Copper's strong tendency to oxidation presents significant challenges for powder-binder interactions, green-part dimensional stability, and the microstructural integrity of sintered components when unbound powder is reused in Binder Jet Printing (BJP). This study investigates the effects of repeated powder reuse on the surface chemistry of copper particles and the resulting consequences for dimensional stability and microstructural evolution. Virgin copper powder (C0T) is compared with material subjected to five consecutive cure-reuse cycles under identical printing conditions. The results demonstrate that oxidation-induced surface chemistry changes progressively increase particle hydrophilicity, enhanced binder spreading and resulted in bleeding, barreling, and geometric distortion defects. Minor shifts in particle size distribution and improved apparent density and flowability after the first reuse cycle were observed. However, cumulative oxygen and carbon uptake increasingly hindered densification as the material transitioned from C0T to extensively reused powder states. Quantitative wetting measurements revealed a reduction in binder imbibition time from 0.4 s for the virgin powder (C0T) to 0.3 s after five reuse cycles (C5T), accompanied by a decrease in the binder contact angle from 116° to 96°. While reused powders produced higher green densities, their sintered densities deteriorated with increasing reuse cycles due to oxidation-driven microstructural degradation and the development of interlayer porosity. Overall, sintered density decreased by approximately 7% from C0T to C5T, with the microstructure evolving toward larger, more irregular, and increasingly interconnected interlayer pores. Hardness decreased progressively from C0T to C5T, with the highest hardness values in all conditions consistently measured along the build direction (Z). • Binder Jet Printing (BJP) and sintering of DirectPowder™ copper with irregular, non-spherical morphology was investigated using both virgin and multiple cured powder conditions. • Powder reuse improves apparent density and flowability after the first cycle, but cumulative oxygen and carbon uptake degrade sintering behavior. • Powder-binder interaction is identified as a governing mechanism controlling print fidelity and densification in binder jet printed copper. Repeated low-temperature curing induces progressive oxidation that alters copper surface chemistry and increases powder hydrophilicity. Binder imbibition time decreases and contact angle declines with increasing reuse cycles, evidencing enhanced capillary-driven binder transport. • Oxidation-driven changes in wettability accelerate binder spreading, leading to bleeding, barreling, and green-part distortion under unchanged printing parameters. • Despite higher green density, reused powders yield lower sintered density due to oxidation-induced interlayer porosity and microstructural degradation. Mechanical performance deteriorates with powder reuse, correlating reduced hardness and densification with increased oxygen and carbon content.
Khorasani et al. (Wed,) studied this question.