Reaction Sintering of Machinable TiB₂-BN-C Ceramics with In-Situ Formed h-BN Nanostructure

Soft TiB₂-BN-C hetero-modulus ceramics were sintered with the assistance of in-situ reactions during the hot pressing of TiN-B₄C precursors. TiB₂ 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 B₄C to TiN. Reactive sintering route allows almost full densification of TiB₂-BN-C composite ceramics at 1900 °C. The processes enable the formation of multilayer h-BN nanosheets inside the TiB₂ matrix. The manufactured TiB₂-33BN-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.