# Characteristics and Processing of Hydrogen-Treated Copper Powders for EB-PBF Additive Manufacturing
## 2 Materials and Methods
### EB-PBF Processing of Hydrogen-Treated Copper Powder  
To directly observe and quantify the H\({}_{2}\)O release during EB-PBF, single layer discs were melted using the various hydrogen-treated and untreated powders. Figure 4 illustrates the experiment. The fixture upon which the experiments were carried out was an annealed OFE copper cylinder, 100 mm in diameter and 50 mm thick. Six equally spaced cylindrical pockets, measuring 25 mm in diameter by 3 mm deep were milled into the surface at a radial distance of 30 mm from the plate center, such that  
Figure 3: Illustration of the single melt track width geometry with 2.0 mm spacing. Powder was harvested from between the wafers in a serial fashion, as a function of the distance from the solid copper wall. each pocket is effectively isolated from the others, as seen in Figure 4. After the machining, the copper substrate was cleaned using a standard ultra-high vacuum (UHV) protocol for machined copper. Each of the pockets in the substrate were filled and leveled to the top surface of the plate with \(\sim\)5 grams of LO-Cu, MO-Cu, or HO-Cu powder before or after hydrogen treatment, each having a replicate. The oxygen and hydrogen content of the powder, as noted previously, was measured by inert gas fusion prior to this experiment. A type K thermocouple was affixed to the bottom of the substrate, and the substrate was placed on top of the build piston, which allows for the thermal isolation from the system. The vacuum chamber was evacuated to a pressure of 3.75 \(\times\) e\({}^{-5}\) Torr, and the copper substrate was heated by repeatedly scanning the defocused electron beam in a circular area, 25 mm in diameter at the center of the substrate, with a beam current of \(\sim\)2-4 mA. The substrate temperature was measured by the thermocouple at the bottom, and a two-color pyrometer through a sapphire window positioned in one of the upper viewports. The substrate heating was manually modulated until both of the temperature readings agreed within 5% of the target value (300 \({}^{\circ}\)C), and then this temperature was maintained for a 2 h outgassing cycle. A 200 amu residual gas analyzer (SRS-RGA200) was used to measure the partial pressure of the gas species of interest for this study (O, H, N, NO, NO\({}_{2}\), and H\({}_{2}\)O). During the outgassing cycle, the background H\({}_{2}\)0 partial pressure was observed to decrease and stabilize at \(\sim\)8 \(\times\) e\({}^{-7}\) Torr. This outgassing period at 300 \({}^{\circ}\)C also allowed sufficient time for the initial stages of sintering to take place within the powder. This was observed with the IR camera by a uniform emissivity shift across all six powder pockets. The focused electron beam was then raster scanned over an area measuring 20 mm in diameter on the surface of each one of the powder pockets. A line energy of 0.8 J/mm (600 mm/s, 8 mA, 0 mA focus offset, 100 \(\upmu\)m hatch offset) was sufficient to melt and consolidate a single layer of copper supported underneath by the sintered powder. The melting process was recorded by the thermal imaging camera through a germanium port at 25 Hz, and by in-situ monitoring of the back scattered electron signal. A  
Figure 4: Illustration of the in-situ H\({}_{2}\)O vapor out-gassing experiment. The electron beam melting (EBM) vacuum chamber is outfitted with a residual gas analysis (RGA) and IR camera, and the surface temperature is monitored by a two-color pyrometer and thermocouple (**A**). The base fixture contains six 3 mm deep pockets (**B**), which are filled with hydrogen-treated and untreated powders with varying initial oxygen content. A single layer disc is melted on the top surface of each powder type. During melting, H\({}_{2}\)O is released from the powder or melt pool, and detected by the RGA (**C**). Upon completion, the powder is manually removed from the solid disc of copper, which is analyzed for oxygen and hydrogen content by inert gas fusion (**D**). thermal video of the melting process is available in the Supplementary Materials.