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

Abstract 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.