The role of graphite addition on spark plasma sintered titanium nitride

Composites of titanium nitride reinforced with graphite were synthesized using spark plasma sintering at 2000 °C. The effects of graphite addition on the microstructure, relative density, and mechanical properties of TiN ceramics matrix were examined. The investigation was performed on TiN powder with varying graphite content (1–5 wt.%) for 8 h using an energy ball milling equipment. Results show that TiN without and with graphite (TiN + 1 wt.% graphite) sintered at 2000 °C recorded sintered relative density of 96.7% and 97% respectively. Additionally, TiN with 3 wt.% graphite had a relative density of 98%. However, the shrinkage of TiN + 3 wt.% graphite was observed to be the lowest compared to other composites at the same sintering conditions. Microstructural analysis indicates that the grain of titanium nitride in the composite was very fine and continuous. Subsequently, a bimodal particle sizes were observed when 5 wt.% graphite was dispersed in TiN. The highest Vickers microhardness of 23.5 GPa and fracture toughness of 6.5 MPa m1/2 were achieved with composites reinforced with 3 wt.% graphite at milling period of 8 h. The combination of TEM/EDS and HRTEM/FFT show a single pattern of diffraction and consistency in interplanar distance obtained from X-ray diffractometry of the milled sample. There is a clear coherence interface between the phases.