Cyclic Ablation Behaviors of ZrB2-SiC Composites Sintered with Nano-Sized Particles

Ultra-high temperature ceramic (UHTC) is one of the most promising materials used in thermal protection system for hypersonic flight vehicles. In this work, ZrB2-0.5 vol% SiC composites are fabricated with nano-sized ZrB2 and SiC particles by spark plasma sintering (SPS) at 1500 degrees C. The average density of the composites reaches 5.47 g cm(-3), while the average grain size is only 1 mu m. Then, single and cyclic ablation tests are conducted using a plasma generator. Ablation mechanisms and microstructure evaluation of the composites are discussed in detail. In addition, a digital optical microscope system is adopted to obtain the surface micrograph after ablation. Results show that ablation center will become protuberant rather than form an ablation crater, due to the relative porous and loose oxide layer and flushing action of ablation flame. Thickness of oxide layer and mass gain of the sample obviously increase during the single ablation, while the mass change rate decreases gradually and is then kept stable with the ablation time increasing. Compared with the single ablation, the cyclic ablation leads to higher mass gain and mass change rate, as many microcracks formed on the surface which will significantly accelerate the oxidation.