Extraordinary reinforcing effect of carbon nanotubes in aluminium matrix composites assisted by in-situ alumina nanoparticles

Existing aluminium metal matrix composites (Al MMCs) can attain both high tensile yield strength (>500 MPa) and high elastic modulus (>90 GPa) but usually at the expense of tensile strain-to-fracture (~5% or less). Here we report the development of a novel class of Al MMCs that can offer tensile yield strength of 515 ± 17 MPa, elastic modulus of 95.6 ± 1.7 GPa and tensile strain-to-fracture of 10.4 ± 0.8%. Our design hypothesis is to reinforce the Al matrix with ex situ introduced carbon nanotubes (CNTs) for primary strengthening but at the same time we craft a high number density of in situ formed ultrafine γ-Al₂O₃ nanoparticles to improve dimple fracture. Together they act in concert to render outstanding tensile properties. The strengthening and failure mechanisms of the as-fabricated Al-CNTs-γ-Al₂O₃ MMCs are characterized in detail. The design concept proposed and validated in this study can be informative for the fabrication of other high-performance carbon-reinforced MMCs.