Mechanically activated TiN nano-powders consolidated by spark plasma sintering and high-pressure methods

Titanium nitride (TiN) nano-powder was synthesized in a gas-pressure vessel steel via a mechanically induced reaction between Ti(α) and nitrogen gas for 40 h. Following mechanical activation, the precursor was consolidated using two distinct methods: spark plasma sintering (SPS) at 1600 °C for 10 min under an applied pressure of 50 MPa, and a high-pressure-high-temperature (HPHT) process performed at 1300 °C and 1600 °C under 7.8 GPa for 1 minute. The microstructure of the SPS-consolidated sample exhibited fine, uniform, pure TiN grains with an average size of 4.8 ± 2.0 μm. In contrast, the HPHT-consolidated material retains the TiN/TiN 0.3 milled grains nanostructure. Additionally, localized reactions between grains with varying nitrogen content lead to the formation of new TiN nanoparticles ranging in size from 23.1 ± 7.7 nm to 27.5 ± 10 nm, depending on the consolidation temperature. Variations in mechanical properties are attributed to the increased porosity and inhomogeneous microstructure in HPHT-synthesized samples, which impair load transfer and grain boundary bonding, thereby reducing compressive strength (1779 and 1624 MPa) and hardness (1441 ± 98 and 1538 ± 62 HV). The higher density, which is obtained through SPS consolidation with stoichiometric TiN ensures better strength (2416 MPa) and hardness (1796 ± 160 HV).