ZrB2-SiC coating to protect carbon/carbon composites against ablation

To improve the ablation resistance of carbon/carbon (C/C) composites, a ZrB2-SiC coating was prepared by pack-cementation. The phase composition, microstructure and element distribution of the coating were analyzed using X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. The coated sample exhibits a dense structure and has an outstanding ablation property. During exposure to the oxyacetylene flame at about 2000 K for 40 s, the coated sample had a linear ablation rate of 4.4 x 10(-3) mm/s and a mass ablation rate of 6.2 x 10(-5) g/s. Compared with the uncoated C/C composites, the linear and mass ablation rate decreased by 49% and 97%, respectively. During the oxyacetylene torch test, a silica-scale glass was generated on the surface of the coating, and the embed ZrO2 could provide pinning effect to avoid cracking and spalling of the silica-scale glass. After the ablation test, some silica nanowires (SiONWs) were found in the ablation edge region of the sample. The growth mechanism of SiONWs consists of oxide-assisted growth (OAG) and vapor-liquid-solid (VLS) formation. (c) 2013 Elsevier B.V. All rights reserved.