Microparticle-Assisted Copper LPBF with Dual-Scale LaB6 Strengthening

Copper is an important engineering material because it combines efficient electrical and thermal transport with useful structural integrity. Its high electrical and thermal conductivity make it suitable for components that carry current, remove heat, or operate in thermally demanding assemblies. At the same time, many such components increasingly require geometries that are difficult to produce by conventional subtractive or forming methods. Laser powder bed fusion offers an attractive manufacturing approach in this setting because it can build dense metal parts directly from powder while allowing considerable geometric freedom. The main challenge comes from the interaction between copper and the near-infrared lasers commonly used in commercial LPBF systems. Copper reflects much of the incident radiation at these wavelengths, so only a limited fraction of the applied energy is absorbed by the powder bed. Also the high thermal conductivity of copper can bring another challenge because heat spreads rapidly away from the irradiated region, which make it harder to maintain a stable melt pool and reliable fusion between adjacent scan tracks and layers. The result is a narrow processing range in which relatively small changes in laser power or scan speed can shift the material toward lack-of-fusion defects, porosity, spheroidization, or unstable keyhole behaviour.

Several approaches have been explored to improve the LPBF processing of copper. Higher-power near-infrared lasers can increase energy delivery, while shorter-wavelength laser sources can improve absorption. These solutions, however, may require costly equipment or introduce practical limitations related to system capability and laser–material interaction. A different route is to modify the powder itself. Alloying additions can improve printability, but elements that dissolve substantially in copper may also impair electrical conductivity through electron scattering. For applications in which copper is selected primarily for its transport properties, this trade-off is difficult to ignore.

Particle-based modification provides another possibility. A dispersed additive can alter the optical and thermal response of the powder bed while remaining distinct from the copper matrix to a meaningful extent. LaB₆ is of particular interest because of its high absorptivity under near-infrared irradiation and its potential to remain as a second phase in copper. Earlier studies have considered nanoscale LaB₆ additions, but nanoparticles are prone to agglomeration and may reduce powder flowability, complicating powder spreading during LPBF. Their preparation can also be costly.

Micrometre-scale LaB₆ particles offer a potentially more practical alternative, yet their behaviour during copper LPBF has remained insufficiently understood. Whether such particles can improve laser absorption and densification while also influencing microstructural development, mechanical response, and electrical or thermal transport requires direct examination. The present investigation addresses that question by introducing LaB₆ microparticles into copper powder and examining how they affect the printing process and the resulting material.

In a recently published research paper in Journal of Manufacturing Processes Dr. Jinchao Zhao, Professor  Jiabin Liu, Dr.  Liuyi Huang, Professor  Kai Ren, and Professor Yanlong Cao from Zhejiang University developed a 1 wt% LaB₆ microparticle-modified copper feedstock for near-infrared laser powder bed fusion. The powder preparation combined ultrasonic vibration mixing with three-dimensional mixing to distribute LaB₆ across copper particles. During printing, the material produced a dual-scale LaB₆ structure composed of retained larger particles and in situ precipitated nanoscale LaB₆ particles. This combination increased near-infrared absorptivity, broadened the high-density processing window, and strengthened the printed copper without eliminating its high electrical and thermal conductivity.

The researchers prepared the composite feedstock by combining gas-atomized copper powder with irregular LaB₆ microparticles using ultrasonic vibration mixing followed by three-dimensional mixing under argon protection. Elemental mapping showed that the LaB6 particles were distributed across the copper-powder surfaces rather than concentrated in isolated regions. This dispersion was important because the intended effect depended on LaB6 being available throughout the powder bed to interact with incident laser energy. They found that at 1080 nm, adding LaB₆ microparticles increased powder absorbance by 50.4%, changing the densification behaviour during LPBF. Across a substantially broader range of processing conditions than pure copper, the composite achieved relative densities above 99.9%, whereas unmodified copper remained more susceptible to unfused regions and porosity when laser input was insufficient.

The benefit was therefore not confined to a single optimized condition. The authors found that the high-density processing window of the composite was approximately twice as wide as that of pure copper, which indicates greater tolerance to parameter variation during printing. The composite also developed larger melt-pool widths and depths under comparable conditions. By improving laser-energy coupling within the powder bed, LaB6 promoted more stable melting and supported fusion between neighbouring tracks and successive layers.

The team performed microstructural analysis which showed that the initial microparticle population did not behave uniformly during LPBF. Larger LaB₆ particles remained partially or fully unmelted in some regions and were redistributed within the liquid copper by melt-pool flow before becoming embedded on solidification. Their number decreased as volumetric energy density increased, consistent with greater particle melting at higher energy input. At the same time, transmission electron microscopy identified a second LaB6 population: regularly shaped nanoparticles with an average size of approximately 60 nm dispersed in the copper matrix.

This nanoscale population was interpreted as the result of complete melting of smaller LaB₆ particles, dissolution into the liquid copper, and subsequent precipitation during rapid solidification. La and B became supersaturated in the melt and reprecipitated as LaB₆ nanoparticles within grains and at grain boundaries. They found using X-ray diffraction no measurable shift in copper lattice parameters or the formation of new phases, supporting the interpretation that LaB6 remained a second phase rather than producing a substantially altered copper solid solution. The team found that both pure copper and composite samples retained a columnar grain structure aligned with the build direction and the composite showed weaker texture, a higher fraction of low-angle grain boundaries, and greater kernel average misorientation, consistent with increased lattice distortion and dislocation density. These changes were reflected in the tensile response: the LaB₆/Cu composite reached a yield strength of 260 MPa and an ultimate tensile strength of 385 MPa, compared with 127 MPa and 246.5 MPa for LPBF pure copper. Its elongation decreased from 34% to 25.6%, although the composite remained appreciably ductile.

Overall, the findings of Zhejiang University researchers are relevant to copper components that must retain high electrical and thermal transport while being manufactured in geometries that are difficult to obtain through conventional routes. The composite retained 87.4% IACS electrical conductivity and a calculated thermal conductivity of 359 W·m⁻¹·K⁻¹ while providing substantially higher strength than the LPBF pure-copper material.  Electrical components with complex internal or external geometries are one clear area of relevance. Copper is widely used where current must be carried efficiently, but the present results indicate that a modest LaB₆ addition can preserve much of that electrical capability while improving the mechanical response of LPBF-built material.

Thermal-management hardware is another direct application area identified by the paper’s starting context. The retained thermal conductivity supports the use of the material where heat must be transferred through a printed copper body, while LPBF provides access to geometrically intricate forms. Such flexibility matters for designs that depend on internal passages, local thickness variations, integrated mounting features, or compact heat-transfer pathways that would be difficult to machine from bulk copper. The present study does not demonstrate a specific thermal-management device, but it establishes a materials-processing route compatible with that class of component.

The manufacturing implications are equally important and by introducing 1 wt% LaB₆ increased powder absorptivity by 50.4% and expanded the high-density parameter range by more than 1.8 times relative to pure copper. This broader process window gives engineers greater latitude when selecting laser power and scan speed, and it can reduce the sensitivity of production to small parameter variations.

Microparticle-based feedstock modification may also be attractive where powder preparation must remain practical. The paper emphasizes that micrometre-scale particles distribute more readily than nanoparticles and can reduce preparation complexity and cost. Their behaviour during printing is especially useful: larger LaB₆ particles can remain dispersed in the copper matrix, whereas smaller particles melt and reprecipitate as nanoscale LaB₆ during solidification. The resulting dual-scale structure links processability with strengthening, while retaining the conductive character required for electrically and thermally functional copper parts.