Mixing of Spherical Solid and Nanoporous Copper Powders As Low-Reflectance Feedstock for Laser Powder Bed Fusion

Abstract

Abstract Micro- and nanoporous materials have gathered attention from the scientific community due to their size dependent properties, including but not limited to high specific surface area, surface diffusivity, bulk diffusivity and permeability, catalytic activity, and distinct optical properties. In this work, spherical nanoporous copper (np-Cu) powders, due to their nanosized porosity and low Cu2O content, show hemispherical total reflectance of 20% which is significantly lower than its bulk counterpart value for solid or molten copper of approximately 97% at wavelengths of most commercial Laser Powder Bed Fusion (L-PBF) commercial machines. The low-reflectance of np-Cu powders has the potential to be used in L-PBF to improve laser absorption, volumetric energy efficiency, and throughput of this additive manufacturing process. In fact, a prepared mixture of solid Cu powders containing only 5 wt.% of np-Cu powders reflects 34.8 % less than pure copper powders as shown in this paper. Np-Cu powders are fabricated via chemical dealloying of gas atomized CuAl alloy in a robust and scalable approach, and then mixed with pure copper powders to prepare hybrid feedstocks. Under this framework, the crucial role of deglomeration strategies to achieve homogeneity and flowability of np-Cu/Cu hybrid mixtures are evaluated via particle imaging to determine agglomerate size and composition with an eye at obtaining a high-quality print in L-PBF. In np-Cu powders fabrication, washing them in low-surface tension fluids upholds the highest degree of deglomeration in their fabrication process, and for hybrid feedstocks preparation, pre-mixing Cu and CuAl prior to dealloying yields the best homogeneity results with smallest size of agglomerates and good flowability.