Synergistic reinforcement of carbon nanotubes and silicon carbide for toughening tantalum carbide based ultrahigh temperature ceramic

Tantalum carbide (TaC) is an ultrahigh temperature ceramic, where low damage tolerance limits its potential application in propulsion sector. In this respect, current work focuses on enhancing the toughness of TaC based composites via synergistic reinforcement of SiC and carbon nanotubes (CNTs). Spark plasma sintering of TaC, reinforced with 15 vol% SiC and 15 vol% CNT (processed at 1850 °C, 40 MPa, 5 min), has shown enhanced densification from ∼93% (for TaC) to ∼98%. Potential damage of the tubular CNTs to flaky graphite was revealed using transmission electron microscopy, and was supplemented via Raman spectroscopy. SiC addition has enhanced the hardness to ∼19.5 GPa while a decreases to 12.6 GPa was observed with CNT addition when compared to the hardness of TaC (∼15.5 GPa). The increase in the indentation fracture toughness (from 3.1 MPa m1/2for TaC to 11.4 MPa m1/2) and fracture strength (from ∼23 MPa for TaC to ∼183 MPa) via synergetic reinforcement of SiC and CNT is mainly attributed to energy dissipating mechanisms such as crack branching, CNT bridging, and crack-deflection. In addition, the reduction of interfacial residual tensile-stresses with SiC- and CNT-reinforcement, resulting an overall increase in the fracture energy and toughening, is also established.