Microstructure and resistance to thermal shock of SiC coatings that are prepared on C/C-composite pyrocarbon matrices of various textures

Abstract

SiC coatings were prepared on rough laminar (RL) pyrocarbon and smooth laminar (SL) pyrocarbon matrices of carbon/carbon composites with pack cementation via the same process. The influence of the pyrocarbon texture on the thermal shock properties and, where relevant, the microstructures of the coatings were explored. The results demonstrated that the RL-SiC (RLS) coating consisted of large SiC particles compared with the SL-SiC (SLS) coating. The thicknesses of the RLS coating and SLS coating were 288 μm and 121 μm, respectively. At 1500 °C, the RLS coating had a mass loss of 0.29% after 30 cycles, while the mass loss of the SLS coating was 2.01%. The original cracks, which had widths of approximately 3.0 μm, on the RLS coating and the SLS coating could seal quickly and had no catastrophic consequences on the coating thermal shock property. The thermal shock RLS-coated specimen performed well since the rough laminar pyrocarbon had a similar coefficient of thermal expansion to SiC, which was crucial for decreasing the microcrack production. Moreover, the rough laminar pyrocarbon easily reacted with silicon, which was advantageous for the formation of thick coatings and provided durability under thermal shock conditions.