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In this work, AlN whisker-reinforced (Zr, Hf)O 2 coating was prepared on SiC coated carbon/carbon composites by sol-gel and plasma spraying methods. Its cyclic ablation resistance was evaluated using an oxyacetylene torch with a heat flux of 2.38 MW/m2. After ablation, the coating showed apparently decreased crack sizes and quantity as compared with the one without AlN whisker addition, pointing out its better crack tolerance. Moreover, the coating had a thinner oxidized region based on the linear ablation rate (−0.042 µm/s), greatly lower than that of pure oxide coating (−0.922 µm/s). After detailed observation and characterization, probable protection mechanism was proposed. [ABSTRACT FROM AUTHOR]

There is an urgent need for the thermal protection of carbon/carbon composites to increase their service span in aerospace field. As members of ultra-high temperature ceramics, HfC and ZrC are thought to be alternative materials, but their poor oxidation behavior and fracture toughness at temperature over 2000 ℃ prevent them from taking full advantages. Herein, we synthesized nanosized Hf 6 Ta 2 O 17 powders and introduced them into HfC ceramic to tackle the above problems. Plasma-sprayed HfC coatings with Hf 6 Ta 2 O 17 varied from 0 to 15 mol.% (0, 1.25, 2.5, 5, 15) were exposed to an oxyacetylene torch with a heat flux of 2.38 MW/m2. The one with 2.5 mol.% Hf 6 Ta 2 O 17 showed the best ablation resistance. Smaller doping was unable to effectively hinder oxygen diffusion given the inadequate compactness of the formed scale, conversely substantial humps and ruptures formed on the samples with higher amounts, acting as straightforward paths for oxygen. • Nanosized Hf 6 Ta 2 O 17 powders were synthesized using sol-gel method. • HfC coatings with various Hf 6 Ta 2 O 17 amounts were fabricated on carbon/carbon composites by plasma spraying. • The sample containing 2.5 mol.% Hf 6 Ta 2 O 17 was supposed as the one with the best ablation resistance. • The ablation mechanisms of the samples were proposed based on the microstructure changes. [ABSTRACT FROM AUTHOR]

Based on the investigation of ablation behavior and thermal stress of the monolayered ZrC-SiC coatings with different SiC amounts, an alternate coating consisting of 4 sublayers with 10 and 70 vol.% SiC was prepared on SiC-coated carbon/carbon (C/C) composites through plasma spraying technique. Ablation tests were carried out under oxyacetylene torch with a heat flux of 2.38 MW/m2. The alternate coating could offer 90 s ablation shield for C/C composites, providing superior ablation properties than all monolayered coatings. The improved ablation resistance is mostly induced by the fact that the outmost scale with abundant ZrO 2 particles was able to better endure the mechanical denudation from the torch. Moreover, due to the indirect contact with torch, the innermost sublayers were placed into relatively mild environment, thereby most of Si-based oxides could be retained and further hinder oxygen transport inward during ablation. [ABSTRACT FROM AUTHOR]

In this work, ZrO 2 with different ZrB 2 contents (0, 15, 30,40 wt%) composite powders were synthesized by sol-gel, then they were sprayed on carbon/carbon composites using plasma spraying to construct a three-dimensional (3D) thermal conduction network within the formed coating. Oxyacetylene ablation tests were carried out under 4.2 MW/m2 to investigate the effect of the 3D thermal conduction network on the ablation resistance of coated samples. The encapsulation structure formed during sol-gel process benefits to slowing the oxidation rate of ZrB 2 and the content of ZrB 2 is critical for establishing a stable 3D thermal conduction network within the coating. • ZrO 2 -encapsulated ZrB 2 powders were fabricated and sprayed on the surface of C/C composites. • The 3D thermal conduction network was constructed in the formed coating. • The ablation resistance of coated samples was evaluated under a heat flux of 4.2 MW/m2. • The coating with 3D thermal conduction network sustained a milder environment and exhibited better ablation resistance. [ABSTRACT FROM AUTHOR]

In this work, ZrC and ZrO 2 coatings were prepared on SiC-coated carbon/carbon (C/C) composites by supersonic atmospheric plasma spraying. Their ablation behavior was investigated and compared under different heat fluxes to design multilayer anti-ablation structural coating. Results shown that ZrO 2 coating exhibited denser oxide layer and lower mass consumption after ablation. According to their microstructure and thermal analysis, possible reasons can be ascribed to higher surface temperature and lower melting point of ZrO 2 coating, which made the scale easier to be sintered during ablation. Moreover, the ablated ZrC coating presented particle accumulation structure at the initial ablation stage, hence causing the consumption from mechanical denudation to occur in these particles preferentially rather than sintering. [ABSTRACT FROM AUTHOR]

HfC-TaC/HfC-SiC alternate coatings with different sublayer thicknesses were fabricated on SiC-coated carbon/carbon composites by supersonic atmosphere plasma spraying. Their ablation resistance was studied under oxyacetylene torch and compared with monolayered HfC-TaC coating. The alternate coating with 6 spray cycles of HfC-TaC and 3 spray cycles of HfC-SiC sublayers exhibited the best ablation performance as confirmed by the integral coating morphology and the lowest ablation rates. A dense oxide layer acting as an oxygen insulator and the release of thermal stress induced by the formation of dendritic cracks are thought to be responsible for its great ablation resistance. For the alternate coating with 4 spray cycles of HfC-TaC and 2 spray cycles of HfC-SiC sublayers, exfoliation occurred at the interface of two adjacent sublayers, leading to violent evaporation of exposed HfC-SiC sublayer. [ABSTRACT FROM AUTHOR]

Several multilayer architectures, based on ZrC-SiC system, were fabricated on SiC-coated carbon/carbon composites by plasma spraying and tested using an oxyacetylene torch. A remarkable variance in scale evolution was found in these multilayer coatings, referring to close correlation between multilayer architecture and ablation behavior. The multilayer coating made of consecutive sublayers of ZrC-10, 30, 10 and 70 vol% SiC survived three repeated ablation cycles with mass ablation rate of −0.467 mg/s and linear ablation rate of − 0.411 µm/s. Detailed phase analysis and morphology investigation attributed its preferable ablation performance to the formation of multifunctional scale and modest thermal stress. • Various ZrC-SiC multilayer coatings were prepared on SiC-coated C/C composites by plasma spraying. • The relationship between coating architecture and ablation behavior was studied using oxyacetylene torch. • Ablation mechanism was analyzed systematically as well as the roles of different sublayers. • Theoretical analysis was adopted to compare the stress level within these multilayer coatings. [ABSTRACT FROM AUTHOR]

Aiming to ameliorate the rapid oxidization and deterioration of carbon/carbon (C/C) composites in extreme environments, a novel multilayer coating containing ZrO 2 -Y 2 O 3 , ZrC-ZrO 2 and ZrC-SiC layers from surface to inside was prepared on SiC-coated C/C composites via plasma spraying. Its scale evolution was studied under exposure to an oxyacetylene torch above 2000 ℃. Only the multilayer coating survived after ablation for 90 s × 2 and maintained an integrated appearance, whereas the other monolayered coatings were failure prematurely. The monotonically decreased thermal expansion and multiple roles gathering thermal shield, crack termination and oxidation retardation accounted for its preferable ablation resistance. • A novel zirconium-based multilayer coating was fabricated on SiC-coated C/C composites by plasma spraying. • It owned preferable ablation property than monolayered coatings under exposure to oxyacetylene torch. • Monotonically reduced thermal expansion lessened the detrimental effect of cracks. • The scale with multiple characters including thermal shield, gradient and oxidation retardation accounted for its high protection. [ABSTRACT FROM AUTHOR]