C-SiC Composites Research Articles

Ablation mechanism of Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC composite during plasma ablation above 2000 °C

Air plasma ablation behavior of Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC composite was studied systematically with the surface temperature above 2000 °C at the ablation center. It presents a linear recession rate of 0.15 μm/s and a mass recession rate of 2.05 mg/s after ablation at 4 MW/m2 (2000 °C) for 300 s. Associated with the temperature gradient of the ablation surface, the oxidation products at different locations mainly consist of (TiZrHfNbTa)Ox, (ZrxHf1–x)6(NbyTa1–y)2O17, Ti(NbxTa1–x)2O7, (HfxZr1–x)SiO4, and SiO2. Due to the synergistic effect of the multi-component oxides, oxidation products form a protective structure composed of high melting point oxide skeleton filled with relatively low melting point phases. It retards oxygen inward diffusion and prevents the composite fragmentation caused by plasma mechanical scouring. It is believed that the results would be helpful for further improving the ablation resistance by component design of high entropy ceramics and their composites.

The synthesis of high sinterability (Zr, Hf)C and SiC hybrid nanocrystalline particles by sol-gel method

Multi-phase UHTCs are favoured for their superior ablation resistance and mechanical properties. In this work, to improve the efficiency and decrease the sintering temperature and pressure, the (Zr, Hf)C and SiC hybrid nanocrystalline particles were prepared via the sol-gel method combining carbothermal reduction at 1600 °C. Utilizing their high sinterability, a relative density of 96.1% (Zr, Hf) C–SiC composite was obtained at the conditions of 1900 °C and 30 MPa using SPS technology. XPS and FT-IR results demonstrate that Zr, Hf, and Si were successfully trapped in the cross-linking structure of the precursors. Precursors of Zr, Hf, and Si reached a molecular-level mixture in the gel phase. SEM, XPS, and XRD characterization showed that the Si–C bond was formed preferentially, leading to the emergence of SiC whiskers and SiC wrapped (Zr, Hf)C with increasing temperature. And, the (Zr, Hf)C can be easily generated during solid solution reaction. Eventually, a nanoscale mixture of (Zr, Hf)C and SiC particles was successfully obtained at 1600 °C. The hardness and compressive strength of the (Zr, Hf)C–SiC composite were 12.94 GPa and 622 MPa, respectively. Comparing usual sintering processes (over 2000 °C and 35 MPa), the reason for the improved sinterability can be attributed to the high sintering activity of the (Zr, Hf)C and SiC hybrid particles, and the existence of the solid solution and nano-SiC.

Efficient fabrication and properties of 2D Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC high-entropy ceramic matrix composites via slurry infiltration lamination combined with precursor infiltration and pyrolysis

In this work, an efficient processing route was developed to fabricate Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC composites via slurry infiltration lamination (SIL) combined with precursor infiltration and pyrolysis (PIP). The (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C powder was initially synthesized at 1900 °C. Then the 2D Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC composites were obtained via SIL and PIP at temperatures no higher than 1100 °C. The as-fabricated composites show a density of 2.52 g/cm3 and an open porosity of 15.2 vol%, with a bending strength of 255 ± 15 MPa. The 2D Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC composites also present excellent ablation resistance, with the linear and mass recession rates of 0.33 µm/s and 0.60 mg/s after ablation at 2000 °C/300 s. This work provides a route for the efficient fabrication of Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC composites, and also inspires new strategies to develop high-entropy ceramic matrix composites with high performance.

Understanding the oxidation kinetics of (Ti0.8Nb0.2)C and (Ti0.8Nb0.2)C-SiC composite in high-temperature water vapor

(Ti0.8Nb0.2)C exhibits high oxidation resistance in water vapor up to 1300 ºC, with the addition of 10% wt. SiC, even higher oxidation resistance could maintain up to 1500 ºC. The oxidation scales of both (Ti0.8Nb0.2)C and (Ti0.8Nb0.2)C-SiC composite show preferential oxidation and steep, opposite chemical gradients of Ti and Nb, implying that the predominant controlling factor is the outward diffusion of the metal elements by the interstitialcy mechanism. Dense and oriented (Ti1−xNbx)O2 oxidation scale accounts for the high oxidation resistance. A continuous and dense SiO2 layer further improved the oxidation resistance in (Ti0.8Nb0.2)C-SiC composite.

Influence of the SiC matrix introduction time on the microstructure and mechanical properties of Cf/Hf0.5Zr0.5C-SiC ultra-high temperature composites

C f /Hf 0.5 Zr 0.5 C-SiC composites were prepared by introducing Hf 0.5 Zr 0.5 C matrix (11 cycles) and SiC matrix (9 cycles) into the carbon cloth preform through precursor impregnation and pyrolysis (PIP) process. The influence of the introduction time of SiC matrix on the microstructure and mechanical properties of C f /Hf 0.5 Zr 0.5 C-SiC composites was studied, and the results show that with the increase of the PIP cycles of the SiC matrix introduced before Hf 0.5 Zr 0.5 C matrix, the composite open porosity decreased, and the flexural strength and modulus presented an obvious upward trend. CS45 sample, which has 4 cycles of PIP SiC introduced in advance, has the highest flexural strength, flexural modulus and interfacial shear strength of 402.73 ± 35.73 MPa, 56.92 ± 3.97 GPa and 100.88 ± 7.79 MPa, respectively. Hf 0.5 Zr 0.5 C matrix has a loose and porous structure, so when more SiC matrix was introduced in advance, its covering effect on the surface of fibers led to less intra-bundle pores and thusly denser composite structure, and due to the compactness of SiC matrix, better overall bonding of fiber, interface and matrix was achieved, as well as better load transfer effect, which led to obvious interfacial debonding and cracking based on the in-situ SEM observation during flexural tests. While in the sample without pre-introduced SiC, the cracking occurred mainly between the interface and porous matrix and the overall performance of the material was poor.

Fabrication and properties of Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC high-entropy ceramic matrix composites via precursor infiltration and pyrolysis

In this work, Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC high-entropy ceramic matrix composites were reported for the first time. Based on the systematic study of the pyrolysis and solid-solution mechanisms of (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C precursor by Fourier transform infrared spectroscopy, TG-MS and XRD, Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC with uniform phase and element distribution were successfully fabricated by precursor infiltration and pyrolysis. The as-fabricated composites have a density and open porosity of 2.40 g/cm3 and 13.32 vol% respectively, with outstanding bending strength (322 MPa) and fracture toughness (8.24 MPa m1/2). The Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC composites also present excellent ablation resistant property at a heat flux density of 5 MW/m2, with linear and mass recession rates of 2.89 μm/s and 2.60 mg/s respectively. The excellent combinations of mechanical and ablation resistant properties make the Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC composites a new generation of reliable ultra-high temperature materials.

Sol-infiltrated multilayer SiC/yttrium silicate coatings for imparting enhanced oxidation resistance to C-SiC composites

Yttrium silicate coatings are applied on C-SiC composites for advanced aerospace structural applications at high temperatures. The Air Plasma Spray (APS) method is widely used for the deposition of yttrium silicate coatings. However, the oxidation resistance offered by the APS-deposited coating is limited by the inherent porosity and micro-cracks in the coating. The present study demonstrates the effective sealing of the pores and micro-cracks in the APS coating by impregnation with yttrium silicate sol followed by sintering at 1400 °C. The cyclic oxidation behavior is comparatively assessed at 1300 and 1500 °C in air for the C-SiC composite samples applied with multilayer coatings comprising combinations of CVD SiC/APS yttrium silicate/sol infiltrated yttrium silicate coatings. The lone SiC coated and the SiC/APS yttrium silicate coated samples exhibited rapid decrease in weight. On the contrary, the SiC/APS coated samples infiltrated with yttrium silicate sol exhibited significantly improved oxidation resistance. The weight loss during oxidation was prevented after infiltration of the yttrium silicate sol at a higher vacuum level of 1 mbar, which effected in better healing of the pores in the APS coating and formation of a dense yttrium silicate scale on the surface.

Enhanced irradiation resistance and thermal conductivity of SiC induced by the addition of carbon under Au2+ ion irradiation

A significant decrease in the thermal conductivity of SiC after irradiation has hindered its practical applications. To solve this problem, polymer-derived pure SiC and C-SiC composites were irradiated under 4 MeV Au2+ ions, and their thermal conductivity was evaluated. The time-domain thermoreflectance method was found to be effective and sensitive to obtain the thermal conductivity of the irradiated layer. In pure SiC, irradiation-induced complete amorphous SiC significantly decreased the thermal conductivity. However, in C-SiC composites, the heterogeneous interface between C and SiC probably increased the irradiation resistance, leaving residual crystallinity in both C and SiC phases and resulting in a higher thermal conductivity. The thermal conductivity of C-SiC composites was dominated by SiC matrix. The optimal thermal conductivity of SiC related composites after irradiation can be designed by controlling the distribution, size, content, interface, and degree of crystallinity of the two phases in the future.

Micro-structural evolution during diffusion bonding of C-SiC/C-SiC composite using Ti interlayer

Diffusion bonding of C-SiC composite was achieved with Ti interlayer at 1500°C for 3h with the applied pressure of 20MPa. The joined C-SiC composite showed the apparent shear strength of 19MPa and the sample fractured away from the joint. The microstructure of joint consists of Ti3SiC2 MAX phase, TiSi2 and TiC in which Ti3SiC2 was the major phase. The distribution of phases in the microstructure of joint was categorized into three different zones based on electron backscattered diffraction (EBSD) results. The first zone consists of a thin continuous TiSi2 phase, which was followed by a thick zone of Ti3SiC2 MAX phase. In the middle of the sample, a mix phase zone was found. The reaction mechanism was established for the evolution above microstructure of joined C-SiC composite.

Preparation and Microstructure Characterizations of Novel C/C-Zr(Hf)B<sub>2</sub>-Zr(Hf)C-SiC Composites

A series of novel C/C-Zr (Hf)B2-Zr (Hf)C-SiC composites were prepared by chemical vapor infiltration (CVI) of pyrolytic carbon and polymeric impregnation and pyrolysis (PIP) with hybrid polymeric precursors of SiC (polycarbosilane), Zr (Hf)C and Zr (Hf)B2 in carbon fiber preforms. The formed ultra-high temperature ceramics (UHTCs) matrix of SiC-ZrC-ZrB2 and SiC-HfC-HfB2 were designed to improve the oxidation resistance of carbon/carbon composite at very high temperatures above 2000°C. The pyrolysis process of Zr (Hf)C and Zr (Hf)B2 polymeric precursors was investigated, and the results showed that the hybrid precursors could be successfully transformed into Zr (Hf)C and Zr (Hf)B2 ceramic particles with the sizes of nanometer with temperatures above 1500°C. Furthermore, the multiscale structure of C/C-Zr (Hf)B2-Zr (Hf)C-SiC composites were also characterized , showing that the carbon fibers were covered by pyrolytic carbon, and the continuous ceramic matrix was well dispersed, formed by Zr (Hf)C and Zr (Hf)B2 nanoparticles distributing homogeneously in the continuous SiC matrix. This homogeneous dispersion of composite ceramics of Zr (Hf)C and Zr (Hf)B2 with SiC plays excellent protection of C/C composites from oxidation at high temperature via formation of stable oxides coatings.

In situ synthesis of nano size silicon carbide and fabrication of C[sbnd]SiC composites during the siliconization process of mesocarbon microbeads preforms

CSiC composites with carbon-based mesocarbon microbeads (MCMBs) preforms are a new type of high-performance and high-temperature structural materials for aerospace applications. In the present study, MCMB-SiC composites were fabricated by liquid silicon infiltration (LSI). Physical and mechanical properties such as density, porosity and bending strength were measured before and after siliconization. The results show the CSiC composites have excellent bending strength, density and porosity of 210MPa, 2.41g/cm3 and 0.62%, respectively. The chemical analysis shows that the composite is composed of 89% SiC, 2% Si and 9% C. The microstructural results also show the existence of two different areas of SiC, one zone of coarse micron size SiC at SiCSi interface and the other zone consists of fine nano-SiC particles at SiCC interfaces. The formation mechanism governing the siliconization of porous MCMB preform was also investigated.

Mechanical properties of LSI based 3D-stitched-C-SiC composites prepared by coal–tar pitch as carbon precursor

3D-stitched C-SiC composites are fabricated by liquid-silicon-infiltration (LSI) method for thrust-vectoring of a solid propulsion system. Mechanical properties are investigated under bending, tensile, and impact loading at room-temperature. Weibull-modulus approach is applied to analyze bending strength. Weibull-modulus is found to be 10.18 while characteristic strength is 185.7 MPa. Effect of temperature on the bending strength was studied up to 1200 °C in air. Micro-hardness is measured at room temperature.

Life Prediction of 3D Woven C-SiC Composites at High Temperatures with Low-frequency Cyclic Stresses

The corrosion of a C-SiC composite with SiC coating (SiC-C/SiC) is studied under a low-frequency cyclic stress in various gas atmospheres of oxygen, water vapor, and sodium sulfate vapor at temperatures from 1000 to 1300 C. A model for the cyclic stress corrosion mechanism of the composite is proposed from the experimental study. An equation to predict the lifetime of the composite under cyclic stress conditions is derived from the model. It is found that under cyclic stress conditions, oxygen is the only major factor degrading the composite and the corrosion kinetic is controlled by the carbon-oxygen reaction. The validity of the model and the equation is confirmed well by the experimental results.

Oxidation of Boron Carbide-Silicon Carbide Composite at 1073 to 1773 K

The oxidation behavior of B 4 C-(25-60 mol%)SiC composites prepared by arc-melting was investigated in the temperature range of 1073 to 1773K using a thermogravimetric technique. Liquid borosilicate, solid SiO 2 and carbon were identified as oxidation products by X-ray diffraction and Raman spectroscopy. Mass gain was observed during oxidation at 1073 K, while mass loss due to the vaporization of boron oxide in liquid borosilicate was observed at temperatures of 1273 K and higher. In situ Raman spectra of the surface of B 4 C-SiC composites indicated that the silica concentration in the liquid borosilicate increased with increasing SiC content in the composite. Micro-Raman spectroscopy showed that carbon was enriched in the borosilicate layer close to the oxide/composite interface. The parabolic rate constants for B 4 C-50mol%SiC composites at 1073 K were proportional to ambient oxygen partial pressures ranging between 30 and 100kPa. The diffusion of oxygen molecules through the liquid borosilicate layer could be the rate-controlling process. The increase of SiC content in the B 4 C-SiC composites improved the oxidation resistance in both the mass gain and mass loss regions.

Effect of Weave Architecture on Tensile Properties and Local Strain Heterogeneity in Thin‐Sheet C–SiC Composites

Room‐temperature tensile properties were measured for two thin C–SiC composites fabricated from single sheets of carbon fiber fabric with nominally the same weave architecture, but different fiber packing densities. The SiC matrixes were formed by infiltration and pyrolysis of a polymer precursor (allylhydridopolycarbosilane). The tensile properties are related to microstructural characteristics, observed damage mechanisms, and measurements of local strain concentrations by speckle interferometry. Differences are observed between the responses of these thin‐sheet composites and conventional CVI‐matrix composites of larger thickness. Debonding between transverse and longitudinal fiber tows allows significant strains due to straightening of initial wavy fiber tows and leads to local stress concentrations. The strength and elastic modulus are affected by the waviness of the longitudinal tows.

Oxidation-Protection Methodology for Long-Term use of Carbon-Carbon Fiber-Matrix Composites in Oxidizing Ambients

ABSTRACTA methodology is described for protecting Carbon-Carbon fiber-matrix composite (C-C) components from oxidation for extended use in oxidizing ambients for lifetimes of the order of 10,000 hours, from room temperature to 650°C. This time-temperature profile is relevant to applications such as airborne heat exchangers. Weight changes of oxidation-protected, pitch-fiber based C-C coupons in flowing dry air at 650°C are presented. Two types of external protective approaches are compared: (a) multi-phase, borophosphate-based fluidizing overseal coatings applied directly to C-C, and (b) the same overseal coatings applied to CVD SiOxCy coated C-C. The latter, dual-coating approach provides an effective engineering solution for the above temperature-time profile and is particularly applicable to thin (0.1–3 mm thick), complex-shaped articles. The behavior of inert substrates (oxidized silicon) with the same overseal coatings is compared to the behavior of the C-C substrates. This approach can be applied with optional modifications to suit other environmental conditions, and other carbon-containing materials, such as carbon foams and C-SiC composites.

Characterization of Directionally Solidified B<SUB>4</SUB>C-SiC Composites Prepared by a Floating Zone Method

Directionally solidified B 4 C-TiB 2 composites were prepared by a Floating Zone method. TiB 2 phases in a rod shape were continuously connected in the B 4 C matrix. The c-axes of TiB 2 and B 4 C phases were perpendicular and tilted 22° to the growth direction, respectively, The (101) and (120) planes of the B 4 C were in parallel to the (001) and (100) planes of TiB 2 , respectively. The electrical conductivity of the composite parallel to the growth direction (σ || ) was greater than monolithic B 4 C by a factor of 100 to 1000. The thermal conductivity of the composite parallel to the growth direction (κ || ) was about one and a half times as high as that of B 4 C. The anisotropy of electrical and thermal conductivity were basically explained by a mixing law using the values of B 4 C and TiB 2 . The microhardness of the composite was almost the same as that of B 4 C. The electric discharge machining of the composite was possible owing to the enhancement of electrical conductivity.

Tribological behaviour of carbon-fibre-reinforced SiC matrix composites

Reinforcement of monolithic ceramics by carbon fibres improves the tribological behaviour of ceramic materials. The lamellar graphite of carbon fibres can act as a natural third body, leading to low friction. The tribological behaviour of carbon-fibre (M40)-reinforced SiC matrix composites under different experimental conditions (velocity, load and temperature) is discussed in this paper. C-SiC composites are tested in sliding contact using a disc-on-disc tribometer. The results show that the behaviour of the contact is highly dependent on friction conditions. Friction transitions can occur during tests. The purpose of this paper is to identify the mechanisms which lead to these transitions. The main hypothesis concerns the mechanical and thermal fatigue phenomena. Under restrictive experimental conditions the C-SiC composites can be considered as self-lubricating materials. Self-lubricating conditions are experimentally given by a curve according to test temperature and pv parameter.

Process and wear behavior of monolithic SiC and short carbon fiber-SiC matrix composite

The process and wear behavior of monolithic SiC and 10 vol. % short carbon fiber-SiC matrix (C-SiC) composite have been studied. The results indicate that, among ethyl alcohol, acetone, n-hexane and n-octyl alcohol, n-octyl alcohol was the most effective dispersing agent in dispersing both SiC powder and short carbon fiber. Among AlN, Al2O3, B4C, graphite, AlN/B4C, AlN/graphite, B4C/graphite and Al2O3/B4C, the most effective sintering aid for the fabrication of SiC and C-SiC composite was a mixture of 2 wt% AlN and 0.5 wt% graphite. The monolithic SiC hot-pressed at 2100°C exhibited higher density but lower flexural strength than those hot-pressed at 2000°C due to a grain growth effect. For the C-SiC composite, both density and strength of the composite hot-pressed at 2100°C were generally higher than those hot-pressed at 2000°C. The density and strength of C-SiC composite were lower than those of monolithic SiC under the same hot pressing conditions due to a higher porosity level in the composite. When monolithic SiC slid against C-SiC composite, the weight losses of SiC and the composite were each less than that of self-mated SiC or self-mated C-SiC. In the self-mated SiC tribosystem, a mechanically stable film could not be established, resulting in an essentially constant wear rate. When sliding against C-SiC, a thin, smooth and adherent debris film was quickly formed on the SiC surface, resulting in a lower wear.

Novel, Matched CTE Integrated Substrates for Power Electronics

ABSTRACTRapid advances in high power electronic packaging require the development of new heat-sink/substrate materials. Advanced composites designed to provide thermal control as well as improved thermal conductivity have the potential to provide benefits in the removal of excess heat from electronic devices. Carbon-carbon (C-C)composites are under consideration for numerous electronic packaging applications. A new manufacturing process has been developed to produce high thermal conductivity (400 W/mK) C-C composites at greatly reduced cost (less than $50/lb). However, low CTE (0.25 × 10−6cm/cm °C) of C-C composites results in reduced fatigue life in chipon- board (COB) applications with silicon chips (CTE ≈ 2.6 × 10−6 cm/cm °C). A novel process was developed to convert the carbon matrix into the SiC matrix which retains the overall high composite thermal conductivity. This novel technology is well-suited for COB applications. Several types of coatings, such as CVD AIN, CVD Si and a polymer slurry-based low dielectric coating were applied to the C-SiC composite. Processing schemes were developed to produce crack-free coatings. Metallization of the dielectric coating was performed for the process integration with electronic devices. Thus, integrated substrates for power electronics were fabricated without the need of conventional metal/ceramic joining and associated high stresses. The properties of this new composite material for power electronics substrates are presented.