Synthesis route and mechanical properties of reactive hot pressed TiN–TiB2 ceramics

Reaction process and phase formation mechanisms in reactive hot pressing (RHP) of titanium and boron nitride blend powders have been investigated in vacuum. In temperatures of up to 1300 °C, chemical reactions in the Ti–BN blend powder proceed via a solid-state diffusion process. Intermediate phases of hexagonal α-TiN0.3, tetragonal Ti2N, nonstoichiometric cubic TiN0.9 and orthorhombic TiB are found before they finally transform to the stoichiometric cubic TiN and hexagonal TiB2. Both the TiN–TiB2 ceramics reactive hot-pressed at 1600 and 1800 °C represent intragranular/intergranular distributions of TiB2 in TiN. In contrast with monolithic TiN and TiB2 ceramics, the reactive hot-pressed TiN–TiB2 exhibits a significant enhancement on flexural strength and fracture toughness. TiN–TiB2 ceramics reactive hot-pressed at 1800 °C have a Vickers hardness of 17.8 GPa, an elastic modulus of 475 GPa, a flexural strength of 732 MPa and a fracture toughness of 8.5 MPa·m1/2.

► Intermediate phases of α-TiN0.3, Ti2N, TiNx and TiB are found in TiN–TiB2 ceramics.
► TiN–TiB2 ceramics show intra-granular/inter-granular distributions of TiB2 in TiN.
► TiN–TiB2 ceramics reactive hot-pressed at 1800 °C have a high flexural strength of 732 MPa.
► TiN–TiB2 ceramics reactive hot-pressed at 1800 °C have a high fracture toughness of 8.5 MPa·m1/2.