Driven by the rapid development of additive manufacturing technologies and the trend towards mass customization, the development of new feedstock materials has become a key aspect. Additivation of the feedstock with nanoparticles is a possible route for tailoring the feedstock material to the printing process and to modify the properties of the printed parts. This study demonstrates the colloidal additivation of PA12 powder with laser-synthesized carbon nanoparticles at >95% yield, focusing on the dispersion of the nanoparticles on the polymer microparticle surface at nanoparticle loadings below 0.05 vol%. In addition to the descriptors “wt%” and “vol%”, the descriptor “surf%” is discussed for characterizing the quantity and quality of nanoparticle loading based on scanning electron microscopy. The functionalized powders are further characterized by confocal dark field scattering, differential scanning calorimetry, powder rheology measurements (avalanche angle and Hausner ratio), and regarding their processability in laser powder bed fusion (PBF-LB). We find that heterogeneous nucleation is induced even at a nanoparticle loading of just 0.005 vol%. Finally, analysis of the effect of low nanoparticle loadings on the final parts’ microstructure by polarization microscopy shows a nanoparticle loading-dependent change of the dimensions of the lamellar microstructures within the printed part.

We investigate dynamics of a single cavitation bubble in vicinity to a horizontal wall throughout expansion and collapse using a sharp-interface level-set method. The numerical scheme is based on a finite-volume formulation with low-dissipation high-order reconstruction schemes. Viscosity and surface tension are taken into account. The simulations are conducted in three-dimensional axi-symmetric space. A wide range of initial bubble wall standoff distances is covered. We focus, however, on the near-wall region where the distance between the bubble and the wall is small. We reproduce three jetting regimes: needle, mixed, and regular jets. The needle jets impose a significant load on the solid wall, exceeding the force induced by the collapse of the pierced torus bubble. For intermediate standoff distances the large delay time between jet impact and torus bubble collapse leads to a significant decrease of the imposed maximum wall-pressure. A liquid film between bubble and wall is observed whenever the bubble is initially detached from the wall. Its thickness increases linearly for very small standoff distances and growths exponentially for intermediate distances leading to a significant increase of wall-normal bubble expansion and bubble asymmetry. For configurations where the torus bubble after jet impact reaches maximum size, the collapse time of the cavitation bubble also is maximal, leading to a plateau in the overall prolongation of the cycle time of the bubble. Once the initial bubble is attached to the solid wall, a significant drop of all macroscopic time and length scales towards a hemispherical evolution is observed.

Applications of nanoparticles in medicine, energy, catalysis, or additive manufacturing demand the development of nanoparticle production methods that are offering material and solvent versatility, high purity, morphology, and size control, together with industrial-scale production capabilities. Pulsed laser ablation in liquids is a technique that comes close to meeting these demands; however, nanoparticle size control remains a challenge. To reduce the characteristic bimodality in nanoparticles synthesized by high-intensity pulsed laser ablation in liquids, a double pulse configuration with inter-pulse delays between 300 ps and 1200 ps is proposed. In this temporal delay window, the plume and initial bubble are still flat so that shielding of the second laser pulse by the cavitation bubble is avoided; minimizing pulse shielding that could reduce nanoparticle productivity. At a pulse delay of 600 ps, a (9  ± 1) wt% reduction of the large nanoparticle fraction is demonstrated (at the expense of mass yield), showing the possibility of modifying the nanoparticle size distribution produced in pulsed laser ablation in liquids by temporal pulse shaping.