Effect of SiC content on electrical, thermal and ablative properties of pressureless sintered ZrB2-based ultrahigh temperature ceramic composites

The effects of SiC content (10-40 vol.%) on electrical, thermal and ablation properties of pressureless sintered ZrB2-SiC composites showing interfacial segregation of W-rich phases have been studied. The electrical resistivity was measured by four-probe method, whereas thermal diffusivity and coefficient of thermal expansion (CTE) were determined using laser-flash method and thermo-mechanical analyzer, respectively. Whereas thermal conductivities calculated from experimentally obtained thermal diffusivity values are found to be the highest for the ZrB2-20 SiC composite, both electrical conductivity and CTE decrease with increasing SiC content. The specimens were subjected to thermal shock by soaking at 800-1200 degrees C, followed by water-quenching. Further, some specimens were exposed to oxyacetylene flame (2200 degrees C) for 10 min. The damage was estimated from changes in mass, Young's modulus, and hardness. The highest thermal shock and ablation resistance have been observed for the ZrB2-20 SiC composite, as thermal properties and formation of protective oxide scale play key role. (C) 2016 Elsevier Ltd. All rights reserved