SiC/ZrB₂-SiC-ZrC multilayer coating for carbon/carbon composites against ablation

To improve the ablation resistance of carbon/carbon (C/C) composites at high temperature, a ZrB₂-SiC-ZrC coating was prepared on the surface of SiC-coated C/C composites by supersonic atmosphere plasma spray (SAPS). Ablation resistance of the coated C/C composites was tested in an oxyacetylene torch environment with a heat flux of 2400 kW/m² for 120, 150 and 200 s, respectively. After ablation for 120 s, the coating exhibited a three-layered structure consisting of a porous ZrO₂ layer, a ZrO₂-SiO₂ thin layer and a SiC-depleted layer, whereas it transformed into a two-layered structure (ZrO₂ recrystallized layer and ZrO₂-SiO₂ layer) after ablation for 150 s. With the increase of ablation time, the SiC inner coating was almost consumed and a gap emerged between the ZrO₂ layer and the C/C matrix after ablation for 200 s. The good ablation resistance of the sprayed coating is mainly attributed to the layered structure acting as a thermal barrier and inhibiting inward diffusion of oxygen.