Evaluation of mechanical properties and microstructures of multi-walled carbon Nanotube/Alumina composites prepared by pressureless sintering

Alumina ceramics reinforced with multi-walled carbon nanotubes (MWCNTs) have been prepared by pressureless sintering. Resultant composites with the MWCNT contents up to 0.9 vol.% have shown relative density as high as 98%. In addition, with increasing the MWCNT contents up to 0.9 vol.%, bending strength and fracture toughness of the composites is found to be increase gradually, and the composite containing 0.9 vol.% MWCNTs have shown 18% and 32% simultaneous increases in bending strength (699.1 ± 46.1 MPa) and fracture toughness (5.33 ± 0.03 MPa·m1/2), respectively, compared with MWCNT-free alumina. Observations on the fracture surface and the tensile-loading experiments of MWCNTs using an in-situ SEM method with a nanomanipulator system demonstrate that the MWCNTs, rather than pulling out from the alumina matrix, tend to fail in so-called "clean break" manner. Theoretical calculations imply that tougher ceramics with MWCNT can be obtained by creating the appropriate interaction between the matrix and MWCNT: not too week but also not too strong to permit an adequate load transfer between the two parts and thus a consequent pulling out without breakage of MWCNT. For the design of tougher ceramics with MWCNTs, appropriate modification of fiber/matrix interface will be one of important factors.