Nanoparticle dispersion effect of laser-surface melting in ZrB_2p/6061Al composites

Zirconium diboride (ZrB_2p, 15 vol%)/6061 aluminum (Al) composites were fabricated via in situ reaction. The existence, morphologies, and dispersion degree of the in situ ZrB₂ particles with size from tens to hundreds of nanometers were studied by X-ray diffractometry, energy-dispersive X-ray spectroscopy, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy. As the particle-settlement effect becomes dominant during the composite fabrication process, ZrB₂ nanoparticles agglomerate to a certain extent in some areas of the as-cast composites. A laser-surface melting (LSM) strategy was applied to disperse agglomerated ZrB₂ nanoparticles in as-cast composites, and the ZrB₂ nanoparticle dispersion is affected visibly by LSM. After LSM, nanoparticles tend to distribute along the grain boundary. Particle clusters were dispersed in an explosive orientation and the particle diffusion distance varied in terms of its radius and melt-viscosity vicinity. High-resolution transmission electron microscopy showed the existence of a subgrain structure near the ZrB₂–Al interface after LSM. This may increase the yield strength when a dislocation tangle forms.