Effect of carbon nanotube on processing, microstructural, mechanical and ablation behavior of ZrB2-20SiC based ultra-high temperature ceramic composites

Herein, zirconium diboride (ZrB2) is reinforced with silicon carbide (SiC) and carbon nanotube (CNT) to provide enhanced structural stability and oxidation protection against extreme thermal (>2400 °C) and oxidative environments. The ablation resistance of ZrB2-based composites was evaluated using plasma arc-jet with a heat-flux of 2.5 MW/m2 for 30 s, and the decreased oxidation-rate (from 0.77 μm/s to 0.44 μm/s) is attributed to enhanced thermal conductivity (42.3-52.3 W/mK at 1200 °C) with synergistic reinforcement of SiC and CNT. The increased onset temperature (from 679 °C to 706 °C) and decreased enthalpy of oxide formation (from 1.6 to 0.6 kJ/g), insinuates an increase in thermal stability and oxidation resistance with the synergistic addition of both SiC and CNT in ZrB2. The increase in the hardness of ZrB2 in the as-processed composites (up to 1.6 times) as well as after plasma arc jet exposure (up to 2.1 times) with synergistic reinforcement of SiC and CNT has shown to suppress crack-formation and restrict oxidation. The reduction in the analytically evaluated tensile interfacial residual stress indicates enhanced structural integrity of ZrB2-SiC-CNT composites, which is a mandatory requirement for aerospace applications.

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