Laser powder bed fusion (LPBF) of pre-alloyed nanocomposite powders, such as AlSi10Mg reinforced with TiB2 nanoparticles, represents a significant advancement in additive manufacturing (AM) of high-performance metal matrix composites. The process involves selectively melting layers of powder using a high-energy laser to fabricate complex geometries with tailored properties. However, achieving uniform nanoparticle dispersion and preventing agglomeration during melting remains a critical challenge. Process parameter optimization is essential to control melt pool dynamics, thermal gradients, and solidification behavior, ultimately influencing the microstructure and mechanical properties of the final component.

The LPBF process for nanocomposites requires precise control over laser power, scan speed, hatch spacing, and layer thickness to ensure complete melting of the matrix while avoiding excessive energy input that could lead to nanoparticle agglomeration or evaporation. For AlSi10Mg/TiB2 systems, typical laser power ranges between 150-400 W, with scan speeds of 500-2000 mm/s, depending on the desired melt pool dimensions. Excessive energy density can cause TiB2 nanoparticles to cluster due to localized overheating, while insufficient energy may result in poor bonding between layers. Optimal volumetric energy density, typically between 50-150 J/mm³, must be maintained to balance these competing factors.

Rapid solidification inherent to LPBF results in unique microstructural features, including fine-grained matrices and non-equilibrium phases. In AlSi10Mg/TiB2 nanocomposites, cooling rates exceeding 10^5 K/s promote the formation of ultrafine cellular structures with grain sizes often below 1 µm. The TiB2 nanoparticles act as nucleation sites, further refining the microstructure and enhancing mechanical properties. However, the directional heat transfer during LPBF leads to anisotropic microstructures, with elongated grains along the build direction. This anisotropy manifests in mechanical properties, where vertical specimens may exhibit 10-20% lower ductility compared to horizontal specimens due to preferential grain orientation.

Preventing nanoparticle agglomeration requires careful powder preparation and process control. Gas atomized pre-alloyed powders with TiB2 content between 1-5 wt.% are commonly used, with particle sizes ranging from 15-45 µm for optimal flowability. The nanoparticles should be uniformly distributed in the powder feedstock, achieved through advanced milling or coating techniques. During LPBF, Marangoni convection within the melt pool can help distribute nanoparticles, but excessive fluid flow may also promote clustering. Process parameters must be tuned to maintain sufficient melt pool turbulence for dispersion while avoiding excessive agitation that could lead to segregation.

The resulting nanocomposites exhibit significantly improved mechanical properties compared to unreinforced alloys. AlSi10Mg with 3 wt.% TiB2 typically shows a 30-50% increase in yield strength (300-400 MPa) and hardness (120-150 HV), while maintaining adequate ductility (5-8%). The strengthening mechanisms include Orowan strengthening from nanoparticle dispersion, grain boundary strengthening from refined microstructures, and load transfer from the reinforcement phase. The high cooling rates also lead to supersaturated solid solutions and fine eutectic silicon networks, contributing to additional strengthening.

LPBF enables the fabrication of functionally graded nanocomposite components with spatially tailored properties. By varying process parameters or powder composition layer-by-layer, components can be engineered with gradual transitions in hardness, wear resistance, or thermal conductivity. For example, a gear component might feature higher TiB2 concentration at the tooth surface for wear resistance, gradually decreasing toward the core for improved toughness. This design freedom is particularly valuable for aerospace and automotive applications where weight reduction and performance optimization are critical.

Post-processing heat treatments can further modify the microstructure and properties of LPBF nanocomposites. Stress relief annealing at 300°C for 2 hours reduces residual stresses while preserving the nanostructured features. Higher temperature treatments (500°C) can precipitate secondary phases and improve ductility, though with some sacrifice in strength. The thermal stability of TiB2 nanoparticles allows retention of reinforcement benefits even after high-temperature exposure, unlike some metastable microstructural features formed during rapid solidification.

Quality control remains a challenge for LPBF nanocomposites, requiring advanced characterization techniques. X-ray computed tomography can detect nanoparticle clusters or porosity, while electron backscatter diffraction reveals microstructural anisotropy. In-process monitoring using pyrometers or high-speed cameras helps identify defects related to improper melting or nanoparticle distribution.

The combination of LPBF and nanocomposite materials opens new possibilities for lightweight, high-strength components with complex geometries unattainable through conventional manufacturing. Ongoing research focuses on expanding the range of compatible matrix-reinforcement systems, improving process reliability, and developing predictive models for microstructure-property relationships. As the technology matures, standardized parameter sets and quality assurance methods will facilitate broader industrial adoption of additively manufactured metal matrix nanocomposites.