Microstructure and thermal shock resistance of SiC/CNT-SiC double-layer coating for carbon/carbon composites

To improve the thermal shock resistance of SiC coated carbon/carbon (C/C) composites, a SiC/CNT-SiC double-layer coating has been prepared by depositing carbon nanotubes (CNTs) onto C/C substrate using electrophoretic deposition (EPD) and followed by chemical vapor deposition of SiC. The CNTs are randomly oriented on C/C substrate and form a porous layer. SiC is deposited in the porous CNT layer to form a dense CNT-SiC inner layer, and then is further deposited to form a SiC outer layer. SEM shows that the thickness of CNT-SiC inner layer increases along with the increasing of EPD time from 25 to 85 s. In comparison to the SiC coating without CNTs, the SiC/CNT-SiC coating shows fewer and smaller cracks and better thermal shock resistance. After thermal cycling between 1200 °C and room temperature 15 times, the SiC/CNT-SiC coating with CNTs EPD for 85 s exhibits the best thermal shock resistance, whose weight loss decreases from 15.82% to 11.84%. The improvement of thermal shock resistance can be attributed to the role of CNT-SiC inner layer in alleviating the thermal stress and suppressing the cracks in the coating.