Gas-flow-controlled porosity engineering in DED-LB and its influence on the mechanical response of 15CDV6 steel

Laser Beam Directed Energy Deposition (DED-LB) enables the fabrication of complex metallic components; however, controlling porosity remains a key challenge for functional and load-bearing applications. This work presents a design-oriented approach for the controlled generation of porosity in DED-LB through deliberate manipulation of processing gas-flow conditions. Rather than treating porosity as an unavoidable defect, the study explores its intentional engineering as a microstructural feature to tailor mechanical performance. The influence of gas-flow conditions on pore-formation mechanisms is investigated using digital image processing (DIP) of the powder stream, establishing a direct relationship between particle-injection velocity and porosity generation. Porous samples are characterized using metallography and three-dimensional computed tomography (CT), providing quantitative descriptors of pore size, morphology, volume fraction, and sphericity. The mechanical implications of engineered porosity are assessed through Small Punch Testing (SPT). Results show a progressive degradation of mechanical response with increasing porosity, driven primarily by the emergence of larger and less spherical pores that promote early damage localization and crack initiation, rather than by porosity fraction alone. Low- and medium-porosity conditions retain higher load-bearing capacity and energy absorption, while high-porosity conditions exhibit reduced mechanical performance due to large, irregular defects.