Impact of powder properties on deoxidation and densification of carbon steels during powder bed fusion - Laser beam

This work examined the influence of powder properties on deoxidation and densification of carbon steels during powder bed fusion-laser beam (PBF-LB) at compositions between 0.06 and 1.1 wt% C. Analysis revealed that deoxidation was greatest in alloys with high carbon content, reaching losses of up to 440-600 ppm at compositions of 0.75 and 1.1 wt% C. This behavior was not due to enhanced oxygen removal by spatter, as spatter in high carbon alloys had less oxygen pickup (similar to 4% vs. similar to 27%) and formed smaller oxide layers (similar to 42 nm vs. similar to 82 nm). Instead, it was due to the high oxygen affinity of carbon at elevated temperature, which resulted in formation of gaseous carbon oxides that were subsequently removed by the process atmosphere. Regarding densification, powders with high avalanche energy (>7.75 mJ/kg), break energy (>4.75 mJ/kg), and particle size distribution (D-10 > 25 mu m) were more likely to form lack of fusion porosity at low energy input.