Response mechanism study of alternate ZrC-10vol.% SiC/ZrC-70vol.% SiC coatings with various sublayer thicknesses for cyclic and long-term thermal exposure.

• Alternate coatings with various sublayer numbers were prepared on SiC coated C/C composites using SAPS. • As the alternate number rises, the coating behaved better thermal shock resistance. • The coating with 6 sublayers could offer more than 240 s ablation retardation for the substrate with no visible flaws yielded. • The formed scale with alternate dense/porous structure was capable of not only resisting oxygen diffusion but also weakening the thermal stress. To explore the influence of sublayer numbers on the structure evolution and thermal stress level, an alternate coating consisting of ZrC-10 vol.% SiC and ZrC-70 vol.% SiC sublayers was designed in this work. With a basically consistent general thickness, three coatings constituted by 2, 4 and 6 sublayers were prepared by plasma spraying, which then were assessed using an oxyacetylene torch under cyclic and long-term exposure. The coating with 6 sublayers was supposed to be the one with the best ablation property, finite element analysis also evidenced its least thermal stress among all these samples. After being ablated for 240 s, the linear and mass ablation rates of the coating with 6 sublayers decreased by 51.27% and 14.41% as compared to that with 4 sublayers. Post-test analysis proved the existence of Si-based products, which help the outmost surface to develop a dense profile. Additionally, the yielded alternate dense/porous scale had a preferable toughness, allowing it to maintain a good integrity. [ABSTRACT FROM AUTHOR]