Characteristics and Processing of Hydrogen-Treated Copper Powders for EB-PBF Additive Manufacturing

Abstract

The fabrication of high purity copper using additive manufacturing has proven difficult because of oxidation of the powder feedstock. Here, we present work on the hydrogen heat treatment of copper powders for electron beam powder bed fusion (EB-PBF), in order to enable the fabrication of high purity copper components for applications such as accelerator components and vacuum electronic devices. Copper powder with varying initial oxygen contents were hydrogen heat-treated and characterized for their chemistry, morphology, and microstructure. Higher initial oxygen content powders were found to not only reduce surface oxides, but also reduce oxides along the grain boundaries and form trapped H2O vapor inside the particles. The trapped H2O vapor was verified by thermogravimetric analysis (TGA) and residual gas analysis (RGA) while melting. The mechanism of the H2O vapor escaping the particles was determined by in-situ SEM heated stage experiments, where the particles were observed to crack along the grain boundaries. To determine the effect of the EB-PBF processing on the H2O vapor, the thermal simulation and the validation of single melt track width wafers were conducted along with melting single layer discs for chemistry analysis. A high speed video of the EB-PBF melting was performed in order to determine the effect of the trapped H2O vapor on the melt pool. Finally, solid samples were fabricated from hydrogen-treated copper powder, where the final oxygen content measured ~50 wt. ppm, with a minimal residue hydrogen content, indicating the complete removal of trapped H2O vapor from the solid parts.

Quasi-Static Tensile Properties of Unalloyed Copper Produced by Electron Beam Powder Bed Fusion Additive Manufacturing

“…It is likely that special handling and monitoring or techniques to reduce surface oxides may be required. While the oxygen is elevated in the feedstock powder, it is within the range of recent reports for 3D-printed copper powder [ 14 , 31 , 36 ], where no AM-related study has reported oxygen values for copper powder that approach the values of C10100.…”

“…Moreover, in literature it is generally seen that oxygen content in the powder feedstock ranges from 40 wt. ppm [ 31 ] to ~2000 wt. ppm [ 36 ], and warrants for different processing conditions to be adopted.…”

“…Five builds, each containing three rectangular blocks measuring 58.5 mm × 12.7 mm × 58.5 mm, were fabricated upon an 86 mm diameter and 40 mm thick oxygen-free copper base plate using a customized Arcam A2 EB-PBF system (Software version 3.2, SP2, Arcam AB), the details of which are described by Ledford et al [ 31 ]. The nominal layer thickness was 40 µm.…”

A Review on Additive Manufacturing of Pure Copper

“…It is difficult to find the defects in additive manufacturing of complex components. These defects will affect the performance and service life of the parts, and it is difficult to detect the existence of defects with traditional nondestructive evaluation techniques [6]. Ledford et al [85] provided a new method for artificial monitoring of the SEBM additive process.…”

“…Copper and copper alloys are widely used in industry due to their excellent physical and chemical properties, such as thermal (400 W/(m•K)), electrical (58 × 10 6 S/m) and corrosion resistance properties [1][2][3][4]. However, the physical properties of copper and copper alloys are seriously affected by impure particles [5,6]. Pure copper material can avoid the influence of impure particles, thus providing more stable physical and chemical properties [7].…”