In this article, the laser-based powder bed fusion ( L -PBF) processing behavior of pure copper powder is evaluated by employing a conventional infrared fiber laser with a wavelength of 1080 nm, a small focal spot diameter of 37.5 µm, and power levels up to 500 W. It is shown that bulk solid copper parts with near full density (ρ Archimedes = 99.3 ± 0.2%, ρ Optical = 99.8 ± 0.1%) can be produced using a laser power of 500 W for the chosen combination of powder particle size, L -PBF settings, and pure copper baseplate. Moreover, at 500 W, parts with a relative density exceeding 99% are manufactured within a volumetric energy density window of 230–310 J/mm3, while laser power levels below 500 W did not produce parts with a relative density above 99%. An analytical model is used to elucidate the L -PBF processing behavior, wherein both conduction and keyhole regimes corresponding to the employed L -PBF settings are identified. The analytical model-based results predict that the bulk solid copper parts with near full density are produced in a keyhole regime prior to the onset of keyhole-induced porosity, which is in accordance with the porosity types observed in the parts. The L -PBF fabricated copper parts exhibit an electrical conductivity of 94 ± 1% compared to the international annealed copper standard (IACS) and demonstrate a tensile strength of 211 ± 4 MPa, a yield strength of 122 ± 1 MPa, and an elongation at break of 43 ± 3% in the as-built condition.

Laser-based powder bed fusion additive manufacturing of pure copper

Laser powder bed fusion additive manufacturing of highly conductive parts made of optically absorptive carburized CuCr1 powder

CuCrZr is a precipitation hardening alloy, used for its good electrical and thermal properties combined to high mechanical properties. Using additive manufacturing technologies, and more specifically the laser powder bed fusion (L-PBF) process, allows designing highly complex parts such as compact and efficient CuCrZr heat exchangers. Additional understanding of the specific CuCrZr metallurgy during this manufacturing process is still needed to fully take advantages of these possibilities. This work aimed (i) to clarify the impact of the L-PBF process and post-fabrication heat treatments on the microstructure of L-PBF CuCrZr alloy, (ii) to determine the corresponding mechanical and electrical properties and (iii) to quantify the contributions of the different nano-scale strengthening mechanisms (nano-precipitation, dislocations, solid solution, grain size refinement) depending on the different heat treatments. The microstructures of the CuCrZr samples are carefully analyzed at different scales thanks to scanning electron and transmission electron microscopy, highlighting the effect of the different heat treatments. In all heat-treated samples, Cr nano-precipitates are uniformly dispersed in the Cu matrix; few Zr nano-precipitates are observed either at grain boundaries, next to Cr nano-precipitates, or inside the Cu matrix. Moreover, the mean grain size, dislocation density, mean radius and volume fraction of the Chromium nano-precipitates are measured. These data are introduced in the identified hardening mechanisms to estimate the yield strengths (YS) of the different analyzed CuCrZr microstructures. The results are compared to the experimental values, including those of a reference wrought heat-treated CuCrZr, and discussed. A good correlation is found between calculated and experimental values. For the first time, the main hardening mechanisms of L-PBF CuCrZr are quantified and the interest of the “L-PBF + Direct Age Hardening (DAH)” process route to get a high amount of Cr nano-precipitates is confirmed. The DAH applied to L-PBF materials provides high mechanical properties (184 HV1 hardness, YS = 527 MPa, UTS = 585 MPa) while keeping a good elongation (14%) and electrical conductivity (42 MS.m−1). These results are due to a combination between (i) a high Cr nano-precipitates density, leading to a high precipitation hardening, and (ii) a high dislocation density associated to the presence of remaining solidification cells.

CuCrZr alloy produced by laser powder bed fusion: Microstructure, nanoscale strengthening mechanisms, electrical and mechanical properties

State-of-the-art of selective laser melting process: A comprehensive review

Manufacturing complex metal matrix composite (MMC) structures by laser powder-bed fusion (LPBF) could unleash their full potential but is difficult due to the presence of reinforcement. Unmelted particles negatively affect the pool dynamics, cause critical spatter ejections, and form printing defects. In this work, by taking copper (Cu) / diamond (D) composite as an example for its prospective thermal management applications and machinability limitations; we discovered that adding steps to LPBF enables the fabrication of high-quality materials and structures. We demonstrated that adding a recoating step improves the composite quality compared to structures manufactured by conventional LPBF. Adding a remelting step enabled further improvement by limiting the generation of spatter and printing defects, leading to 3D laser print dense (97%), highly thermally conductive (349 W/m K) and complex Cu/5 vol% D structures. Therefore, pursuing research into nonconventional LPBF could open new avenues for manufacturing MMCs.

Manufacturing of complex diamond-based composite structures via laser powder-bed fusion

Laser powder bed fusion (L-PBF) of copper alloys with high copper content is difficult due to the high infrared reflectivity and thermal conductivity of these alloys. In this study a simple and scalable method for coating copper powder with tin and nickel is presented, and suggested as an alloying strategy for such alloys. The coated powders were processed in a commercial L-PBF-machine at various scanning speeds. The samples made from coated powders show a lower amount of porosity compared to samples made from in-situ alloyed powders of similar composition.

Viktor Lindström

Papers

Laser Powder Bed Fusion of Metal Coated Copper Powders.

A Simple Scaling Model for Balling Defect Formation During Laser Powder Bed Fusion