Location-dependent deformation behavior of additively manufactured copper and copper-carbon nanotube composite

Pure copper (Cu) and copper-carbon nanotube (Cu-CNTs) alloys were fabricated using laser powder bed fusion additive manufacturing (LPBF-AM) with a relatively high density. Their location-dependent (i.e., distance from build plate) microstructure and nanomechanical properties at room temperature were investigated. The microstructure of the as-build Cu showed ~40% lower porosity as compared to the AM Cu-CNTs. The amount of porosity was dependent on location for Cu sample with the bottom surface had ~61% lower porosity as compared to the top surface, however the change in porosity was negligible for as-build Cu-CNTs depending on the distance from the build plate. With the addition of 0.5 wt% CNTs, the mechanical properties of the composite were decreased slightly may be due to porosity, weak interfacial bonding of Cu and CNTs, CNT agglomeration, and degraded CNTs. Nanoindentation tests showed that the average modulus value and hardness of the composites were in the range of 40–80 GPa and 0.7–1.1 GPa, respectively depending on the strain rates and distance from the build plate; 18% and 25% decreases were achieved compared with pure copper, respectively. Creep displacement also increased for as-build Cu-CNTs as compared to the pure Cu. Further, for each system, increase in porosity led to increase in strain rate sensitivity and decrease in maximum creep displacement.