Oxidation analysis of 2D C/ZrC–SiC composites with different coating structures in CH4 combustion gas environment

2D C/ZrC–SiC composites were fabricated by chemical vapor infiltration combined with polymer slurry infiltration and pyrolysis. Liquid highly branched polycarbosilane was used as the pre-ceramic precursor. In order to improve the oxidation resistance, three kinds of coating structures were prepared on C/ZrC–SiC composites: pure zirconium carbide coating, SiC–ZrC coating, and ZrB₂–SiC coating. Structural evolutions of the as-produced composites after oxidation in CH₄ combustion gas atmosphere at about 1800 °C were investigated and compared. Based on a model of the oxidation process, the mixture ZrB₂–CVD SiC showed the best oxidation resistance.     

Mechanical and dielectric properties of SiCf/BN/SiBCN composites via different synthesis technologies

SiC fibers reinforced SiBCN ceramic matrix composites (SiC_f/BN/SiBCN composites) were synthesized by direct chemical vapor infiltration (CVI), polymer infiltration pyrolysis (PIP) or chemical vapor infiltration combined with polymer infiltration pyrolysis (CVI + PIP). It is shown that the insertion of a continuous and dense SiBCN matrix via the CVI process improves the flexural strength and modulus. Interface debonding and fiber pullout happened with 50–100 nm BN interface in CVI and CVI + PIP SiC_f/BN/SiBCN composites. The relative complex permittivity was measured in X-band. Higher ε′′ values in CVI-containing composites can be observed, which can be attributed to the accumulation of C and SiC phases and a multilayer matrix. Strong electromagnetic wave attenuation ability was obtained with high dielectric loss.     

Oxidation behavior of C/SiC-SiBCN composites at high temperature

In order to improve the anti-oxidation performance of C/SiC composites at high temperature, C/SiC composites should be modified by self-healing components. SiBCN ceramic is an ideal self-healing component because of excellent oxidation resistance and thermal stability. C/SiC composites were modified by PDC SiBCN ceramic (C/SiC-SiBCN) by using CVI combined with polymer infiltration and on-line pyrolysis (PI-OP). The oxidation behaviors of C/SiC composites fabricated by CVI method and C/SiC-SiBCN composites fabricated by CVI + PI-OP method and CVI + PIP method at different temperatures in air were compared. The results showed that the strength retention ratios of the composites fabricated by the three methods decreased with the increase of temperature. Compared with the samples fabricated by the other two methods, the weight loss of the samples fabricated by CVI + PI-OP method was greater, but the strength retention ratio was higher.     

Mechanical properties and microstructures of Cf/SiC-ZrC composites using T700SC carbon fibers as reinforcements

C_f/SiC-ZrC composites were fabricated through mold-pressing and polymer infiltration and pyrolysis (PIP) process using T700SC carbon fibers as reinforcements. The effects of interphases on the mechanical properties and microstructures of composites were studied. Composite showed brittle fracture behavior and low bending stress of 81 ± 24 MPa when no interphase was deposited on the fiber surface. With the deposition of a PyC/SiC interphase, composite showed typical non-brittle fracture behavior and the bending stress increased to 401 ± 64 MPa and a large amount of pulled-out fibers could be observed on the fracture surface. Meanwhile, it could also be concluded from the microstructures of the composites that the existed interphases had a great hindering effect on the infiltration of ZrC into the intra-bundle zones in the slurry infiltration process. The TEM analysis results showed that the carbon fibers were almost not eroded and the brittle fracture behavior may be mainly ascribed to the strong bonding between fibers and matrix.     

Polymer-metal slurry reactive melt infiltration: A flexible and controllable ceramic modification strategy for irregular C/C components

Herein, we investigate the applicability of the polycarbosilane (PCS)–metal slurry reactive melt infiltration (RMI) process to various metals. The slurry exhibiting the best ceramized ability was used to examine the relationship between the ceramic thickness and reactive time, ceramic thickness and reactive temperature, and infiltration depth and slurry-coating thickness. The results show that the thickness of the ceramic layer increases with reactive time and temperature and the infiltration depth increases with the coating thickness. PCS–Si₉₀Zr₁₀ slurry RMI was selected to modify cylindrical nozzle C/C preforms, and dense C/C–SiC–ZrC composites with a density of ~2.05 g cm⁻³ were obtained. Owing to the good control of the PCS–Si₉₀Zr₁₀ slurry RMI on the interface, matrix, and carbon fiber of the as-received cylindrical composites, the bending strength of the C/C–SiC–ZrC composites was as high as 306.4 MPa, which is considerably higher than that of a C/C preforms (70.4 MPa). Considering the ablation resistance, the mass and linear ablation rates of the C/C–SiC–ZrC composite (~0.29 mg s⁻¹ and ~2.48 × 10⁻³ mm s⁻¹, respectively) were similar to those of the composites prepared using traditional RMI (~0.23 mg s⁻¹ and ~2.29 × 10⁻³ mm s⁻¹). The proposed polymer–metal RMI is more suitable for the modification of C/C preforms with thin-wall structures owing to its advantages including precise control of infiltration dose and flexible operation of slurry coating. Furthermore, it is suitable for the local modification of C/C components.     

Fabrication and microstructure of 3D Cf /ZrC-SiC composites: through RMI method with ZrO2 powders as pore-making agent

3D C_f/ZrC–SiC composites were prepared by a combination process of slurry infiltration and reactive melt infiltration. ZrO₂ powders and ZrSi₂ alloy, both of which reacted with amorphous carbon, were used as pore-making agent and infiltrator, respectively. After carbothermal reduction at 1650 °C, X-ray diffraction analysis revealed that ZrO₂ powders were completely converted into ZrC by reacting with amorphous carbon, and an in-situ formed submicron porous configuration was observed at the areas containing ZrO₂. Results showed that the matrix in composites mainly consisted of SiC, ZrC and a small quantity of residual metal. SEM and TEM images revealed the formation of ZrC or SiC intergranular particles in the matrix and the characteristic around the residual resin carbon. The composites had a bending strength of 94.89±16.7 MPa, fracture toughness of 11.0±0.98 MPa m^1/2, bulk density of 3.36±0.01 g/cm³, and open porosity of 4.64±0.40%. The formation mechanisms of ZrC–SiC dual matrix and intrabundles׳ structure were discussed in the article.     

Mechanical behaviour and microstructure of Cf/ZrC,Cf/SiC and Cf/ZrC – SiC composites

Cf/ZrC, Cf/SiC and Cf/ZrC–SiC composites were successfully prepared by polymer infiltration and pyrolysis (PIP) using polycarbosilane and a liquid ZrC precursor. The densification process, mechanical properties and microstructures were studied in a view of comparison. After the same total 20 PIP cycles, the Cf/ZrC, Cf/SiC and Cf/ZrC–SiC composites had flexural strengths of 50.1±5.3, 285.7±22.6, 141.5±13.1?MPa respectively; elastic moduli of 7.8±0.9, 57.1±3.2 and 45.1±2.6?GPa respectively; and fracture toughness of 2.5±0.2, 10.4±0.9 and 10.9±1.1?MPa m^1/2 respectively. With the introduction of high modulus SiC phase into the ZrC matrix, the densification and modulus of the matrix were improved; as a result, the Cf/ZrC–SiC composite showed higher mechanical properties compared to Cf/ZrC.     

Ablation mechanism of C/C–SiC and C/C–SiC–ZrC composites in hypersonic oxygen-enriched environment

In this study, C/C–SiC and C/C–SiC–ZrC composites were prepared via chemical vapor infiltration and polymer infiltration pyrolysis, and the ablation mechanism under hypersonic oxygen-rich environmental conditions was investigated. The C/C–SiC composites demonstrate an excellent ablation resistance in a hypersonic oxygen-rich environment with a relatively low temperature and speed of approximately 1800 K and 1100 m/s, respectively. It is only in the ablation center area with higher temperatures that a certain degree of thermochemical ablation was observed. The mass and linear ablation rates of C/C–SiC composites (0.027 g/s and 0.117 mm/s, respectively) showed a significant increase in a hypersonic oxygen-rich environment with a temperature and velocity of approximately 2050 K and 2000 m/s, respectively. The high-temperature ablation resistance of ZrC-modified C/C–SiC–ZrC composites improved significantly. However, the ZrC ceramic component had a considerable impact on the ablation resistance of the material. The structural integrity of C/C–20SiC–30ZrC composites was relatively high in hypersonic oxygen-rich environments with a jet temperature and velocity of 2050 K and 2000 m/s, respectively, and mass and linear ablation rates were 0.012 g/s and 0.015 mm/s, respectively. When the ZrC content increased by 40%, the ablation resistance of the composite reduced significantly, whereas the mass and linear ablation rates increased to 0.043 g/s and 0.130 mm/s, respectively.     

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.     

Preparation and properties of 2D C/SiC-ZrB2-TaC composites

Two-dimensional (2D) C/SiC-ZrB₂-TaC composites were fabricated by chemical vapor infiltration (CVI) combined with slurry paste (SP) method. 2D laminate was prepared by stacking carbon cloth that was pasted with a mixture of polycarbosilane-ZrB₂-TaC slurry. A small amount of carbon fiber tows were introduced into the preform in the vertical direction. After heat-treated at 1800 °C, the 2D laminate was densified with SiC by CVI to obtain 2D C/SiC-ZrB₂-TaC composites. Properties including flexural strength, interlaminar shear strength, and thermal expansion of the composites were investigated. The ablation test was carried out under an oxyacetylene torch flame. The morphologies of the ablated specimens were analyzed. The results indicate that the adding vertical fiber tows and heat-treatment at 1800 °C can greatly improve the mechanical properties of the composites. The co-addition of TaC and ZrB₂ powders into C/SiC composite effectively enhance its ablation resistance.     

Fabrication of Cf/ZrC–SiC composites using Zr–8.8Si alloy by melt infiltration

Cf/ZrC–SiC composites were fabricated by melt infiltration at 1800 °C using Zr–8.8Si alloy and carbon felt preforms. Microstructural analysis showed the formation of both ZrC and SiC phases in the matrix, in which ZrC acted as a main composition of the resulting composites. The results showed that carbon matrix reacted preferentially with Si of Zr–8.8Si alloy, which caused the formation of SiC first and then ZrC. The designed carbon coating by pyrolysis prevented the severe reaction between fibers and the melt. The composites could be more dense and uniform with the bending strength of 53.3 MPa, when preforms had a high open porosity (47.2%) with small size pores (10–40 μm).     

Friction and wear properties of C/C–SiC braking composites

Two series of C/C–SiC composites were fabricated via precursor infiltration pyrolysis (PIP) and chemical vapor infiltration (CVI) using porous C/C composites with different original densities as preforms, respectively. The tribological characteristics of C/C–SiC braking composites were investigated by means of MM-1000 type of friction testing machine. The friction and wear behaviors of the two series of composites were compared and the factors that influence the friction and wear properties of C/C–SiC composites were discussed. Results show that the friction and wear properties relate close-knit to the content of SiC and porosity. As the original preform density increasing, the content of SiC and porosity decrease, and then the friction coefficient increases obviously, the braking time and the wear rate both decrease. Preparation techniques play an important role in the tribological properties of C/C–SiC composites. Compared with PIP process, the samples from CVI have a little higher friction coefficient, shorter braking time and higher wear rate.     

Morphology and anti-ablation properties of PIP Cf/C–SiC composites with different CVI carbon content under 4.2 MW/m2 heat flux oxy-acetylene test

In this work, the needled carbon fiber preforms were used to make seven groups of carbon/carbon composite billets with different matrix carbon contents by controlling the processing time of chemical vapor infiltration (CVI). C_f/C–SiC composites were prepared by infiltration of SiC into these C/C composites billets using polycarbosilane (PCS) through precursor infiltration and pyrolysis (PIP). After oxy-acetylene torch testing (heat flux of 4.2 MW/m²) for 200s, 300s and 400s, respectively, it revealed that the anti-ablation properties of the C_f/C–SiC composite samples were enhanced by a higher content of SiC matrix. Additionally, specimens bearing longer duration tests showed a trend of lower average ablation rates. The lowest linear ablation rate is 0.008 mm/s and the mass ablation rate is 0.0019 g/s for those high SiC content samples tested for 400s. The SEM images of the tested samples showed the mechanism and the non-linear process of ablation resistance progression.     

Oxidation behavior of oxidation protective coatings for PIP-C/SiC composites at 1500 °C

Three-dimensional carbon fiber reinforced silicon carbide (C/SiC) composites were fabricated by precursor infiltration and pyrolysis (PIP) with polycarbosilane as the matrix precursor, SiC coating prepared by chemical vapor deposition (CVD) and ZrB₂-SiC/SiC coating prepared by CVD with slurry painting were applied on C/SiC composites, respectively. The oxidation of three samples at 1500 °C was compared and their microstructures and mechanical properties were investigated. The results show that the C/SiC without coating is distorted quickly. The mass loss of SiC coating coated sample is 4.6% after 2 h oxidation and the sample with ZrB₂-SiC/SiC multilayer coating only has 0.4% mass loss even after oxidation. ZrB₂-SiC/SiC multilayer coating can provide longtime protection for C/SiC composites. The mode of the fracture behavior of C/SiC composites was also changed. When with coating, the fracture mode of C/SiC composites became brittle. When after oxidation, the fracture mode of C/SiC composites without and with coating also became brittle.     

Microstructure and tribological properties of PIP-SiC modified C/C–SiC brake materials

A combination method of precursor infiltration and pyrolysis (PIP), chemical vapor infiltration (CVI) and liquid silicon infiltration (LSI) was proposed to prepare PIP-SiC modified C/C–SiC brake materials. The SiC ceramic matrix pyrolyzed by polymethysilane (PMS) homogeneously dispersed in the fiber bundles region, which improved the plough resistance of local C/C region and the wear resistance of C/C–SiC brake materials. When the braking speed rises to 28 m/s, the fluctuation range of friction coefficient was limited to 0.026. The linear wear rate of the as-prepared composites was could be ~50% less than that of C/C–SiC, when the braking speed was above 15 m/s (for instance, the wear rate of 1.02 μm/(side·cycle) at 28 m/s less than 2.02 μm/(side·cycle) of traditional C/C– SiC). The fading ratio D of CoF under wet conditions was ~11%. The results showed that introducing PIP-SiC could stabilize the braking process and effectively prolong the service life of C/C–SiC brake materials.     

Manufacturing 2D carbon-fiber-reinforced SiC matrix composites by slurry infiltration and PIP process

Sub-micrometer SiC particles were firstly added to the preceramic solution in the first infiltration step to enhance the mechanical properties of 2D C_f/SiC composites fabricated via polymer infiltration and pyrolysis (PIP) process. The effects of pyrolysis temperature and SiC-filler content on microstructures and properties of the composites were systematically studied. The results show that the failure stress and fracture toughness increased with the increase of pyrolysis temperature. SiC filler of sub-micron scale infiltrated into the composites increased the mechanical properties. As a result, for the finally fabricated composite infiltrated with a slurry containing 40 wt.% SiC filler, the failure stress was doubled compared to that without SiC filler addition, and the fracture toughness reached ≈10 MPa m^1/2.     

Preparation and ablation properties of SiC nanowire-reinforced ZrC–SiC coating-matrix integrated C/C composites

A modification of the precursor infiltration pyrolysis (PIP) method was explored to prepare the integrated doped ceramic matrix and coating by the added SiC nanowires layer and shape-stabilization process. The epitaxial layer of SiC nanowires provided surficial attachments for the precursor. And the shape-stabilization process aggregated loose ceramic particles into a coating. Then the SiC nanowire-reinforced ZrC–SiC coating-matrix integrated C/C (S/SZ-CZ/C) composite was simply prepared by the modified PIP method. The bonding strength between the coating and matrix of the S/SZ-CZ/C composite was improved. Through the ablation test, the mass and linear ablation rate of the S/SZ-CZ/C composite were 0.46 mg/s and 0.67 μm/s, which were 60.34 % and 74.91 % lower than those of the SiC nanowire-reinforced C/C–ZrC (S/CZ/C) composite, respectively. The integration of the coating and matrix enabled the formation of a continuous oxide layer of molten SiO₂ and ZrO₂ in the ablation process, which helped to block the oxygen and heat during the ablation test. Thus the ablation resistance of the materials was systematically and effectively improved.     

Effect of ZrC content on the properties of biomorphic C–ZrC–SiC composites prepared using hybrid precursors of novel organometallic zirconium polymer and polycarbosilane

A novel organometallic zirconium polymer was synthesized through the copolycondensation using n-butyllithium, 1,4-diethynylbenzene, phenylacetylene and zirconium tetrachloride as raw materials. Then biomorphic C–ZrC–SiC composites were fabricated from corn stover templates by precursor infiltration and pyrolysis process using hybrid polymeric precursors containing the organometallic zirconium polymer and polycarbosilane. The microstructure, mechanical properties and oxidation resistance of the composites were investigated. With ZrC content increasing, the mechanical properties of the composites were enhanced due to dispersion strengthening and grain fining of the homogeneously dispersed ZrC nanoparticles. The oxidation behavior of C–SiC–ZrC indicated that the oxidation resistance of the composite was reduced at 1000 °C but improved at 1500 °C with the increase of ZrC content. The improved oxidation resistance was mainly attributed to a proper ZrC content, the formation of ZrSiO₄ layer on the surface of the composite, and its matrix microstructure characterized by a nano-sized dispersion of ZrC–SiC phases.     

Effects of fabrication processes on the properties of SiC/SiC composites

Precursor infiltration and pyrolysis (PIP) and chemical vapor infiltration (CVI) were used to fabricate SiC/SiC composites on a four-step 3D SiC fibre preform deposited with a pyrolytic carbon interface. The effects of fabrication processes on the microstructure and mechanical properties of the SiC/SiC composites were studied. Results showed the presence of irregular cracks in the matrix of the SiC/SiC composites prepared through PIP, and the crystal structure was amorphous. The room temperature flexural strength and modulus were 873.62 MPa and 98.16 GPa, respectively. The matrix of the SiC/SiC composites prepared through CVI was tightly bonded without cracks, the crystal structure had high crystallinity, and the room temperature bending strength and modulus were 790.79 MPa and 150.32 GPa, respectively. After heat treatment at 1300 °C for 50 h, the flexural strength and modulus retention rate of the SiC/SiC composites prepared through PIP were 50.01% and 61.87%, and those of the composites prepared through CVI were 99.24% and 96.18%, respectively. The mechanism of the evolution of the mechanical properties after heat treatment was examined, and the analysis revealed that it was caused by the different fabrication processes of the SiC matrix. After heat treatment, the SiC crystallites prepared through PIP greatly increased, and the SiOxCy in the matrix decomposed to produce volatile gases SiO and/or CO, ultimately leading to an increase in the number of cracks and porosity in the material and a decrease in the material load-bearing capacity. However, the size of the SiC crystallites prepared through CVI hardly changed, the SiC matrix was tightly bonded without cracks, and the load-bearing capacity only slightly changed.     

Effect of heat treatment on the mechanical properties of PIP–SiC/SiC composites fabricated with a consolidation process

Continuous SiC fiber reinforced SiC matrix composites (SiC/SiC) have been considered as candidates for heat resistant and nuclear materials. Three-dimensional (3D) SiC/SiC composites were fabricated by the polymer impregnation and pyrolysis (PIP) method with a consolidation process, mechanical properties of the composites were found to be significantly improved by the consolidation process. The SiC/SiC composites were then heat treated at 1400 °C, 1600 °C and 1800 °C in an inert atmosphere for 1 h, respectively. The effect of heat treatment temperature on the mechanical properties of the composites was investigated, the mechanical properties of the SiC/SiC composites were improved after heat treatment at 1400 °C, and conversely decreased with increased heat treatment temperature. Furthermore, the effect of heat treatment duration on the properties of the SiC/SiC composites was studied, the composites exhibited excellent thermal stability after heat treatment at 1400 °C within 3 h.