Fig. 2: Nanofragmentation mechanism of microparticles.
From: Dispersion hardening using amorphous nanoparticles deployed via additive manufacturing
a Changes in the morphologies of reinforcing particles as a function of the input volumetric energy density, Ed. (Ed = P/vhd, where P is the laser power, v is the scan speed, h is the hatch distance, and d is the layer thickness). A representative HRTEM image of the interface and the corresponding FFT image of a region in the refined particle, displayed for samples processed with different Ed. The volume fraction of B4C is 12% in all samples. Images at different locations (at least five) show similar morphologies with the representative ones. Note that most of the refined particles (with an Ed value larger than 118.1 J/m3) have amorphous structures, thereby suggesting the melting–fragmentation–solidification process of B4C microparticles upon L-PBF. b–d High-fidelity multiphysics modelling of the change in the particle morphology during L-PBF. The coloured arrows represent the velocity vector in the melt, under which the initially microsized (~4 μm in diameter) particle is gradually fractured into nanoparticles. The particles are coloured based on their local temperatures. e Statistical calculation of the particle size distribution as a function of scanning time, as obtained from the simulation results. f SEM image of the as-built Al-B4C composites and HAADF-STEM image of interfacial structure of the selected region, showing the same in-situ nanofragmentation behaviour as in Cu, now forming ANPs with sizes ~200 nm. BD stands for build direction. Beam direction is along the [100] zone axis of aluminium. EDS mapping indicates that the composition of the nanoparticle is 78.7 ± 3.5 at% of B, 18.8 ± 3.6 at% of C and 2.5 ± 0.7% of Al, with little elemental diffusion or reaction at the interface. g The representative SEM image and HAADF-STEM image of as-built Cu-CrB2 composites. Micron-sized CrB2 with diameters of ~10 μm were used as the starting reinforcing particles, which have been spontaneously turned into amorphous nanoparticles with sizes of ~40 nm. Beam direction is along the [110] zone axis of copper. At least five different locations were independently observed for microstructures shown in (f and g) showing similar results.
