# Characteristics and Processing of Hydrogen-Treated Copper Powders for EB-PBF Additive Manufacturing
## 3 Results
### Powder Characterization
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Powder ID** & **Condition** & \begin{tabular}{c} **Average** \\ **O\({}_{2}\) (wt. ppm)** \\ \end{tabular} & \begin{tabular}{c} **Standard** \\ **Deviation (wt. ppm)** \\ \end{tabular} & \
\begin{tabular}{c} **Average** \\ **H\({}_{2}\) (wt. ppm)** \\ \end{tabular} &
\begin{tabular}{c} **Standard** \\ **Deviation (wt. ppm)** \\ \end{tabular} \\ \hline \hline LO-Cu & Untreated & 226.51 & 11.36 & 0.87 & 0.56 \\ (15–53 um) & Hydrogen Treated & 54.76 & 8.34 & 1.56 & 0.97 \\ \hline MO-Cu & Untreated & 462.17 & 18.87 & 1.81 & 0.66 \\ (15–53 um) & Hydrogen Treated & 282.33 & 3.79 & 31.83 & 2.02 \\ \hline HO-Cu & Untreated & 1507.33 & 12.70 & 1.95 & 0.99 \\ (15–53 um) & Hydrogen Treated & 586.97 & 35.28 & 76.44 & 5.77 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical content of copper powders. Figure 5: Plot showing at. % oxygen versus at. % hydrogen for all of the hydrogen heat-treated copper powders used in this study. Figure 6: Plot showing the skeletal density of the untreated and hydrogen heat-treated copper powders of varying initial oxygen content, as measured by helium pycnometry. Figure 7: Representative low and high magnification scanning electron micrographs of untreated and hydrogen-treated MO-Cu powder. (**A**) Low magnification and (**C**) high magnification of untreated hydrogen-treated MO-Cu powder; (**B**) Low magnification and (**D**) high magnification of hydrogen-treated MO-Cu powder. The representative particles were serial sectioned using a FIB to reveal the internal structure of the untreated and hydrogen-treated powder of each type using ion channel imaging, as shown in Figure 8. Figure 8A is an ion image of a sectioned untreated LO-Cu particle showing no obvious porosity or oxide-rich particles. Figure 8B,C are cross-sectioned MO-Cu and HO-Cu particles, respectively, which have fine equiaxed microstructures and submicron oxygen-rich particles along the grain boundaries. The distribution of oxide particles along the grain boundaries vary by size, where larger oxides tend to be located at triple points, and smaller oxides along the grain boundaries. Figure 8D shows a hydrogen-treated LO-Cu particle with minimal change after hydrogen treatment because of its initially low oxygen content. The LO-Cu particles, produced with a special handling consideration, consistently showed few to no internal oxides (within the resolution of the instrument). A grain boundary is shown in Figure 8A,D. However, the lack of contrast between the two grains can be attributed to the similarity of the grain orientations. Figure 8E shows a hydrogen-treated MO-Cu particle with both a micron and submicron scale porosity throughout the grain boundaries. The high oxygen content of the HO-Cu particle leads to the formation of a significant interconnected porosity at the grain boundaries after hydrogen heat treatment. Several large pores are evident after hydrogen treatment in Figure 8E,F for MO-Cu and HO-Cu, respectively; however, in both cases, small dark features are evident along the grain boundaries. It was not immediately clear from this SEM analysis whether these were residual, unreacted oxides or small water vapor induced pores. Videos of the serial sectioning process using FIB are provided in the Supplementary Materials for each of the cases in Figure 8. The HAADF STEM imaging and EDS (Figure 9) of a grain boundary triple point of hydrogen heat-treated MO-Cu confirms the presence of the H\({}_{2}\)O vapor induced porosity, consistent with the observations of [PERSON] and [PERSON] [28; 30]. Figure 8: Representative high magnification ion channeling contrast micrographs of pretreated LO-Cu (**A**), MO-Cu (**B**), HO-Cu (**C**), and post hydrogen treatment LO-Cu (**D**), MO-Cu (**E**), and HO-Cu (**F**) focused ion beam (FIB) sectioned Cu powder particles showing the presence of grain boundary Cu\({}_{2}\)O in the untreated condition (**A–C**), which reacts with hydrogen to form H\({}_{2}\)O pores (**E,F**).