Bimodal microstructure ZrB2-MoSi2 coating prepared by atmospheric plasma spraying for carbon/carbon composites against long-term ablation

To protect carbon/carbon composites against long-term ablation, a bimodal microstructure ZrB2-MoSi2 coating, consisting of an outer ZrB2-MoSi2 layer modified by Y2O3 and an inner basal ZrB2-MoSi2 layer, was prepared by atmospheric plasma spraying. The microstructure, phase composition and ablation resistance of the proposed coating were investigated in detail. Results showed that the bimodal coating maintained integrity in structure except for phase composition. There was no visible interlayer between the inner ZrB2-MiSi2 layer and the outer modified one. Mass ablation rate of the bimodal microstructure ZrB2-MoSi2 coated C/C composites was −2.02 × 10−3 g/s under an oxyacetylene flame ablation at 1873 K for 600 s, which exhibited better ablation resistance than a single ZrB2-MoSi2 coating. The excellent ablation resistance was ascribed to the positive effect of Y2O3, which not only pined in the glassy phase and alleviated the volatilization of SiO2 glass phase by reacting with SiO2 to form high viscosity of Y2SiO5, but also stabilized ZrO2 and promoted its recrystallization and growth.