Modification of Electrical and Mechanical Properties of Selective Laser‐Melted CuCr0.3 Alloy Using Carbon Nanoparticles

Abstract

Herein, the influence of carbon nanoparticle addition on the selective laser melting (SLM) behavior and the resultant properties of gas‐atomized CuCr0.3 powder are investigated. The carbon addition neither affects the powder flowability, nor its packing density, but it significantly enhances the optical absorption for infrared radiation. Despite the improved optical absorption of the powder bed after carbon addition, a comparable SLM behavior is observed for both virgin and carbon‐mixed CuCr0.3 powders. Furthermore, the addition of carbon nanoparticles facilitates in situ deoxidation of copper and chromium oxides present in the CuCr0.3 powder. Accordingly, a larger fraction of chromium is obtained in its metallic form in the as‐built carbon‐mixed CuCr0.3 part. The presence of metallic chromium allows tailoring of the mechanical and electrical properties by postheat treatments (HTs). The best combination of mechanical (tensile strength of 298 ± 19 MPa, yield strength of 208 ± 18 MPa, ductility of 21 ± 4%) and electrical (87 ± 1% international annealed copper standards [% IACS]) properties is realized for the carbon‐mixed CuCr0.3 alloy after a direct age hardening HT. The improvement in mechanical properties is attributed to the precipitation of nanometer‐sized, coherent, and metallic chromium precipitates in the copper matrix.

Surface Modified Copper Alloy Powder for Reliable Laser-based Additive Manufacturing

“…Hence, the surface-modified CuCr1 powder demonstrates improved powder storage life by minimizing its natural oxidation. Lower oxygen content in the initial CuCr alloy powder is beneficial for tailoring the mechanical properties of the fabricated parts by post-heat-treatments [25]. The oxygen pickup of both powders after twelve months of unprotected storage at room temperature.…”

“…However, the melt pool stability could not be maintained along the complete melt track due to the segregation of carbon nanoparticles along the melt pool borders. Consequently, no significant difference in the LPBF behavior, between the virgin CuCr0.3 and carbonmixed CuCr0.3 powders, was observed [25]. Hence, the current state-of-the-art technology cannot offer a reliable (safe, consistent, flexible, and low energy consumption) fabrication of dense, highlyconductive copper parts.…”

“…Since upgrading the LPBF machine with a green or blue laser to process pure copper is not always economically or technologically feasible, some authors have evaluated the use of pre-alloyed, gas-atomized copper powder with a small amount (< 1wt.%) of alloying elements, such as chromium and zirconium [22][23][24][25]. However, this is still not a sustainable approach, since the alloying element is distributed uniformly within the copper powder particles, and thus, the pre-alloyed copper powders exhibit similar laser reflectivity values as pure copper.…”

“…Hence, comparable LPBF processing behavior is expected [26]. Accordingly, rather dense copper parts could only be obtained within a narrow LPBF processing window, provided that a combination of fine particles (D50: ~20 µm), thin powder layers (≤ 20 µm), low laser scan speeds (200-400 mm/s), and high laser power values (>350 W) are employed [8,[23][24][25]. Moreover, the fabrication of copper parts at a low laser scan speed (low productivity) requires a high laser scan time per layer.…”

“…Thus, an altered LPBF behavior and concomitant variation in part density and performance could be obtained [27]. As an alternative approach, surface modification of copper powder by the addition of carbon nanoparticles for improving the powder optical absorption has been evaluated [14,25]. The use of carbon-mixed copper powder exhibiting a high optical absorption of 56-67% could have assisted in the formation of a stable melt pool at the start of each melt track.…”