Nanoceramic composites with duplex microstructure break the strength-toughness tradeoff

There is a strength and fracture toughness tradeoff in nanoceramic composite. The strength varies reciprocally with the grain size whereas the toughness contributed by compressive residual stress increases with the dimension of the second phase. In this work, a novel duplex microstructure with reinforced clusters composing of nanosized grains was proposed and validated using a model system of B 4 C-TiB2 ceramics densified by carbide boronizing. As-obtained ceramics exhibit excellent combined mechanical properties at room temperature, including Vickers hardness, Young's modulus, flexural strength and fracture toughness (by surface crack in flexure method) of 32.1 +/- 2.7 GPa, 506.9 +/- 2.0 GPa,1175 +/- 71 MPa and 5.1 +/- 0.4 MPa m(0.5), respectively. Both strength and toughness are at least similar to 30 % higher than the counterparts with similar composition but homogenously distributed TiB2 grains. Graphite onion was confirmed to be an intermediate product during reactive sintering, it facilitated the grain pullout during fracture and retained the nanometric TiB2 grain in the cluster, both of which also contribute the toughening and strengthening mechanisms in the B4C-TiB2 ceramics. (C) 2020 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.