Facile preparation of a SiC@SiO₂ nanowire-toughened ZrB₂–SiC/SiC bilayer coating with good interfacial bonding, high toughness, and excellent cyclic ablation resistance on C/CA composites

Preparing antioxidant coatings to address the inherent oxidation sensitivity of carbon fiber-reinforced carbon aerogel (C/CA) composites is a feasible way to promote their application in oxidizing environments as thermal insulation materials. However, preparing the coatings with excellent oxidation and ablation resistance while avoiding evident damage to the C/CA substrate still remains a challenge. Herein, a SiC@SiO₂ nanowire-toughened ZrB₂–SiC/SiC bilayer coating with a large thickness of 500 μm was prepared on C/CA using a one-step low-temperature reaction sintering method, which simultaneously formed a sintered outer layer with even-distributed nanowires and a siliconized gradient inner layer. By courtesy of the synergic thermal response of the layers and the crack deflection induced by the nanowires, the resulting coating has moderate residual compressive stress of 0.08–1.22 GPa in the interface, high interfacial bonding strength of 6.02 MPa, and good fracture toughness of 4.36 MPa·m^1/2. Benefited from the optimum components and improved structure, the coating shows excellent cyclic ablation resistance with linear ablation rates of 0.1 μm/s at 1650 ℃ for 1500 s (300 s × 5 cycles) and 0.4 μm/s at 1850 ℃ for 900 s (300 s × 3 cycles). The one-step preparation strategy contributes to little damage to the substrate, thus showing the well-preserved mechanical and thermal insulation properties.