Nanoparticle-enhanced absorptivity of copper during laser powder bed fusion

Laser powder bed fusion (LPBF) of pure copper for thermal and electrical applications is hampered by its low near-infrared absorptivity and high thermal diffusivity. These material properties make it very difficult to localize the thermal energy needed to produce high density 3D printed parts. Modification of metal powders via nanoparticle additives is a promising approach to increasing absorptivity, but the effect of nanoparticles on absorptivity and melting behavior during LPBF is not well understood. In this study, we developed an in situ calorimetry system to measure effective absorptivity during LPBF on copper substrates. We decorated copper substrates using three nanoparticle systems (CuS, TiB2, multilayer graphene flakes) and demonstrated an enhanced absorptivity of the decorated substrates relative to pure copper. Graphene nanoflakes resulted in the highest improved absorption relative to pure copper from 0.09 to 0.48, due to their stability at high laser scanning powers. A thermomechanical model with convective heat transfer provided confidence in the measurements by reproducing the experimental melt pool traces. Full 3D cylindrical prints demonstrated an improvement in relative density of the copper-graphene powder prints (in the range of 0.930-0.992), relative to that of as-purchased copper powder prints (in the range of 0.854-0.972). This work provides a fundamental study of nanoparticle-enabled LPBF of highly reflective metals and demonstrates a viable route for expanding the library of reliably printable metals.

Automated summary

Laser powder bed fusion (LPBF) of pure copper for thermal and electrical applications is limited by low near-infrared absorptivity and high thermal diffusivity. This study investigates the effect of nanoparticle additives on absorptivity and melting behavior during LPBF. Using an in situ calorimetry system, decorated copper substrates with three nanoparticle systems (CuS, TiB2, multilayer graphene flakes) demonstrated enhanced absorptivity compared to pure copper. Graphene nanoflakes resulted in the highest improved absorption due to their stability at high laser scanning powers. The work also showed an improvement in relative density of the copper-graphene powder prints compared to as-purchased copper powder prints.