Reaction Sintering of Machinable TiB 2 -BN-C Ceramics with In-Situ Formed h-BN Nanostructure.

Soft TiB 2 -BN-C hetero-modulus ceramics were sintered with the assistance of in-situ reactions during the hot pressing of TiN-B 4 C precursors. TiB 2 formation was observed already after the hot pressing at 1100 °C, remaining the only phase identifiable by XRD even after sintering at 1500 °C. Analysis of reaction kinetics allows us to assume that the most probable reaction controlling stage is boron atoms sublimation and gas phase transfer from B 4 C to TiN. Reactive sintering route allows almost full densification of TiB 2 -BN-C composite ceramics at 1900 °C. The processes enable the formation of multilayer h-BN nanosheets inside the TiB 2 matrix. The manufactured TiB 2 -33BN-13C ceramic with K 1C = 5.3 MPa·m 1/2 and H V = 1.6 GPa is extremely thermal shock-resistant at least up to quenching temperature differential of 800 °C. The sintered UHTC composite can be machined into complex geometry components.