# Characteristics and Processing of Hydrogen-Treated Copper Powders for EB-PBF Additive Manufacturing
## 3 Results
### Electron Beam Fabrication
To determine the extent at which H\({}_{2}\)O is released from hydrogen-treated copper powders during melting as a function of the initial oxygen content, single layer discs were fabricated from each of the treated and untreated powder conditions. Figure 13A shows an image of the melted wafers on the OFE copper fixture after removal from the EB-PBF system. Figure 13C shows an optical image of the surface of the hydrogen-treated LO-Cu melted disc, which exhibits a uniform surface texture with evenly spaced melt pools. However, a non-uniform surface texture is observed on the hydrogen-treated  
Figure 12: Contour plot of the temperature profile in the XZ plane during melting, with a 2000 \(\upmu\)m hatch spacing, showing SEM images of particles located at the edge/wall (**A**), \(\sim\)0.1 mm (**B**), and \(\sim\)0.3–0.5 mm (**C**) from the wafer. HO-Cu melted disc, where exposed powder can be seen in circular pores on the surface (Figure 13B). The oxygen and hydrogen content of the starting powder, and the resulting solid discs are tabulated in Figure 13D for the treated powders. The untreated powders showed no change in oxygen content. A minimal change in the oxygen content was detected in the treated LO-Cu solid discs from the starting powder. However, the MO-Cu and HO-Cu solid discs show an approximately 50% reduction in the oxygen content from the starting powder. In both cases, a reduction in the hydrogen content is also observed as being approximately proportional to the amount of reduction in the oxygen content. The residual gas analysis was measured as a function of time during the EB-PBF of HO-Cu, MO-Cu, and LO-Cu single layer discs, and is shown in Figure 14. Each disc was melted as a single step and the H\({}_{2}\)O partial pressure was allowed to stabilize before moving to the next step. The HO-Cu and MO-Cu powders show an increase in partial pressure of the H\({}_{2}\)O vapor during the melting of the disc with the intensity of the peak being indicative of the relative amount of hydrogen in the powder, as seen in Table 1. The peaks gradually diminish as the H\({}_{2}\)O vapor is removed from the system via the vacuum pumps. A minimal peak is witnessed during melting for the LO-Cu powder because of the absence of appreciable H\({}_{2}\)O vapor trapped in the particles. The presence of porosity on the surface of the discs produced from hydrogen-treated HO-Cu and MO-Cu powder is indicative of excessive spatter, and suggests that a portion of the H\({}_{2}\)O vapor escapes from the liquid copper, in addition to the cracking mechanism observed in both the EB-PBF wafer tests and the heated stage experiments. To examine this possibility, high speed imaging (30 kfps) was conducted during the melting process. Full videos are included as part of the Supplementary Materials in this report. Selected frames of high-speed footage of the EB-PBF of hydrogen-treated LO-Cu powder (Figure 15) show a relatively stable melt pool with minimal spatter. However, Figure 16 shows selected frames from the high-speed footage of hydrogen treated HO-Cu particles during melting, and in this case, significant spatter is observed, caused by the escape of H\({}_{2}\)O vapor and the expansion in the molten copper. Large bubbles, on the order of 1-2 mm in diameter, are observed expanding and collapsing from liquid copper several mm behind the EB spot. Figure 16B shows a bubble forming in the molten pool, which then collapses and ejects molten metal from the pool shown, in Figure 16C (indicated by arrows). Figure 13: Photograph showing the oxygen free electronic (OFE) copper mixture after EB-PBF of single layer discs on top of hydrogen-treated powder cakes (**A**). Optical microscope images of the surface of single layer disc produced with hydrogen-treated HO-Cu showing pitting and porosity (**B**), and surface of single layer disc produced with hydrogen-treated LO-Cu, showing a smooth surface texture (**C**).