The mechanical properties of C/C-ZrC-SiC composites after laser ablation

Considering practical environment, the bending property of C/C-ZrC-SiC, C/C-SiC and C/C composites after ablation was worthily studied. Results revealed that C/C-ZrC-SiC composites had a better laser ablation resistance and higher bending strength retention compared with C/C-SiC and C/C composites. The mass loss rate and ablated depth of C/C-ZrC-SiC composites was − 0.09% and 190.377 μm, respectively. The retention of bending strength of C/C-ZrC-SiC composites was 217.67 ± 44.12 MPa, whose strength decreased by 3.57% compared with that of as-prepared C/C-ZrC-SiC composites. The excellent anti-ablation property and residual bending strength of C/C-ZrC-SiC composites were attributed to the lowest ablative temperature and the effective protection of the ZrO₂ grain and ZrO₂-SiO₂ layer, which were formed by oxidation of ZrC-SiC, evaporation of SiO₂, migration of liquid ZrO₂-SiO₂ and the infiltrated as well as grown ZrO₂. However, the fracture behavior transformation of composites from pseudo-plastic rupture to brittle rupture was induced by the ablation damage.     

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.     

Ablation properties of C/C-UHTCs and their preparation by reactive infiltration of K2MeF6 (Me = Zr,Ti) molten salt

Ultra-high temperature ceramic-modified C/C composites (C/C-UHTCs) were prepared by the reactive infiltration of K₂MeF₆ (Me = Zr, Ti) mixed with Si and Zr-Si powders. Molten salt infiltration can be divided into two stages: salt ion melt and Me-Si alloy melt. In the temperature range below 1400 °C, Zr and Si dissolve in the molten salt, are carried by the ion melt, and precipitate at the PyC interface to form carbides. Above 1400 °C, a large amount of molten salt volatilises and thermally decomposes. The Me-Si alloy forms a melt and infiltrates the C/C matrix, and finally forms C/C-ZrC-SiC, C/C-Ti₃SiC₂-SiC, and C/C-ZrC-TiC-SiC composites. The C/C-ZrC-SiC composite with the highest ZrC content exhibited the lowest mass rate (2.6 ± 0.02 mg/s) and linear ablation rate (0.82 ± 0.04 μm/s), which were reduced by 43.5 and 50.8 %, respectively, compared to the unmodified C/C-ZrC-SiC composite.     

Infrared radiative performance and anti-ablation behaviour of Sm2O3 modified ZrB2/SiC coatings

To improve the emissivity of ZrB₂/SiC coatings for serving in more serious environment, ZrB₂/SiC coatings with varying contents of high emissivity Sm₂O₃ were fabricated using atmospheric plasma spraying. The microstructure, infrared radiative performance and anti-ablation behaviour of the modified coatings were investigated. The results showed that as the content of Sm₂O₃ increased, the density of the coatings increased because of the low melting point of Sm₂O₃. When the content of Sm₂O₃ was 10 vol%, the coating had the highest emissivity in the 2.5–5 μm band at 1000 °C, up to 0.85, because of the oxygen vacancies promoting additional electronic transitions. Due to the high emissivity, the surface temperature of the coating modified with 10 vol% Sm₂O₃ decreased by 300 °C, which led to little volatilisation of the sealing phase. Further, the mass ablation ratio of the above coating was 3.19 × 10^?4 g/s, decreasing 31% compared to that of a ZrB₂/SiC coating. The formed dense surface structure of the coatings showed considerable oxygen obstructive effects. These findings indicate that the modified coatings show considerable anti-ablation performance, which provides effective anti-ablation protection for the C/C composite substrate.     

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.     

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.     

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.     

Effects of surface structure unit of 2D needled carbon fiber preform on the microstructure and ablation properties of C/C-ZrC-SiC composites

To investigate the effects of different structure units on the ablation properties of C/C-ZrC-SiC composites produced from 2D needled carbon fiber preforms as reinforcements, non-woven layer, short-cut fiber web and the surface of laminated layers of the composites were ablated by oxyacetylene flame respectively. Results showed that the formation ability of surface protective layer and the fiber orientation were the key factors, determining ablation properties of different structure units. Short-cut fiber web presented the best ablation resistance due to the forming of compactly integrated ZrO₂ self-protection coating because of its sufficient ceramic content. However, only scattered oxide particles formed on the ablated surface of non-woven layer, which resulted in serious erosion of carbon fibers and carbon matrices, leading to the poor ablation resistance. Compared with the non-woven layer perpendicular to the flame, the anti-ablation property was even worse when it paralleled to the flame.     

Microstructure and ablation behaviors of a novel gradient C/C-ZrC-SiC composite fabricated by an improved reactive melt infiltration

An improved reactive melt infiltration (RMI) route using Zr, Si tablet as infiltrant was developed in order to obtain high-performance and low-cost C/C-ZrC-SiC composite with well defined structure. Two other RMI routes using Zr, Si mixed powders and alloy were also performed for comparison. Effects of different infiltration routes on the microstructure and ablation behavior were investigated. Results showed that C/C-ZrC-SiC composite prepared by Zr, Si tablets developed a dense gradient microstructure that content of ZrC ceramic increased gradually along the infiltration direction, while that of SiC ceramic decreased. Composites prepared by Zr, Si mixed powders and alloy showed a homogeneous microstructure containing more SiC ceramic. In addition, two interface patterns were observed at the carbon/ceramic interfaces: continuous SiC layer and ZrC, SiC mixed layers. It should be due to the arising of stable Si molten pool in the tablet. Among all as-prepared samples, after exposing to the oxyacetylene flame for 60 s at 2500 °C, C/C-ZrC-SiC composite infiltrated by Zr, Si tablet exhibited the best ablation property owing to its unique gradient structure.     

Effect of CrSi2 on the ablation resistance of a ZrSi2-Y2O3/SiC coating prepared by SAPS

To improve the ablation resistance of carbon/carbon (C/C) composites, a proportional amount of ZrSi₂-CrSi₂-Y₂O₃ mixed particles were deposited on the surface of SiC-coated C/C composites by supersonic air plasma spraying (SAPS) to form a ZrSi₂-CrSi₂-Y₂O₃/SiC coating. The microstructure and phase compositions of the coating were studied by SEM, EDS, XRD and its anti-ablation performance was tested by oxyacetylene torch. The experimental results showed that the ZrSi₂-CrSi₂-Y₂O₃ outer coating had a dense microstructure without obvious pores and microcracks, and the thickness reached approximately 150 μm. In the process of being eroded and scoured by the oxyacetylene flame, the coating exhibited excellent anti-ablation property, which was attributed to the mosaic microstructure formed by ZrO₂ and a Si-O-Cr liquid film on the coating surface. After experiencing an ablation time of 80 s, the linear ablation rate and the mass ablation rate of the coating were -1.0 ± 0.03 μm s^-1 and -0.16 ± 0.014 mg s^-1, respectively.     

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.     

Ablation behavior and thermal protection performance of TaSi2 coating for SiC coated carbon/carbon composites

For extending application of TaSi₂ in complex coating system, the ablation behavior and thermal protection performance of TaSi₂ coating is studied to evaluate its potential applications for anti-ablation protection of C/C composites. TaSi₂ coating is prepared by supersonic atmospheric plasma spraying (SAPS) on the surface of SiC coated carbon/carbon (C/C) composites. Phase variation and microstructure are characterized by XRD and SEM, respectively. During the ablation process, the coating is quickly oxidized to SiO₂ and Ta₂O₅ accompanied by a lot of heat consumption. The linear and mass ablation rates are 0.9?µm?s^?1 and ??0.4?mg?s^?1 after ablation for 80?s, respectively Results show that the prepared coating possesses optimal ablation performance under the heat flux of 2.4?MW/m². Moreover, the TaSi₂ coating and SiC inner coating have good chemical and physical compatibility during the ablation process. Therefore, the excellent performance of TaSi₂ coating during the ablation process makes it a candidate for anti-ablation protection for C/C composites.     

Oxidation and ablation behaviours of a SiCnw@SiC–Si coating fabricated for carbon-fibre-reinforced carbon-matrix composites via thermal evaporation and gaseous silicon infiltration

A SiC-nanowire-modified SiC–Si (SiC_nw@SiC–Si) coating was prepared for carbon-fibre-reinforced carbon-matrix (C/C) composites using a two-step method based on thermal evaporation and gaseous silicon infiltration, and the effects of SiC nanowires on the oxidation and ablation behaviours of the coated samples were studied. Oxidation tests conducted at 1500 °C revealed that the weight loss of the SiC–Si-coated C/C composite was 15.85% after 6 h, whereas the SiC_nw@SiC–Si-coated C/C composite experienced a significantly lower weight loss of 1.27% after 50 h. Ablation tests suggested that the mass and linear ablation rates of the SiC_nw@SiC–Si-coated C/C composite were 0.05 mg/s and 0.09 μm/s, respectively; they were reduced by 78.26 and 92.74%, respectively, compared with those of the SiC–Si-coated C/C composite. Careful characterisation suggested that the network structure of the SiC nanowires in the SiC–Si phase can suppress crack propagation and firmly attach to the coating surface to enhance the interfacial adhesion between the coating and substrate, leading to improved anti-oxidation and anti-ablation properties. The SiC_nw@SiC–Si coating could offer a technological foundation for preventing the oxidation and ablation of C/C composites in aerospace engineering.     

Ablation behavior of thin-blade co-deposited C/Cx-SiCy composites under the influence of the complex fluid conditions of the oxyacetylene torch

This paper offers a new way of testing the ablation property of material under an oxyacetylene torch using a thin-blade specimen, which costs much less time to reach the maximum temperature and provides a harsh turbulence fluid field that's closer to reality. The thin-blade specimen experiences a higher turbulent intensity than the traditional disk-like specimen, leading to more efficient heat exchange. The fluid field simulation agrees with the testing results. In addition, we manage to synthesize the C/Cx-SiCy composites with the co-deposition chemical vapor infiltration (CVI) method. The C/Cx-SiCy composites exhibit a similar anti-ablation property as C/C composites and consist of enough SiC phase simultaneously, combining the advantages of both C/C composites and C/SiC composites. The thin-blade C/Cx-SiCy composites show a lower linear ablation rate (1.6 μm/s) than C/C composites (4.1 μm/s) and C/SiC composites (19.6 μm/s) during the oxyacetylene test. The glass layer formed on the surface of C/Cx-SiCy could cling to the bulk material instead of peeling off due to the high PyC content in the matrix could protect the SiO₂ from blowing away.     

C/C composite surface modified by electrophoretic depositing SiC nanowires and its brazing to Nb

A novel surface treatment method by electrophoretic depositing SiC nanowires on the C/C composite was introduced to reinforce the C/C–Nb brazed joints. Results showed that the electrophoretic deposition (EPD) process of SiC nanowires could improve the wettability of the liquid AgCuTi alloy on the C/C substrate because of the reaction between SiC nanowires and active element Ti in the AgCuTi alloy. With the introduction of SiC nanowires, the formation of continuous brittle Ti₃Cu₄ layer was inhibited and the Ti₃Cu₄ changed into lumps. The thickness of the TiC reaction layer was 500 nm when the EPD time was 5s which was larger than that of the original brazed joint. As the EPD time continued to increase, the thickness of the TiC reaction layer decreased gradually and the size of brittle Ti₃Cu₄ phase in the joint became smaller and smaller. With the combined effects of the change in the Ti₃Cu₄ morphology and the TiC reaction layer thickness, the average shear strength of joints achieved a peak of 48 MPa when the EPD time was 30s, which was 60% higher than that of the original brazed joints.     

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.     

Microstructure and ablation property of gradient ZrCSiC modified C/C composites prepared by chemical liquid vapor deposition

Chemical liquid vapor deposition was adopted to fabricate gradient ZrCSiC modified C/C composites, and the microstructure and ablation resistance were studied. Results displayed the content of SiC decreased from the composites edge to the center but that of ZrC increased, indicating SiC and ZrC ceramics have the gradient distribution in the composites. The gradient composites possessed a low CTE and high thermal conductivity. The low CTE restricted the formation and expansion of defects, which could slow the oxygen diffusion in the composites. The high thermal conductivity could transfer the heat quickly in ablation process, which reduced the heat accumulation on the ablation surface and weakened the thermal erosion. Therefore, the gradient composites possessed an outstanding anti-ablation property at two heat fluxes. Compared with the uniformed distribution composites, the linear and mass ablation rates of the gradient composites decreased by 60.9% and 66.7% at heat flux of 2.38 MW/m² and decreased by 55.9% and 67.2% at heat flux of 4.18 MW/m². Because of the gradient distribution, porous ZrO₂ coating, ZrO₂SiO₂ coating and SiO₂ coating with SiO₂ nanowires were generated on the ablation center, ablation transition zone and ablation edge, respectively. These coatings isolated the sample surface from the flame and inhibited the transport of oxygen into the sample inner.     

Influences of deposition temperature,gas flow rate and ZrC content on the microstructure and anti-ablation performance of CVD-HfC-ZrC coating

To amend the oxidation and ablation resistance of C/C composites, HfC-ZrC biphase coating was synthesized by CVD. Influences of deposition temperature and CH₄ flow rate on the deposition rate, phase constitution and microstructure of the HfC-ZrC coating were investigated. Ablation behavior and ablation mechanism of the HfC-ZrC coating with different ZrC contents were examined. With the deposition temperature rising, the deposition rate and grain size of the HfC-ZrC coating increased. High flow rate of CH₄ was beneficial to improving the deposition rate and reducing the grain size of the HfC-ZrC coating. Moderate ZrC content in the HfC-ZrC coating was conducive to the process of solid solution sintering among HfO₂ and ZrO₂ grains, leading to generating a continuous and compact oxide layer. The coating with HfC/ZrC mole ratio of 1:1 exhibited superior anti-ablation performance, owing to its flat and compact structure and sufficient solid solution sintering among the oxide grains during ablation.     

Microstructure and mechanical performance evolution of C/C–ZrC composites exposed to oxyacetylene flame

C/C–ZrC composites were prepared by isothermal chemical vapor infiltration (ICVI) combined with reactive melt infiltration (RMI). The ablation behavior of the C/C–ZrC was investigated using an oxyacetylene flame. The effect of ablation time on the microstructure and mechanical property evolution of the composite was studied. The results showed that as the ablation time prolonged, the linear and mass ablation rates of the composite increased firstly and then stabilized. After 15 s ablation, the flexural strength and modulus of the C/C–ZrC were interestingly increased by 141.8% and 40.9%, which reached 138.42 MPa and 6.45 GPa, respectively. During ablation, the preferential oxidation effect of ZrC could mitigate the oxidation of pyrolytic carbon (PyC) and carbon fibers, and the volume change induced by the ZrC →ZrO₂ phase transformation could weaken its bonding with PyC, which was beneficial for releasing the internal residual stresses of the C/C–ZrC and then contributed to the mechanical performance improvement.     

Morphology and anti-ablation properties of composites nozzles under the Ф100mm H2O2- polyethylene hybrid rocket motor test

Environmentally friendly commercial applications spurred us to screen a suitable ablative throat material for the hybrid rocket, while preserving its cost-effective advantages as a special chemical motor. In this research, two types of carbon fiber reinforced composites, i.e. carbon/carbon (C/C) composite and C_f/C–SiC–ZrC composite utilized in high temperature environment, were employed to make the hybrid rocket nozzle. By comparison with the high-density graphite, the anti-ablation properties under the firing environment of Ф100mm H₂O₂-polyethylene hybrid rocket motor were characterized. We used whole felt preform to make C/C composite, whose matrix carbon was coming from chemical vapor infiltration of propylene; and the C_f/C–SiC–ZrC composite, which employs the same whole felt preform to make the low-density C/C billet, by infiltrated with Si and Zr organic precursors and pyrolysis at elevated temperatures repeatedly to make the advanced ceramic matrix composite. The firing test lasted 40s for all the candidate materials and the result indicated that the C_f/C–SiC–ZrC composite, whose average linear ablation rate was only 0.003 mm/s, was the most stable one in the firing environment. The SEM images gave detailed morphologies of those nozzle throat materials and proved that the fiber architecture, together with the glassy ceramic oxide, helped the nozzle to withstand the hybrid motor firing environment.