Microscopic characterization of oxygen content accumulation and powder recyclability in selective electron beam melting of copper

In this study, the oxygen content accumulation and powder recyclability in selective electron beam melting (SEBM) of copper were systematically investigated using standard characterization and image recognition techniques. The behavior of recycled copper powder morphology across different recycling cycles was characterized through scanning electron microscope (SEM) with assistance of image recognition, revealing that dendritic surface features gradually disappear, surface roughness intensifies, and the proportion of non-spherical particles increases, leading to reduced flowability and bulk density. Quantitative analysis confirmed that oxygen content rises with recycling cycles, reaching 0.4341 wt.% after 12 cycles, while energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) indicated changes in powder properties. The oxides in the SEBM-fabricated copper were identified as uniformly dispersed copper oxide particles approximately 50 nm in size, via transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), without evidence of segregation at grain boundaries. Despite the oxygen accumulation, mechanical properties-including yield strength, tensile strength, and elongation-remained relatively stable, with only a slight 2.67% increase in ultimate tensile strength, attributed to dispersion strengthening mechanisms. However, electrical conductivity decreased by 3.81% at the highest oxygen content, due to electron obstruction by oxide impurities. This research clarifies the correlations between powder recycling, oxygen content, and material properties in SEBM copper, providing insights for optimizing recycling strategies.