Fabrication of carbon nanofiber(CNF)-dispersed Al2O3 composites by pulsed electric-current pressure sintering and their mechanical and electrical properties

Dense Al2O3-based composites (≥99.0% of theoretical) dispersed with carbon nanofibers (CNFs) were fabricated using the pulsed electric-current pressure sintering (PECPS) for 5 min at 1300°C and 30 MPa in a vacuum. The dispersion of CNFs into the matrix depended much on the particle size of the starting Al2O3 powders. Mechanical properties of the composites were evaluated in relation with their microstructures; high values of three-point bending strength σb (∼800 MPa) and fracture toughness K IC (∼5 MPa·m1/2) were attained at the composition of CNF/Al2O3 = 5:95 vol%, which σb and K IC values were ∼25% and ∼5%, respectively, higher than those of monolithic Al2O3. This might be due to the small Al2O3 grains (1.6 μm) of dense sintered compacts compared with that (4.4 μm) for the pure Al2O3 ceramics, resulting from the suppression of grain growth during sintering induced by uniformly dispersed CNFs in the matrix. Electrical resistivity of CNF/Al2O3 composites decreased rapidly from >1015 to ∼2.1 × 10−2 Ωm (5vol%CNF addition), suggesting the machinability of Al2O3-based composites by electrical discharge machining.