the roughness increase at higher angles was associated with localized Fe-based surface protrusions related to particle attachment and/or re-solidified material. Compositional analysis showed no evidence of a continuous Cu-rich interfacial layer or an extensive interdiffusion zone between the deposited H13 and the Cu removable support. Line EDS of the exposed down-skin surface after support removal further revealed localized Cu spikes rather than a continuous Cu distribution. These results indicate that Cu removable supports can facilitate overhang fabrication in DED while maintaining chemically limited support–deposit interaction and controllable surface quality under the present conditions.