Fig. 1: Design principles and microstructures of nanocomposites by laser powder-bed-fusion (L-PBF).

a Schematic illustrating the manipulation of reinforcing particle structures via additive manufacturing (AM). An in situ nano-fragmentation process is utilized to spontaneously refine crystalline reinforcing microparticles into amorphous nanoparticles during L-PBF. This process involves the melting, nano-fragmentation, and rapid solidification of the reinforcing particles. GB denotes grain boundary. b Three-dimensional reconstructed scanning electron microscopy (SEM) images of the as-built composite. A cross-sectional electron backscatter diffraction (EBSD) image is superimposed to show the equiaxed grain structure. Melt pool boundaries (MPBs) and build direction (BD) are illustrated by the yellow dashed line and white arrow, respectively. c Aberration-corrected high-resolution transmission electron microscopy (HRTEM) image of a representative nanoparticle, with ultranano black regions distributed within the amorphous nanoparticles. At least twenty nanoparticles were characterized for microstructural identificaiton. d Enlarged view of the selected region in (c). The inset shows a fast Fourier transform (FFT) image of a region in the nanoparticle that does not contain Cu nanocrystals, suggesting an amorphous nature. e high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of a tiny nanocrystal along the [110] FCC zone axis and energy-dispersive X-ray spectroscopy (EDS) images of Cu, B and C atoms. f Three-dimensional atomic probe tomography (APT) reconstructions of Cu, B and C atom distributions in a typical APT tip including a matrix Cu–nanoparticle interface. The Cu, B and C atoms are coloured blue, yellow and red, respectively. g, h Measured distributions of the three atomic species near the interface and inside the nanoparticle, respectively. The phase boundary (PB) is indicated by the white line, and a representative tiny Cu cluster/nanocrystal is highlighted by a red circle. i Near-edge X-ray absorption fine-structure (NEXAFS) spectrum at the B–K edges of the extracted nanoparticles from the as-built composite.