Effect of SiC gradient structure on ablation resistance of (Zr0.25Hf0.25Ti0.25Ta0.25)C multilayer coatings for C/C composites

SiC-coated C/C composites were successively sprayed with (Zr 0.25 Hf 0.25 Ti 0.25 Ta 0.25 )C-30SiC coating and (Zr 0.25 Hf 0.25 Ti 0.25 Ta 0.25 )C coating to form SiC gradient composite coatings from inner layer to outer layer. After ablation above 2100 °C for 90 s, the R l and R m of multilayer (Zr 0.25 Hf 0.25 Ti 0.25 Ta 0.25 )C/(Zr 0.25 Hf 0.25 Ti 0.25 Ta 0.25 )C-30SiC coatings are −1.22 μm·s −1 and −0.636 mg·s −1 , respectively. The excellent ablation property is attributed to the phase evolution of SiC and high entropy carbides during ablation, which forms a four-layer oxide structure with synergistic effects. The diffusion of SiC from (Zr 0.25 Hf 0.25 Ti 0.25 Ta 0.25 )C-30SiC middle layer to oxide layer is guided by sublimation, recrystallization and active oxidation. As SiO 2 diffuses into the ablation layer-II, it favors improving the viscosity of the (Ti/Ta)Ox enrichment areas formed by reversible peritectic transformation of (Zr,Hf) 6 Ta 2 O 17 and Zr( Hf )TiO 4 , effectively maintaining the stability of the interface between the ablative and oxide layers. • SiC gradient structure in (Zr 0.25 Hf 0.25 Ti 0.25 Ta 0.25 )C multilayer coating exhibit lower R l (-1.22 μm/s).