Chemical Vapor Infiltration Method Research Articles

High-temperature mechanical properties and microstructure of 2.5D C/C–SiC composites applied for the brake disc of high-speed train

This paper uses chemical vapor infiltration method to prepare 2.5D C/C-SiC composites, and conducts various tests to reveal its high-temperature mechanical properties and failure mechanism. The results show that the test temperature significantly affects the mechanical properties. As the test temperature increased from room temperature to 800 °C, the tensile strength of the 2.5D C/C-SiC composite dropped from 127.67 ± 20.87 MPa to 94.74 ± 28.15 MPa, and the performance dropped by 25.79 %. The compressive strength dropped from 326.92±17.37 MPa to 192.31 ± 29.15 MPa, resulting in a performance decrease of 41.18 %. The bending strength dropped from 355.74 ± 40.80 MPa to 235.88 ± 23.52 MPa, and the performance dropped by 33.69 %; the interlaminar shear strength dropped from 9.77 ± 2.79 MPa to 7.80 ± 3.26 MPa, and the performance dropped by 20.16 %. High-temperature oxidation will lead to interface degradation, destroy the composite matrix and carbon fiber structure, change the interface bonding strength, and ultimately lead to a decline in composite performance.

Oxygen permeation mass transfer modeling and onion-like micromechanical modeling to predict the effect of multilayered interface on oxidation resistance and mechanical properties of composites

To predict oxidative damage of interfaces and fibers under high temperature aerobic environment and mechanical strength of composites before and after oxidation, oxygen permeation mass transfer modeling and onion-like micromechanical modeling of multilayered interface were proposed. The oxygen mass transfer theory and oxidation damage theory of PyC interface were used to establish the two models. The oxidative damage of PyC interface was extended to (PyC-SiC)n multilayered interface, and transformation of SiC phase and microcracks caused by thermal mismatch were also considered. The law of oxygen permeation mass transfer and the evolution of fiber oxidative damage in the “Carbon fiber/(PyC-SiC)n multilayered interface” region were revealed. The mechanical strength of composites under different interface layers was researched, resembling an onion-like wrapping in layers from the core outwards. Furthermore, Cf@(PyC-SiC)n/SiC(n = 1/2/3/4) composites were prepared by chemical vapor infiltration (CVI) method. The mechanical properties of the composites were tested before and after oxidation. A comparison was made between the experimental and predicted tensile strengths before and after oxidation. The predicted results of tensile strength were found to be in good agreement with the experimental ones. In addition, the results show that PyC-SiC multilayered interface has a positive effect on the tensile strength of the composites, mainly as the cracks are deflected and branched by the multilayered interface to promote the multistage pull-out of the fibers. With the increase of interface number, the oxygen diffusion path was lengthened and zigzagged, reducing the oxidative damage of fiber and interface.

Regulating synergistic micro-nano pore structure of CNT sponge to control EMI shielding performance

The aggregation in high-content carbon nanotube reinforced silica carbide composites (CNT/SiC) imposed constraints for further large-scale industrial applications. This study established a synergistic micro-nano pore structure by assembling CNT bundles to fabricate the CNT sponge preform, and then the SiC matrix was in-situ deposited by chemical vapor infiltration method, which facilitates composites with high density and exceptional properties. The pore size distribution and pore area can be regulated by simply adjusting the compression ratios (CRs) of the as-assembled CNT sponge. Samples with CR of 50 % exhibited noteworthy densification, significantly reduced porosity, and a remarkable 163.54 % extra increase in compression strength compared to uncompressed ones. Additionally, the CNT/SiC composites displayed excellent oxidation resistance and demonstrated improved electromagnetic interference (EMI) shielding performance, which exhibited a substantial increase with higher CRs. These findings underscore the significance of employing appropriate multi-level porosity in CNT preforms to fabricate advanced ceramic matrix composites with superior EMI shielding capabilities.

The oxide-layer configuration alteration and pseudo-ductile crack propagation mechanisms in composites induced by different relative thicknesses of CVI HfC-SiC multiphase matrix

Carbon fiber-reinforced HfC-SiC ceramic matrix composites (Cf/HfC-SiC) with different HfC-SiC matrix thicknesses were prepared by the chemical vapor infiltration method. The microstructure, ablation, and pseudo-ductile fracture behaviors of the composites were studied. The results proved that with the change of the HfC-SiC layer relative thickness, the oxide-layer configuration changed to promote its densification, which improved the ablative protection and mechanical properties of Cf/HfC-SiC composites. After ablation, when the relative volume proportion of the HfC-SiC matrix was the utmost (24.7/15.5), the composites had the best ablation resistance due to the tubular lamination configuration HfO2 layer. This caused the composite to have the highest residual bending strength (215.8 MPa) and strength retention rate (79.7%). In addition, a pseudo-ductile crack propagation model was established to determine the influence of the induction of residual stress and the relative HfC-SiC layer thickness on the fracture behavior in the composites. Results suggested that in the real crack deflection mechanism, due to the induction of residual stress, the stress state in the HfC-SiC matrix with the increase of the HfC layer thickness changed to form more ring deflection cracks at the HfC/SiC interface. It provides a way to study the pseudo-ductility behavior of multiphase matrix composites and explain the improvement of its predictability and failure.

Design of domain-limited CVI reactor for L-shaped C/C structure

New complex-shaped and thin-walled carbon/carbon (C/C) composites have become the main hot structural material for new hypersonic vehicles because of their superior properties. In the preparation of complex-shaped and thin-walled C/C composites by chemical vapor infiltration (CVI) method, problems such as slow density growth and inhomogeneity of density distribution have been hindering the development of C/C hot structure, in order to solve which, this paper proposes a design method for domain-limited CVI reactors for complex-shaped and thin-walled C/C structure, as well as conducts CVI experiments with the designed domain-limited reactor for a L-shaped and thin-walled C/C structure. A coupled multi-physical field model considering flow, diffusion, and chemical reactions was established, which was verified by comparison with experiments. The effects of diameter of hole, distance of neighboring holes, depth of hole and length of reactor on deposition quality were analyzed by simulation. The results showed that larger diameter of hole and smaller distance of neighboring holes would be more favorable for the accumulation of density of structure and depth of hole has little effect on deposition. The best solution is diameter of hole with 18 mm and distance of neighboring holes with 20 mm. Homogeneity of density can be improved by adjusting the specific length of the reactor. For the fabric sizes given in the study, when the specific length of the preform is 3.4, the deposition rate and homogeneity can reach a good level at the same time. This study is a guideline for optimization the quality of C/C structure during processing.

XCT damage evaluation and analysis of SiC/SiC turbine guide vanes after thermal shocks

AbstractIn this paper, the two‐dimensional (2D) (0°/90°) plain‐woven Amosic‐3 SiC/SiC turbine guide vane (TGV) was fabricated using the chemical vapor infiltration method. Thermal and stress analysis of the TGV was conducted using the finite element method analysis. Multiple thermal shock tests at T = 1250, 1350, 1400, 1420, 1450, 1470, and 1480°C were conducted for N = 100, 100, 400, 300, 200, 200, and 700 cycles. After thermal shock tests, the surface damage of the TGV was observed visually, and the micro damage mechanism was analyzed using the scanning electronic microscopy. Micro X‐ray computed tomography was adopted to characterize the internal damages in the SiC/SiC guide vanes. The delamination occurred at the positions approaching internal hollow, due to the weak binding force along the thickness direction and the high thermal shock stress caused by the temperature change. The diameter, area, volume, and sphericity distributions of the pores inside of the guide vanes were also obtained.

Tensile creep properties and damage mechanisms of 2D‐woven C/HfC–SiC composites in high temperature

Tensile creep properties and damage mechanisms of 2D‐woven C/HfC–SiC composites in high temperature

Fabrication of novel multilayer core-shell structured nanofibers network reinforced carbon matrix composites for bone tissue engineering

To further optimize the structure of bone tissue engineering composites, silicon nitride nanowires-pyrolytic carbon-hydroxyapatite-carbon matrix (Si3N4nws@PyCnls-HA-C) composites with multilayer core–shell structures are synthesized by chemical vapor deposition (CVD), pulsed electrodeposition (PED), and chemical vapor infiltration (CVI) methods. The microstructure, in-vitro bioactivity, and in-vivo histocompatibility of Si3N4nws@PyCnls-HA-C (SPHC) composites are evaluated. In-vitro, the SPHC exhibited a cell proliferation rate of 157.7% and demonstrated outstanding protein adsorption. In-vivo, the SPHC demonstrated excellent histocompatibility. Therefore, the SPHC composites can serve as an alternative suitable biomaterial for bone tissue engineering.

In-situ preparation, modulation and mechanism of refractory metal carbide gradient coating

TiC, ZrC and TaC modified layers were in-situ prepared on graphite matrix by chemical vapor infiltration method with metal salts as the activator. Taking the TiC modified layer as an example, through thermodynamic calculation and experiment, the thermal decomposition process of raw materials (Ti/K2TiF6) was analyzed, the formation mechanism of TiC was determined, and the distribution of TiC modified layer was modulated. The results show that activator K2TiF6 has higher decomposition temperature than NH4Cl, which is conducive to improving the utilization rate of raw materials in the gas infiltration process. Increasing the content of Ti powder can increase the concentration of reaction gas and contribute to the formation of TiC modified layer. When the molar ratio of Ti to K2TiF6 is 3:1, the surface thickness and infiltration depth of TiC are 5.42 and 136.24 μm, respectively. Increasing the reaction temperature can improve the rate of in-situ reaction and the thickness of TiC surface layer. When the experimental temperature rises to 1600 °C, the TiC surface layer thickness increases to 20.27 μm.

Effect of carbon fiber preform structures on the mechanical properties of Cf@PyC/SiC composites

Cf@PyC/SiC composites, using needle-punched preforms, 3D orthogonal woven preforms and 3D 4-step braided preforms (braiding angles of 10°, 20° and 30°) as the reinforcement, were obtained through chemical vapor infiltration (CVI) method. The tensile strength before and after oxidation of the composites were investigated, and the microstructure, appearance of fracture and phase component of the composites were also analyzed. The results show that the mechanical properties and oxidation resistance of composites are greatly affected by the preform structures. The tensile strengths of 3D 4-step braided composites with the braiding angle of 10° are the best among all composites before and after oxidation, which are 266.40 ± 16.98 MPa and 238.66 ± 14.98 MPa. Before oxidation, the fibers and matrix at the fracture of 3D 4-step braided composites are in staggered distribution. The mechanical enhancement mechanisms of composites such as crack deflection, interface debonding and fiber pull-out, were beneficial to good performance and excellent mechanical properties. After oxidation, the deflection and branching effects of the interface on the crack are not fully manifested, and enhancement and toughening mechanisms are not fully played due to the oxidation of the carbon fiber and the PyC interface.

Sandwich structure SiCf/Si3N4–SiOC–Si3N4 composites for high-temperature oxidation resistance and microwave absorption

SiC fiber reinforced ceramic matrix composites (SiCf-CMCs) have been widely used as structural-functional materials at high temperatures. However, their mechanical and electromagnetic wave (EMW) absorbing properties will deteriorate due to high-temperature oxidation. Therefore, unique sandwich structure, consisting of inner Si3N4 impedance layer, middle porous SiOC loss layer and dense oxidation-resistant Si3N4 layer, was proposed to enhance multiple material properties in oxidation environment. Herein, SiCf/Si3N4–SiOC–Si3N4 composites was fabricated by alternating chemical vapor infiltration (CVI) and polymer infiltration pyrolysis (PIP) methods. For these composites, SiC fiber is used as both reinforcing phase and electromagnetic (EM) absorber. CVI Si3N4 matrix was distributed in inner and outer layer of the SiCf/Si3N4–SiOC–Si3N4 composites. While inner Si3N4 layer between BN interphase and SiOC matrix forms nano-heterogeneous interphase to consume EM energy and enhance mechanical properties of composites, outer dense and oxidation-resistant CVI Si3N4 coating serves to maintain properties. PIP SiOC matrix exhibits porous structure that can effectively deflect cracks and achieve multiple scattering of EMW. SiCf/Si3N4–SiOC–Si3N4 composites with sandwich structure demonstrated excellent EMW absorbing properties and mechanical performance in high-temperature oxidation environments.

Oxidation behavior and damage mechanism of SiCf/SiC minicomposites with multilayered (BN/SiC)n interfacial coatings at 1200 ℃

ABSTRACT SiCf/SiC minicomposites with multilayered (BN/SiC)n interfacial coatings were fabricated via chemical vapor infiltration and precursor infiltration pyrolysis methods. Oxidation behavior, mechanical properties, and interfacial self-healing mechanism of minicomposites at 1200°C were comparatively studied. In dry air, SiC matrix at edges of composites was oxidized to glassy SiO2, thereby sealing the pores between fibers and matrix, healing microcracks, and preventing the diffusion of oxygen into the material. Results of thermogravimetric–differential thermal analysis proved that glassy borosilicate formed at 910°C and 1050°C in minicomposites with BN/SiC and multilayered (BN/SiC)2 coatings. In water/oxygen atmosphere at 1200°C, there existed an equilibrium between the generation of SiO2 and gaseous Si(OH)4. Uncoated sample and minicomposite with single BN coatings were simultaneously eroded by oxidizing atmosphere in directions perpendicular and parallel to fiber axis. Microholes formed due to BN volatilization were gradually healed by glassy borosilicate in minicomposites containing SiC layers, improving interface self-healing capability of composites. After oxidation in water/oxygen atmosphere for 100 min, minicomposites with multilayered (BN/SiC)2 coatings retained relatively high fracture strength and strain, which were 499.0 MPa and 1.05%, respectively.

The ablation and mechanical behaviors of C/(SiC-ZrC)n multi-layer structure matrix composites by chemical vapor infiltration

Continuous carbon fiber reinforced (SiC-ZrC)n multi-layer structural matrix composites were prepared by isothermal chemical vapor infiltration method. The microstructure, bending and ablation behavior of the composites with different number (n, n = 1, 2, 4) of SiC-ZrC layer were studied. The fracture morphology was step-like fracture. With the increase of n, the number of interfaces doubled, benefiting that the cracks kept deflecting and branching at the interface to consume lots of energy. The bending strength increased from 127.63 MPa (n = 1) to 276.85 MPa (n = 4). After ablation, among the prepared composites, C/(SiC-ZrC)4 composite not only had the highest residual bending strength (169 MPa), but also had the best ablation resistance, which the mass and linear ablation rates were 1.17 ± 0.19 mg/s and 7.50 ± 0.56 µm/s, respectively.

Design, Fabrication, and Mechanical Properties of T-700TM Multiaxial-Warp-Knitting-Needled-C/SiC Composite and Pin.

In this paper, the 12k T-700TM Multiaxial-Warp-Knitting–Needle (MWK–N) C/SiC composite and pin were designed and fabricated using the isothermal chemical vapor infiltration (ICVI) method. The composite’s microstructure and mechanical properties were examined by subjection to tensile and interlaminar shear tests. Three types of double-shear tests were conducted for C/SiC pins, including shear loading perpendicularly, along, and at 45° off-axial to the lamination. The fracture surface of the tensile and shear failure specimens was observed under scanning electronic microscope (SEM). The relationships between the composite’s microstructure, mechanical properties, and damage mechanisms were established. The composite’s average tensile strength was σuts = 68.3 MPa and the average interlaminar shear strength was τu = 38.7 MPa. For MWK–N–C/SiC pins, the double-shear strength was τu = 76.5 MPa, 99.7 MPa, and 79.6 MPa for test types I, II, and III, respectively. Compared with MWK–C/SiC pins, the double-shear strength of MWK–N–C/SiC pins all decreased, i.e., 26.7%, 50.8%, and 8% for test types I, II, and III, respectively. The MWK–N–C/SiC composite and pins possessed high interlaminar shear strength and double-shear strength, due to the needled fiber in the thickness direction, low porosity (10–15%), and high composite density (2.0 g/cm3).

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.

Utilization of Empty Fruit Bunch Derived Vapor for Carbon Deposition within Iron Ores

Metallurgical coke is the main source of fuel and reducing agent for iron and steel industry. Empty fruit bunch (EFB) biomass which is abundantly available in Malaysia could be utilized as a source of energy as well as reducing agent in iron making process. This research presents carbon infiltration within low-grade iron ore via chemical vapor infiltration (CVI) method from EFB pyrolysis vapor. Low-grade iron ore was first heated to remove the combined water (CW) that consequently created pore network within the iron ore. These pores would act as sites for carbon infiltration in the iron ore. The EFB treatment on iron ore has been carried out at different temperatures and the effect of pyrolysis temperature on the carbon infiltration has been investigated. The Brunauer−Emmet−Teller (BET) and Barrett−Joyner−Halenda (BJH) methods have been performed to analyze pore surface and pore volumes of the iron ore. Pore surface and pore volume decreased as the temperature increased indicated that more carbon has been deposited. Using X-ray diffraction (XRD) analysis, it was shown that the low-grade iron ore has been transformed into iron (Fe). The infiltrated carbon from the EFB pyrolysis vapor in the pore surface iron ore is proven to be able to be utilized as source of energy and reducing agent to partially replace metallurgical coke in the blast furnace in order to reduce emission of harmful gas.

Morphologies evolution and mechanical behaviors of SiC nanowires reinforced C/(PyC-SiC) multilayered matrix composites

• The bionic (PyC-SiC) n multilayered structure was used to improve flexural properties. • The SiC nanowires formed in-situ on the surface of multilayered structure played an important role in micro-zone reinforcements. • The (PyC-SiC) n multilayered structure and SiC nanowires were prepared at the same time, and they could form a multiscale reinforcing system. • The flexural strengths and flexural modulus of modified composites were up to 62.36% and 102.20% respectively higher than C/C composites. SiC nanowires reinforced C/(PyC-SiC) n multilayered matrix composites (SM-CS for short) were prepared by combined with sol-gel and chemical vapor infiltration (CVI) method. Firstly, (PyC-SiOC) n multilayered structure was formed by cycles of impregnation and deposition. Then SiOC was transformed into SiC by heat-treatment, and (PyC-SiC) n multilayered structure would be obtained. At the same time, the PyC layer which was designed as the outmost layer could decrease gas supersaturation to form in-situ tubular SiC nanowires on the surface of multilayered structure. The results of three-point bending test showed that the maximum force of SM-CS composites was increased by the number of cycles of the preparation process, which were up to enhanced by 74.38% compared with C/C composite materials. The fracture surface showed that the improvement was due to the multiscale reinforcing system of (PyC-SiC) n multilayered structure and SiC nanowires. Multilayered structure can protect carbon fibers and release stress concentration by induction of cracks. And the mechanical interlocking effect of SiC nanowires could reinforce bonding force of the remaining matrix.

Fiber reinforced SiC ceramic helical spring for high elasticity and large deformation at high temperature

AbstractCeramic spring devices play a significant role in mechanical systems, developing advanced ceramic helical spring with combination of high toughness and good elasticity still remains challenging. Herein, C/SiC composite helical springs with good elastic response to temperatures were fabricated by chemical vapor infiltration method. The C/SiC springs with rectangular and circular coil structures show high densities of 2.04 ± 0.162 and 1.96 ± 0.132 g/cm3, respectively. In contrast, C/SiC spring with circular coil structure can achieve high toughness of 0.92 ± 0.004 N/mm and low energy loss of 9.13 × 10−3 J at room temperature, while also exhibit an ideal spring constant of 0.35 N/mm and low energy loss of 7.82 × 10−2 J at 1000°C, which are highly comparable with those reported traditional ceramic springs. Furthermore, through finite element simulations, the stress distribution shows that both springs generate residual stresses at different temperatures after several cycles. The more uniform stress distribution and small irreversible deformation can be responsible for the superior elasticity of C/SiC spring with circular coil structure. The proposed strategy holds promising potential for developing C/SiC composite helical spring for future elastic devices used in complex and extreme service environments.

Effect of CVI SiC content on ablation and mechanism of C/C-SiC-ZrC-Cu composites

C/C-SiC-ZrC-Cu composites were fabricated by chemical vapor infiltration, precursor infiltration-pyrolysis and vacuum-pressure infiltration methods. During Cu infiltration, the Cu6·69Si and Cu3Si new phases are generated through reaction between SiC and molten Cu. The formed Cu6·69Si, Cu3Si, ZrC and SiC phases can improve the wettability and interface combination between Cu and the doped carbon matrix. The ablation tests demonstrate that the CVI SiC content significantly affects the structure of protective oxide layer, and induces inverse effects in ablation center at 2500 °C and 3000 °C. The relatively high CVI SiC content enhances the ablation resistance of composites at 2500 °C, but increases the linear ablation rate at 3000 °C due to the excessive evaporation and mechanical denudation. During ablation, the formed Si-Zr-C-O layer underneath ablation center and the Si-Cu-C-O layer on transition or marginal areas can prevent carbon matrix from serious oxidation. After ablation for 20 s, the C/C-SiC-ZrC-Cu composites with high CVI SiC content display the best anti-ablation property at 2500 °C, and the ablation rates are 3.5 ± 0.1 μm/s and 3.4 ± 0.1 mg/s.

Effect of pyrocarbon interphase texture and thickness on tensile damage and fracture in T‐700™ carbon fiber–reinforced silicon carbide minicomposites

AbstractIn this paper, T‐700™ carbon fiber–reinforced silicon carbide (C/SiC) minicomposites with pyrocarbon (PyC) interphase with different textural microstructure and thickness were fabricated using the chemical vapor infiltration method. The interface properties (i.e., textural microstructure, thickness, hardness, and modulus) were obtained through multiple testing methods (i.e., Raman spectroscopy, X‐ray diffraction, scanning electron microscopy, and nanoindentation tests). Relationships between the deposition temperature and residence time with the texture type (i.e., low, medium, and high texture) were established. Uniaxial tensile experiments were conducted for C/SiC minicomposites with different PyC interphases to characterize the composite's internal damage evolution and fracture. Relationships between the composite's tensile nonlinear damage evolution, fracture strength and strain, PyC interphase texture, and thickness were established. The composite's tensile strength and fracture strain were the highest for the C/SiC minicomposite with medium‐high texture PyC interphase. For the C/SiC minicomposite with the same texture interphase, the composite's tensile strength and fracture strain were affected by the coating thickness. The higher the thickness of the coating, the lower the composite's tensile strength and fracture strain.