Ablation performance of rare earth oxide (REO)-stabilized tetragonal and cubic zirconia coatings as a thermal protection system (TPS) for carbon/carbon composites

To protect carbon/carbon (C/C) composites from severe oxidation and ablation at temperatures exceeding 500 ℃ during the hypersonic applications, a novel Sm2O3-stabilized ZrO2 coating is applied using atmospheric plasma spray. The surface was pre-treated with an oxyacetylene flame to increase the surface roughness and, therefore, to create geometric textures known as anchors. The non-equilibrium tetragonal (t΄) ZrO2 coating stabilized with 6 mol% Sm2O3 offered the best ablation resistance, with survivability maintained through 120 s of ∼390 W/cm2 heat flux oxyacetylene ablation heating without any denudation from the C/C substrate. The coating significantly improved the ablation resistance of C/C by reducing the mass ablation rate by ∼71% and the linear ablation rate by ∼94%. Despite a significant thermal expansion coefficient mismatch between the substrate and the coating, a well-defined mechanical adhesion characterized by the anchors was observed in pre- and post-ablated coating microstructures, indicating its influence in improving ablation resistance.