# Characteristics and Processing of Hydrogen-Treated Copper Powders for EB-PBF Additive Manufacturing
## 3 Results  
### Powder Characterization  
The oxygen and hydrogen content were carefully tracked after the atomization, screening, and hydrogen treatment. Table 1 shows the oxygen and hydrogen content for the untreated and hydrogen treated LO-Cu, MO-Cu, and HO-Cu screened powders. The LO-Cu powder was procured as-atomized and was sieved in-house under argon in order to maintain a low oxygen content of ~225 wt. ppm and ~1 wt. ppm hydrogen. After the hydrogen treatment of the LO-Cu powder, the oxygen content was reduced to ~50 wt. ppm, with minimal change in the hydrogen content. The untreated MO-Cu powder contained ~450 wt. ppm oxygen and ~2 wt. ppm hydrogen, and after hydrogen treatment, the oxygen content was reduced to ~280 wt. ppm, but the hydrogen content increased to ~30 wt. ppm, indicating that the hydrogen was retained within the powder after treatment, likely as trapped H\({}_{2}\)O, which is consistent with the reported literature by [PERSON] and [PERSON] [28; 30]. As a third condition, the HO-Cu was intentionally oxidized in order to exaggerate the effects of oxygen, and produced an extreme condition with oxygen measured at ~1500 wt. ppm and ~2 wt. ppm hydrogen. After the hydrogen treatment of the HO-Cu powder, the oxygen content was reduced to ~580 wt. ppm, but the hydrogen content increased to ~75 wt. ppm, again most likely trapping H\({}_{2}\)O inside the particles. No significant sintering is observed after the powders undergo the hydrogen treatment. Figure 5 shows a plot of the atomic percent of oxygen versus the atomic percent of hydrogen for all of the hydrogen heat-treated copper powders used in this study. The 2:1 stoichiometric relationship is a key indicator that hydrogen is retained in the powder in the form of H\({}_{2}\)O vapor. It is also notable that the linear relationship is offset by \(-\)0.06% at. % oxygen, which can be accounted for volumetrically on the surface of the powder particles. Further evidence for the formation of H\({}_{2}\)O vapor induced cavities in the powder is supported by the helium pycnometry results for each powder condition (shown in Figure 6). No significant change in density is seen after the hydrogen treatment of the LO-Cu particles from the untreated condition. Without internal, grain boundary Cu\({}_{2}\)O, the hydrogen does not react to form H\({}_{2}\)O vapor. However, both the MO-Cu and HO-Cu particles show a decrease in density after hydrogen treatment, which is likely caused by the formation of H\({}_{2}\)O in the particles due to the significant difference in densities between H\({}_{2}\)O (1 g/cm\({}^{3}\)) and copper (8.96 g/cm\({}^{3}\)). The decrease in density among the as received powders can be attributed to the increasing contribution of Cu\({}_{2}\)O with the increasing oxygen content, which has a density of only \(-\)6 g/cc. Because of its relatively high oxygen content, the MO-Cu powder was selected to observe the effect of hydrogen heat treatment on the surface oxides. Figure 7 shows the representative low and high magnification scanning electron micrographs of (Figure 7A,C) and the hydrogen-treated (Figure 7B,D) MO-Cu powder. Figure 7C shows the surface of the untreated MO-Cu powder, where bright spots were identified as oxygen-rich copper particles. Figure 7D shows the surface at the same magnification after the hydrogen treatment of the MO-Cu powder, where the surface oxides have been largely removed. These results were typical for untreated and hydrogen-treated MO-Cu and HO-Cu particles.