Spark plasma sintered tantalum carbide–carbon nanotube composite: Effect of pressure, carbon nanotube length and dispersion technique on microstructure and mechanical properties

▶ Spark plasma sintering was used to synthesize 100% dense TaC–CNT composites. ▶ Addition of CNTs aided densification and inhibited grain coarsening. ▶ HRTEM elucidated the effect of very high pressures and temperature on CNTs. ▶ Improvement in the fracture toughness was observed by CNT addition. ▶ A comparison of effect of long and short CNTs on various aspects has been studied. TaC–4wt.% CNT composites were synthesized using spark plasma sintering. Two kinds of CNTs, having long (10–20μm) and short (1–3μm) length, were dispersed by wet chemistry and spray drying techniques respectively. Spark plasma sintering was carried out at 1850°C at pressures of 100, 255 and 363MPa. Addition of CNTs leads to an increase in the density of 100MPa sample from 89% to 95%. Short CNTs are more effective in increasing the density of the composites whereas long CNTs are more effective grain growth inhibitors. The longer CNTs are more effective in increasing the fracture toughness and an increase up to 60% was observed for 363MPa sample. Hardness and elastic modulus are found to increase by 22% and 18% respectively for 100MPa samples by addition of long CNTs. Raman spectroscopy, SEM and TEM images indicated that the CNTs were getting transformed into flaky graphitic structures at pressure higher than 100MPa.