TiN–TiB2 composites prepared by various sintering techniques

• Composites prepared using the pressureless sintering were found to have by good physical and mechanical properties.
• Lattice constants of the TiN obtained by free and SPS sintering were larger than for the standard stoichiometric TiN.
• Materials prepared using the pressureless sintering are characterized by the highest fracture toughness.

TiN–TiB2 composites were prepared by pressureless, Spark Plasma Sintering (SPS) and high pressure–high temperature (HP–HT) sintering techniques. Powder mixtures, in wt.%, 70 TiN–30 TiB2 and 50 TiN–50 TiB2, were based on commercial TiN and TiB2 micropowders. Parameters of sintering processes were optimized for density, hardness and Young's modulus. Young's moduli were in the range 422–460 GPa for the 70–30 composite and for the 50–50 composite they were in the range 416–482 GPa. Vickers hardnesses were ~ 15 GPa for the 70–30 composite and in the range 16.4–17.5 GPa for the 50–50. Relative density ranged from 95.7% (HP–HT, 50–50 composite) to 99.0% (SPS, 70–30 composite). HP–HT composites had lower densities and Young's moduli, because of microcrack's. Nitrogen contents, lattice constants and analyzed microstructures depended on the method of sintering. The smallest grain growth, of TiN particles, from 1.2 μm to 2.5 μm, without the size changing for the TiB2 particles, was observed for the HP–HT TiN–TiB2 composite, when there was crushing of TiB2 particles. In pressureless sintered composites the growth of TiN grains was from about 1.2 μm to 4.9 μm. Materials prepared using the pressureless sintering method were characterized by the highest fracture toughness: 6.38 and 6.89 MPa·m1/2 for the 70 TiN–30 TiB2 and 50 TiN–50 TiB2 composites, respectively. The pressureless sintered TiN–TiB2 composites had the best combination of physical and mechanical properties.