Unprecedented simultaneous enhancement in strain tolerance, toughness and strength of Al2O3 ceramic by multiwall-type failure of a high loading of carbon nanotubes.

Carbon nanotubes (CNTs) have a remarkable load-bearing ability. Recently, however, multi-walled CNTs (MWCNTs) have been shown to possess dramatically higher load-bearing ability when intimately embedded in an oxide ceramic (Al2O3), because the load could be transferred not to only their outermost walls but also their generally unloaded inner walls via the strong interwall shear resistance originating from residual compressive stresses. This phenomenon is characterized by an uncommon, highly energy-dissipating, multiwall-type failure of individual MWCNTs during hybrid fracture, with no evidence of pullout. Here, we demonstrate that this nanoscale in-MWCNT load-transfer process, at an optimized, high loading of MWCNTs (10 vol%) and in a pore-free and uniform platform, leads to unprecedented, dramatic simultaneous enhancement in strain tolerance (81%), fracture toughness (52.2%), and flexural strength (22%) of the Al2O3 ceramic matrix. The extent of toughening by this mechanism is also the highest ever reported. This unprecedented performance by using a high loading of functional MWCNTs, namely, toughening, strengthening, softening and lightening, simultaneously and at this level, has implications for many functional and structural applications.