Preparation,ablation behavior and mechanism of C/C-ZrC-SiC and C/C-SiC composites

ZrC precursor was synthesized by a solution approach using ZrOCl₂·8H₂O, acetylacetonate, glycerol and boron-modified phenolic resin. A ZrC yield of ~ 40.56 wt% was obtained at 1500 °C in the C/Zr molar ratio of 1:1. C/C-ZrC-SiC composites were fabricated by a combined processes of chemical vapor infiltration (CVI) and precursor infiltration and pyrolysis (PIP) using the synthesized ZrC precursor. For comparison, C/C-SiC composites were prepared by CVI. Thermogravimetric analysis showed that C/C-ZrC-SiC composites exhibited better oxidation resistance than C/C-SiC composites. After oxyacetylene torch ablation, the mass ablation rate of C/C-ZrC-SiC composites was 9.23% lower than that of C/C-SiC composites. The porous ZrO₂ skeleton in the ablation center was prone to be peeled off by the flame flow, resulting in the higher linear ablation rate of C/C-ZrC-SiC composites. The oxide layers of ZrO₂ and SiO₂ were formed on the transition and brim region of C/C-ZrC-SiC composites and acted as effective heat and oxygen barriers. For C/C-SiC composites, the C-SiC matrix was severely depleted in the ablation center and the formed SiO₂ layer in the brim region could protect the matrix against further ablation.     

Microstructure and ablation mechanism of C/C-ZrC-SiC composites in a plasma flame

Ablation behavior of C/C-ZrC-SiC composites was investigated using a plasma flame. The composites exhibited excellent ablation performance. After ablation for 180 s, three kinds of ablation behavior appeared from the border to the center on the surface, which were closely related to the temperature and denudation force. Additionally, the ablation behavior in the cross-sectional direction of the composites was mainly controlled by the temperature. During the ablation, ZrC and SiC were oxidized into ZrO₂ and SiO₂, respectively, resulting in the formation of a ZrO₂-SiO₂ binary eutectic system. The ablation mechanism was also discussed, which could provide strong illustration of the evolution processes of the eutectic system at different temperatures.     

Ablative property and mechanism of SiC-CuxSiy modified C/C-ZrC composites prepared by a rapid method

A rapid method was developed to fabricate C/C-ZrC-SiC-Cu_xSi_y composites with low open porosity by precursor infiltration and pyrolysis combining with pressure assisted reactive melt infiltration. Dominant phases of ZrC and SiC with scattered Cu_xSi_y inclusions were present in continuous infiltrated matrix, in which the dimension of submicron ZrC particles displayed gradient change. At ablation test, the heat absorbing effect of Cu_xSi_y-phase and formation of protective ZrO₂-SiO₂ cover enhanced the ablative property of composites for short-time ablation, causing ablation rates of 30 s ablation reached 1.7 ± 0.1 µm/s and 1.3 ± 0.1 mg/s, respectively. As ablation time extends to 60 s, the massive consumption of Si-phase damaged the integrity of surface oxide cover, but the partial melted ZrO₂ improved the viscosity and self-healing ability of ZrO₂-SiO₂ mixture, protecting substrate from further erosion. Thus, ablation rates were increased and decreased to 3.8 ± 0.2 µm/s and 1.2 ± 0.1 mg/s, respectively.     

Ablation behavior of a C/C-ZrC-SiC composite based on high-solid-loading slurry impregnation under oxyacetylene torch

A C/C-ZrC-SiC composite was successfully prepared by high-solid-loading slurry impregnation combined with polymer infiltration and pyrolysis. The microstructure and ablation behavior of the C/C–ZrC–SiC composite were investigated. ZrC particles were uniformly distributed in the matrix, and the obtained C/C–ZrC–SiC composite had a high density of 2.74 g/cm³. After exposure to oxyacetylene flame with a heat flux of 3.86 MW/m² for 120 s, the mass and linear ablation rates of the composite were 0.72 ± 0.11 mg/s and 0.52 ± 0.09 µm/s, respectively. The excellent ablation properties of the composite were attributed to the protection of the matrix by a three-layered oxide scale consisting of ZrO₂/SiO₂-rich/ZrO₂-SiO₂.     

A novel Cr-doped Al2O3-SiC-ZrC composite coating for ablative protection of C/C-ZrC-SiC composites

A novel Cr-doped Al₂O₃-SiC-ZrC coating systemis proposed to further improve the ablation resistance of C/C-ZrC-SiC composites. Our approach combines low pressure plasma spray method with slurry impregnation of Zr-Cr-Si-C to achieve a specially tailored oxide-carbide structure. Results show that the as-prepared coating was dense and crack-free, which effectively promoted the ablation resistance of C/C-ZrC-SiC with the mass and linear ablation rates decreased by 66% and 76% respectively, involving a highly dense protective structure of A1_xCr_2-xO₃-SiO₂-ZrO₂ formed during ablation. The compact and continuous multi-oxide scale with “ZrO₂-rosette” skeleton intricated with A1_1.96Cr_0.04O₃ was evidenced in the ablation center.     

Novel one-step formed composite reinforcement of "Spider web like" SiCnw networks and "Z-pins like" SiC rods for ablation resistance improvement of C/C-ZrC-SiC

A novel composite reinforcement with horizontal multilayer "Spider web like" SiC nanowire networks and vertical interconnected "Z-pins like" SiC rods was designed and prepared by facile one-step figuration. The linear ablation rate of "Spider web like" SiC nanowire networks and "Z-pins like" SiC rods collectively reinforced C/C-ZrC-SiC composites at 2610 ± 20 ℃ was 0.4 ± 0.03 μm/s with a 74.19 % reduction. The improved ablation resistance was attributed to a denser gradient oxide layer composed of central ZrO₂ layer, transitional ZrO₂-SiO₂ layer and marginal SiO₂ layer generated under the initial sticky net effect from SiCnw networks and subsequent oxide compensation from "Z-pins like" SiC rods.     

Ablation behavior of C/SiC with YSZ and ZrB2 coatings under high-energy laser irradiation

Carbon fiber-reinforced silicon carbide (C/SiC) composites are important candidates for laser protection materials. In this study, ablation mechanism of C/SiC coated with ZrO₂/Mo and ZrB₂–SiC/ZrO₂/Mo under laser irradiation was studied. ZrB₂–SiC multiphase ceramic and ZrO₂ ceramic were successfully coated on C/SiC composite by atmospheric plasma spraying technology with Mo as transition layer. Phase evolution and morphology of composite were investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Moreover, ablation behavior of the composite was investigated by laser confocal microscopy. Results showed that ablation mechanism of C/SiC composite was controlled by phase transformation, thermal reaction, and thermal diffusion, with solid–liquid transition of ZrB₂ and ZrO₂ being dominant factor. Endothermic reaction and good thermal diffusivity of coatings were also important factors affecting ablation performance. Reflectivity effect of ZrO₂ coating was limited under high-energy laser irradiation. Compared with ZrO₂/Mo single-phase-monolayer coating, designed ZrB₂–SiC/ZrO₂/Mo coating showed better ablation performance, and breakdown time of C/SiC increased from 10 to 40 s. The depletion of liquid phase in molten pool was identified as an important factor responsible for rapid failure of C/SiC. The coating failed when the entire liquid phase was consumed within molten pool, followed by rapid damage of C/SiC substrate. Results of this study can provide theoretical guidance and research ideas for design and application of laser protective materials.     

Cyclic ablation behavior of mullite-modified C/C-HfC-SiC composites under an oxyacetylene flame at about 2400 °C

Mullite-modified C/C-HfC-SiC composites were prepared via precursor infiltration and pyrolysis (PIP). The phase composition, microstructure, and cyclic ablation behavior under oxyacetylene flame with a heat flux of 4.18 MW/m² were investigated, and a comparison with the C/C-HfC-SiC composites showed that the mullite-modified composites have better ablation resistance. Results displayed a HfO₂ skeleton structure wrapped by SiO₂ and a dense layer of HfO₂-SiO₂ in the center and transition regions after the first ablation for 30 s, respectively. The structures transformed into HfSiO₄-wrapped carbon fibers and "island" shape HfO₂-HfSiO₄-SiO₂ layer after the second ablation for 30 s. Then both structures underwent severer peeling of HfSiO₄ and consumption of SiO₂ after the third ablation for 30 s. The modified composites exhibited better mass ablation rates after forming HfSiO₄, which were 0.36 mg/s cm² and 0.38 mg/s cm², respectively.     

The ablation behavior and mechanical property of C/C-SiC-ZrB2 composites fabricated by reactive melt infiltration

In order to improve the ablation resistance of carbon/carbon (C/C) composites, SiC-ZrB₂ di-phase ceramic were introduced by reactive melt infiltration. The ablation properties of these composites were evaluated by oxyacetylene torch with a heat flux of 2.38 MW/m² for 60 s. Compared with the pure C/C composites, the C/C-SiC-ZrB₂ composites show a significant improvement in the ablation resistance, and the linear and mass ablation rates decreased from 10.28×10⁻³ mm/s to 6.72×10⁻³ mm/s and from 3.08×10⁻³ g/s to 0.61×10⁻³ g/s, respectively. After ablation test, the flexural strength retentions of the C/C and C/C-SiC-ZrB₂ composites near the ablated center region are 39.7% and 81.6%, respectively. The higher strength retention rate of C/C-SiC-ZrB₂ composites was attributed to the introduction of SiC-ZrB₂ ceramic phases, which have excellent ablation resistant property. During ablation test, an ‘embedding structure’ of Zr-O-Si glass layer was formed, which could act as an effective barrier for oxygen and heat. The oxide ceramic coating could protect the C/C-SiC-ZrB₂ composites from further ablation, and thus contribute to retaining the mechanical property of C/C-SiC-ZrB₂ composites after ablation.     

Effect of zirconia on ablation mechanism of asbestos fiber/phenolic composites in oxyacetylene torch environment

Micron-size zirconium oxide (ZrO₂) was used to improve the thermal stability and ablation properties of asbestos fiber/phenolic composites and to reduce their final cost. ZrO₂/asbestos/phenolic composites were prepared in an autoclave by the curing cycle process. The densities of the composites were in the range of 1.64–1.82 g/cm³. The ablation properties of composites were determined by oxyacetylene torch environment and burn-through time, erosion rates and back surface temperature in the first required 20 s. To understand the ablation mechanism, the morphology and phase composition of the composites were studied by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Thermal stability of the produced materials was estimated by means of thermal gravimetric analysis, in air which consisted of dynamic scans at a heating rate of 10 °C/min from 30 to 1000 °C with bulk samples of about 23±2 mg. The thermal stability of the composites was enhanced by adding ZrO₂. The results showed that the linear and mass ablation rates of the composites after adding 14 wt% ZrO₂ decreased by 58% and 92%, respectively. The back surface temperature of a sample with 14% zirconia was 49% lower than that of pure composite. The SEM studies showed that, modified composites displayed much lower porosity than that of non-modified composite and the destruction of asbestos fibers was very low. On the other hand, it appeared that a thin melted layer of ZrO₂ covered the surfaces of zirconia-containing composites.     

Experimental investigation of mechanical,thermal, and ablation performance of ZrO2/SiC modified C-Ph composites

In this study, an effort has been made to improve the mechanical, thermal, and ablation performance of carbon-phenolic (C-Ph) composites. The ZrO₂, SiC, and ZrO₂/SiC hybrid fillers were synthesized using sol-gel method followed by individual incorporation into C-Ph composites. The thermal stability and flexural strength of these C-Ph composites were analyzed using thermogravimetry analysis and three-point bending test, respectively. A significant improvement in the flexural strength and modulus of the reinforced C-Ph composites was observed and also exhibited the higher thermal stability. The oxyacetylene flame test was conducted to measure the ablation behavior of these filler reinforced C-Ph composites under a heat flux of 4.0 MW/m² for 60 seconds. ZrO₂/SiC0.5 reinforcement in the C-Ph composite decreased the linear and mass ablation rates by 46% and 22%, respectively when compared with pure C-Ph composite. The surface morphology analysis revealed that the burnt composite covered with the ZrC ceramic phase and SiO₂ bubble-like structure, which could have improved the ablation resistance of composites. These results were found well within the acceptable range when using the surface energy dispersive spectroscopy and X-ray diffraction analysis.     

Effects of ZrO2 nanoparticles on the microstructure and mechanical properties of ZrO2/AlSi10Mg composites manufactured by laser powder bed fusion

In this work, the nano-ZrO₂ particles were mixed into AlSi10Mg alloy to prepare ZrO₂/AlSi10Mg composites with different x wt.% ZrO₂ (x = 0, 0.15, 0.3, 0.45, 0.6, 0.75). The microstructure, mechanical properties and the anisotropy of the ZrO₂/AlSi10Mg composites fabricated by laser powder bed fusion (LPBF) were studied. The results show that nano-ZrO₂ particles can be uniformly dispersed on the AlSi10Mg powder by the method of pre-dispersion and mechanical mixing. When the mass ratio of ZrO₂ in ZrO₂/AlSi10Mg composites is 0.3 wt%, the values of the tensile strength, yield strength and elongation are 493.64 MPa, 321.30 MPa and 11.74%, respectively. Compared with AlSi10Mg alloy, the tensile strength of ZrO₂/AlSi10Mg composites with 0.3 wt% is increased by 30–55 MPa and the elongation is increased by 3–5%. In addition, the mechanical properties of AlSi10Mg alloy and ZrO₂/AlSi10Mg composites of 0.3 wt% exhibit antistrophic behavior in different direction, which is due to the differences of microstructure, texture and stress distribution between transverse direction (TD) and build direction (BD). Compared with other AlSi10Mg matrix composites, ZrO₂/AlSi10Mg composites of this work show excellent strength and plasticity matching.     

Organic-inorganic composites for novel optical transformation induced by high-energy laser ablation

High-energy continuous-wave (CW) laser has been considered as a significant technology in recent decades. Such laser can destroy conventional materials in an extremely short time, necessitating their protection. In this study, zirconium carbide (ZrC) and silicon carbide (SiC) particle-modified short silicon carbide fiber-reinforced phenolic resin matrix composites (SiC/BPF-ZS) with significant anti-laser performance were designed and prepared. Our results showed that the ceramic particles and SiC fibers rapidly oxidized, leading to the formation of a ceramic coating composed of ZrO₂ and SiO₂. Owing to the formation of the ceramic coating, the reflectivity of the composites improved significantly from 15.8% to 73.2% after ablation at 500 W/cm² for 30 s. Additionally, the SiC fibers played an important role in the formation of a high-reflectivity coating during laser ablation. Contrast experiments indicated that SiC fibers lead to better performance than the carbon fibers. The high reflectivity and low mass ablation rate are demonstrated to be the key factors improving the anti-laser ablation performance of the SiC/BPF-ZS composites.     

Design and preparation of composite coatings with increased reflectivity under high-energy continuous wave laser ablation

High-energy continuous wave (CW) laser ablation can cause severe damage to structural materials in an extremely short time, which generates considerable concern in terms of material safety. For the purpose of reducing or even eliminating such laser-induced damage, a novel composite coating consisting of a boron-modified phenolic formaldehyde resin incorporating ZrC and SiC has been designed and prepared. The experimental results reveal that ZrC and SiC are rapidly oxidized to ZrO₂ and SiO₂ respectively, leading to the formation of a white ceramic layer consisting of ZrO₂ particles and melted SiO₂. After ablation at 1000 W/cm² for 50 s, elemental analysis indicates that no Si can be found in the central ablation zone because of gasification. A relatively compact ZrO₂ layer is formed through the sintering of adjacent ZrO₂ particles, which effectively improves the reflectivity of the coating from 7.3% (before ablation) to 63.5% (after ablation). The high reflectivity greatly reduces the absorption of laser energy. In addition, no obvious ablation defects are observed in the composite coating. The excellent anti-laser ablation performance of the coating makes it a promising system for protecting a material against the effects of long-term CW laser ablation.     

Intelligent cooling structure design of "Z-pins like" silicon rods to enhance the ablation resistance of C/C-ZrC-SiC composites above 2500 °C

In order to improve the ablation resistance of C/C-ZrC-SiC composites by reducing the damage of the protective oxide layer, novel "Z-pins like" silicon rods, which were designed and fabricated by liquid phase sintering, were utilised as a dissipative agent. The microstructure evolution and thermal dissipation behaviour were investigated after ablating above 2500 °C for 300 s. After the "Z-pins like" silicon rods were implanted, the anti-ablative property of the C/C-ZrC-SiC composites was drastically improved by the dissipative thermal protection mechanism. The linear ablation rate of the "Z-pins like" silicon rod-reinforced C/C-ZrC-SiC composite was -0.28 μm/s, which is 112.72% lower than the unmodified composite. Additionally, the actual ablative temperature dropped approximately 357 °C, which enabled abundant SiO₂ to remain in the ablation centre. Furthermore, a dense SiO₂-rich oxide layer with a low oxygen diffusion coefficient is formed that covers the entire ablative surface.     

Effects of preform structures on the mechanical and ablation properties of C/ZrC-SiC composites

In order to investigate the effects of preform structures on the mechanical and ablation properties of C/ZrC-SiC composites, 3D4X, 3D5X and 3DZC C/ZrC-SiC composites were fabricated with the same process. The mechanical and ablation properties of 3D4X, 3D5X, and 3DZC C/ZrC-SiC composites were investigated. Results showed that the tensile strength (122.26 MPa) and bending strength (233.29 MPa) of 3D5X C/ZrC-SiC composites were the largest, followed by the tensile strength (112.79 MPa) and bending strength (203.03 MPa) of 3DZC composites and the tensile strength (86.22 MPa) and bending strength (137.59 MPa) of 3D4X composites. The mechanical properties of C/ZrC-SiC composites were mainly related to the fiber content in the axis direction and matrix compactness. In terms of ablation properties, 3DZC C/ZrC-SiC composites acted out the worst performance (the linear ablation rates of 0.0293 mm/s and the mass ablation rates 0.00766 g/s), followed by 3D4X composites (the linear ablation rates of 0.0276 mm/s and the mass ablation rates 0.00683 g/s) and 3D5X composites (the linear ablation rates of 0.0175 mm/s and the mass ablation rates 0.00653 g/s), respectively, which were mainly due to the specific ablation angles, thermal conductivities, and ablation oxides contents caused by fiber volume fraction, braided angles, and other forming parameters.     

Fabrication of structure-controlled hydroxyapatite/zirconia composite

The structure-controlled hydroxyapatite/zirconia (HAp/ZrO₂) composites were fabricated. At first, cylindrical hydroxyapatite (HAp) samples were prepared by the extrusion process, and then the extruded HAp cylindrical samples were coated with 3 mol% of Y₂O₃ partially stabilized ZrO₂ slurry, dried and aligned unidirectionally to form a composite bulk. The volume fraction of ZrO₂ in the HAp/ZrO₂ composite was estimated to be about 23 vol%. Bulk density and bending strength of the composites increased with sintering temperature. Fracture energy of HAp/ZrO₂ composite sintered at 1350 °C was approximately 1.6 times higher than that of monolithic HAp. Although the bending strength of HAp/ZrO₂ composite prepared in this study was relatively low, it exhibited high fracture energy than HAp monolithic and a non-brittle fracture behavior was obtained without using fiber as the reinforcement.     

Additively-manufactured multiphase coatings with laser protection ability for the repairing of MoSi2-SiC/SiC coated C/C composites

The Si-SiC-MoSi₂ and Si-SiC coatings were proposed to repair the damaged MoSi₂-SiC/SiC coated C/C composites by laser directed energy deposition. Laser ablation was used to assess the repair effect. Results showed that both the repaired coatings with dense structure could restore the geometric size of damaged area. Compared with the Si-SiC-MoSi₂ coating, the Si-SiC repaired coating with higher laser reflectivity and more free Si could reduce the heat generation and enhance the heat dissipation during ablation, which lowered the maximum temperature by 347.49 K and 810.77 K under 300 W and 500 W ablation for 7 s separately, beneficial to avoid the secondary laser damage of the repaired area.     

A novel design of Al-Cr alloy surface sealing for ablation resistant C/C-ZrC-SiC composite

To improve anti-ablation property of C/C-ZrC-SiC composite, a novel design of Al-Cr alloy surface sealing was performed by liquid melt impregnation. Results show that Al₈Cr₅ formed on the surface which could effectively seal the holes and cracks. The cooperation of metal and ceramics contribute a better anti-ablation performance to the obtained composite, and its mass and linear ablation rates decrease by 98.3% and 81.2% respectively. This special surface structure evolves into a highly dense oxide scale comprising various solid solutions (including Al-Cr-O, Al-Si-O, Cr-Si-O) and ZrO₂, which could significantly improve the anti-ablation performance of C/C-ZrC-SiC composite.     

Effect of ZrC amount and distribution on the thermomechanical properties of Cf/SiC-ZrC composites

C_f/SiC-ZrC composites with different amounts and distributions of ZrC were fabricated by polymer impregnation and pyrolysis. The effects of the ZrC amount and distribution on the microstructural, mechanical, and ablation properties of C_f/SiC-ZrC composites were investigated. C_f/SiC-ZrC composites obtained by the alternating infiltration of ZrC organic precursors and polycarbosilane groups exhibit good tensile strength (240 ± 17.7 MPa) because the ZrC and SiC matrix can mix evenly. However, C_f/SiC-ZrC composites using only ZrC organic precursor infiltration show a low tensile strength (191 ± 16.6 MPa) because more defects can be introduced into the composites. Ablation characterization by a 30 kW plasma wind tunnel for 60 seconds showed that the C_f/SiC-ZrC composites with the highest amount of ZrC matrix (67.8 wt.%) possessed the lowest linear erosion rate of 4 μm/s because liquid SiO₂ could fill the porous ZrO₂ to form a homogenous protective layer. Nevertheless, the C_f/SiC-ZrC composites with a relatively high ZrC amount (55.3 wt.%) exhibited a poorer ablation performance compared to that of C_f/SiC-ZrC composites with a low ZrC amount (38.7 wt.%).