Macro-micro-nano multistage toughening in nano-laminated graphene ceramic composites

Ceramics can be toughened by traditional toughening methods including particle-dispersion, phase-transformation and whisker toughening, but such strategies usually impact the hardness or strength adversely. Inspired by the structural guidelines originated from the study of bamboo and nacre, herein, we developed exceptionally tough and hard quaternary nanocomposites through constructing hierarchical structures spanning several scales within the ceramic matrix employing bottom-up assembly approach. New-concept advanced macro-micro-nano multistage toughening mechanism was proposed and identified, of which laminated structure toughening, two-dimensional (2D) multilayer graphene toughening and multi-component zero-dimensional (0D) nanoparticles toughening were defined as the 1st-stage, 2nd-stage and 3rd-stage toughening mechanism, respectively. An extraordinary fracture toughness of 14.9 MPa m^1/2, nearly three-fold that of monolithic ceramic with the comparable hardness (25.6 GPa), was achieved. This nanocomposites also exhibited dramatically higher toughening efficiency in comparison with that in other reported ceramic matrix including graphene and carbon nanotube toughened nanocomposites. This successful low-cost toughening mechanism constitutes a step forward in developing high-tough and high-hard advanced ceramic matrix composites to be applied for state-of-art engineering structural as well as functional applications including biomedical implants, aero-engine component, electrical capacitors, transportation systems and energy storage.