Morphological analysis and high-temperature phase stability of spark plasma sintered TiN-MWCNTs ceramic composite

The microstructure, mechanical properties, and phase stability of TiN+MWCNTs ceramic-based composite were studied. Ball milling and spark plasma sintering (SPS) techniques were adopted for synthesizing titanium nitride (TiN) composites containing 1, 3, and 5 wt. percent (wt. %) multiwalled carbon nanotubes (MWCNT). At a temperature of 1000 °C where the phase stability was investigated, the effects of MWCNT addition on thermal treatment and mechanical characteristics of the fabricated composites were explored. According to the results, the resultant effect of ball milling on the ad-milled powders and sintering at a temperature of 1800 °C played a critical role in the homogenous diffusion of MWCNTs into the TiN ceramic matrix. It was further noted that the addition of different wt. % of multiwalled carbon nanotube helped in stabilizing the FCC-crystal phases at this elevated temperature. A slight transformation was observed in the microstructures, as the core and the outer rim phases remained stable in their crystallographic orientation. The varying addition of MWCNTs retained the α-FCC phase both at the core and the outer rim phase during and after thermal exposure of 1000 °C for 3 h. The composite with 1wt. % MWCNT content exhibited the highest hardness of 40 GPa with a fracture toughness of 12.22 MPa m^1/2, while the least hardness value of 12.5 GPa was recorded by the unreinforced TiN sample. The effect of mechanical alloying and thermal exposure of the ceramic composites significantly enhanced the strengthening and toughening of the composites.