A Micro-Computed Tomography Comparison of the Porosity in Additively Fabricated CuCr1 Alloy Parts Using Virgin and Surface-Modified Powders.

Recently, the use of novel CuCr1 surface-modified powder for reliable laser powder-bed fusion (LPBF) manufacturing has been proposed, enabling a broader LPBF processing window and longer powder storage life. Nevertheless, virgin CuCr1 powder is also LPBF processable, on the condition that a high-energy density is employed. In this work, we compare two dense specimens produced from virgin and surface-modified CuCr1 powder. Furthermore, a third sample fabricated from surface-modified powder is characterized to understand an abnormal porosity content initially detected through Archimedes testing. Utilizing high-resolution micro-CT scans, the nature of the defects present in the different samples is revealed. Pores are analyzed in terms of size, morphology and spatial distribution. The micro-CT data reveal that the virgin CuCr1 dense specimen displays keyhole pores plus pit cavities spanning multiple layer thicknesses. On the other hand, the sample fabricated with the surface-modified CuCr1 powder mainly contains small and spherical equi-distributed metallurgical defects. Finally, the CT analysis of the third specimen reveals the presence of a W contamination, favoring lack-of-fusion pores between subsequent LPBF layers. The LPBF melting mode (keyhole or conductive), the properties of the material, and the potential presence of contaminants are connected to the different porosity types and discussed.

Influence of Carbon Nanoparticle Addition (and Impurities) on Selective Laser Melting of Pure Copper.

The addition of 0.1 wt % carbon nanoparticles significantly improved the optical absorption and flowability of gas-atomized copper powder. This facilitated selective laser melting (SLM) by reducing the required laser energy density to obtain 98% dense parts. Moreover, the carbon addition led to an in situ de-oxidation of the copper parts during the SLM process. The properties of the as-built copper parts were limited to a tensile strength of 125 MPa, a ductility of 3%, and an electrical conductivity of 22.7 × 106 S/m, despite the advantageous effect of carbon on the powder characteristics and SLM behavior. The modest mechanical properties were associated with the segregation of carbon nanoparticles and other impurities, such as phosphorus and oxygen along grain boundaries of epitaxially grown grains. Whereas, the low electrical conductivity was mainly attributed to the phosphorus impurity in solid-solution with copper.