Influence of the laser power and powder feed rate on the porosity, dilution, and building efficiency of pure copper parts fabricated via directed energy deposition with a blue laser

We examined single- and multilayer formations in the directed energy deposition for manufacturing pure copper parts using a blue laser with a wavelength of 445 nm. We investigated the influence of laser power and hatching pitch on the surface quality of single-layer structures as well as evaluated the porosity and dilution of multilayer structures fabricated at various laser powers and powder feed rates using energy-dispersive X-ray spectrometry. In addition, the applicability of the simplified method based on the ratio of the built height and penetration depth to the AM process has been examined, and the predicted elemental content was compared with the results obtained from the SEM-EDS analysis. Based on these findings, a range of building conditions that reduce the dilution, suppress the porosity, and improve the building efficiency of the built parts was established. We found that a good surface quality of the single-layer structure was obtained at laser powers and hatching pitches ranging between 150 and 180 W and 0.4 and 0.5 mm, respectively. A higher laser power and a lower powder feed rate decreased the porosity and increased the building efficiency while promoting dilution with the substrate. At a laser power of 180 W and a powder feed rate of 10 mg/s, the built structure exhibited a minimum porosity of 0.1% and a maximum building efficiency of 36%. Dilution with the substrate was the lowest at a laser power of 180 W and a powder feed rate of 20 mg/s, and the proportion of Cu reached 99.0 wt% at a distance of 200 mu m from the built structure-substrate interface. The predict method of the dilution based on the ratio between the built height and penetration depth can be integrated in the AM process despite a low prediction accuracy near the substrate due to the complex mixture in the Fe-Cu system.