Strengthening and toughening of aluminum by single-walled carbon nanotubes

Effects of single-walled carbon nanotubes (SWNTs) on strengthening and toughening behaviors of aluminum-based composites with grain sizes ranging from nano- to micrometer have been investigated. The strength of composites is enhanced as an increase in SWNT volume and a decrease in grain size. Nanocrystalline composite containing 3.5 vol.% SWNTs exhibits good ductility of ∼5% tensile elongation to failure as well as superior yield stress of ∼600 MPa. However, the strengthening efficiency of SWNTs becomes half of the theoretical prediction for nanocrystalline composites due to the recovery process around the interface. Nanocrystalline composite containing 2.0 vol.% SWNTs shows the fracture toughness of ∼57 MPa mm1/2, which is five times higher than that of starting aluminum. SWNTs may effectively block the propagation of necks and cracks, providing much improved ductility and toughness.