SiC Deposition Research Articles

Three-point bending damage detection of SiC coated C/C composites based on acoustic emission

In this study, the three-point bending process of needled C/C composites, pack cementation SiC coated-C/C composites (PC-SiC-C/C) and chemical vapor deposition SiC coated-C/C composites (CVD-SiC-C/C) were monitored by the acoustic emission (AE) technology. To study the bending damage evolution process of three kinds of composite materials, the K-means algorithm was used to analyze the AE characteristic parameters. The damage type was analyzed by combining the electron microscope image of the sample fracture. The findings revealed that C/C composites and CVD-SiC-C/C composites contain three distinct types of damage: matrix cracking, carbon fiber-pyrolytic carbon interface debonding, and fiber fracture under three-point bending loading. PC-SiC-C/C composites has two additional damage: coating cracking and pyrolytic carbon-SiC interface debonding. The various damages could be identified by different AE signals: matrix cracking (175.781–421.875 KHz), carbon fiber-pyrolytic carbon interface debonding (70.312–164.062 KHz), fiber fracture (2.929–46.875 KHz), coating cracking (375–585.937 KHz), pyrolytic carbon-SiC interface debonding (169.921–257.812 KHz). The cumulative AE energy shows that the order of damage types of the three composites during the three-point bending loading is different.

Boosting computational thermodynamic analysis of the CVD of SiC coating via machine learning

Although thermodynamic analysis provides the possibility to perform a full-range study on the chemical vapor deposition (CVD) of SiC, billions of calculations are required to achieve a high-resolution study for such a high-dimensional space. Similar issues are also encountered for other materials modeling and simulation techniques. Therefore, using the database from the thermodynamic analysis of CVD of SiC as an example, we demonstrate a machine learning framework to accelerate physical-based materials modeling and simulations. Using only 6 % of randomly selected data generated in the thermodynamic analysis of CVD of SiC, a high-fidelity random forest (RF) with an accuracy (R2) of close to 1 was obtained. The derived key CVD metrics, i.e., deposit purity, deposition efficiency of SiC, and precursor utilization efficiency by the RF model are in excellent agreement with those determined by thermodynamic analysis.

Effects of deposition temperature on microstructures and ablative properties of SiC coatings prepared by CVD from methylsilane

Using the methylsilane (MS) as a gas precursor, SiC coatings were prepared on the surface of graphite by the chemical vapor deposition (CVD) method at different deposition temperatures. The effects of temperature on the deposition rate, microstructures and ablative properties of SiC coatings were investigated systematically. The results showed that the SiC deposition rate of SiC coating using MS at 1000 °C was 50–120 μm/h, which was much higher than that using methyltrichlorosilane (5–10 μm/h). The SiC coatings deposited at lower temperatures (900–1000 °C) exhibited smooth and spherical compact packing morphology, while the SiC coatings deposited at higher temperatures (1100–1200 °C) appeared to possess an irregular cauliflower morphology with an significantly increased size of SiC particles. Therefore, the SiC coating prepared at deposition temperature of 1000 °C had suitable density, roughness, and uniform size of coating microstructure. Meanwhile, the mass ablation rate and linear ablation rate of the obtained SiC coating were respectively 0.0096 mg/s and 0.3750 μm/s after plasma ablation at 2300 °C for 80 s, exhibiting excellent ablative resistance. This study provided a theoretical and technical foundation for the preparation of SiC coating using the MS as the gas precursor by the CVD method.

Erosion and deposition regulate soil carbon by mediating Fe-Carbon fixation mode in a typical catchment in the black soil region of Northeastern China

Soil carbon is critical to soil quality and the global carbon cycle, while Fe is highly sensitive to redox processes and can affect soil carbon stocks by sequestrating and releasing carbon. Soil erosion and deposition can cause the spatial heterogeneity of soil properties along landscapes and alter the redox environment, thus further influence carbon fixation by Fe in situ. Carbon, especially Fe-oxide-bound carbon (OC-Fe) were poorly studied in different erosion intensities. Here, we investigated OC-Fe, soil organic carbon (SOC), and inorganic carbon (SIC) contents at erosion and deposition sites in a typical catchment of Northeast China, and evaluated the responses of oxygen diffusion state (DCo), Fe oxides (Fep, Fed) and valence state of Fe (Fe(II), Fe(III)) to erosion and deposition. We have also quantified factors affecting Fe and carbon to elucidate the drivers of Fe-mediated carbon stock variations induced by erosion. Results showed that with a higher erosion intensity, a greater redistribution was emerged on OC-Fe and SIC in the 0–10 cm soil layer of study catchment. Compared to deposition sites, OC-Fe and SIC increase by 63.32 % and 11.41 times at erosion sites, respectively. However, SOC increased 18.56 % at deposition sites. In the 10–20 cm soil layer, where erosion forces were more pronounced, the binding mode of Fe oxides to carbon changed from co-precipitation to adsorption. The presence of Fe(II) promoted OC-Fe formation. Structural equation modelling（SEM）constructed by the varied particle composition with erosion and deposition explained 79 % of the variation in carbon stock in 0–20 cm soil layer. This study concluded that subsoil carbon stocks (>10 cm) are mainly affected by the application rate of exogenous carbon and variations of its mineral content. Erosion-induced variations of carbon sequestration patterns have continuous effects on farmland carbon turnover capacity.

High-throughput thermodynamic study of SiC high-temperature chemical vapor deposition from TMS-H2

A systematic study on the tetramethylsilane-hydorgen (TMS-H2) system by high-throughput thermodynamic method is conducted with a large experimental condition range (500 ∼ 2700 K, 0 ∼ 75 kPa, and H2:TMS ratio of 0.1 to 10000) towards the deposition of pure single-crystal SiC by high-temperature chemical vapor deposition (HTCVD) method. The temperature, pressure and H2:TMS ratio dependence phase diagrams are calculated to describe the deposition condition of single-phase “gas + SiC” region. Due to the etching effect of hydrogen on graphite, the increasing temperature and pressure could suppress the formation of graphite and favor the growth of SiC in the H2:TMS ratio above 1000, however, excessive H2:TMS ratio could reduce the TMS consumption efficiency. TMS consumption efficiency maps focusing on the gas + SiC region based on the phase diagrams have been carried out to balance the deposition parameters, SiC mole fraction and TMS consumption efficiency. When H2:TMS ratio > 1000, an accepted window for preparing single-phase SiC with a high TMS consumption efficiency (>90%) is provided, and this window could expand furtherly with increasing the ratio. TMS consumption efficiency maps offer the theoretic basis and guidance for improving the quality and cost of industrial production of single-crystal SiC by HTCVD method.

Effects of thermal annealing on thermal conductivity of LPCVD silicon carbide thin films

The thermal conductivity (k) of polycrystalline SiC thin films is relevant for thermal management in emerging SiC applications like microelectromechanical and optoelectronic devices. In such films, k can be substantially reduced by microstructure features including grain boundaries, thin film surfaces, and porosity, although these microstructural effects can also be manipulated through thermal annealing. Here, we investigate these effects by using microfabricated suspended devices to measure the thermal conductivities of nine low-pressure chemical vapor deposition SiC films of varying thicknesses (from 120 to 300 nm) and annealing conditions (as-grown and annealed at 950 and 1100 °C for 2 h, and in one case 17 h). Fourier-transform infrared spectroscopy, x-ray diffraction spectra, and density measurements are also used to characterize the effects of annealing on the microstructure of selected samples. Compared to as-deposited films, annealing at 1100 °C typically increases the estimated grain size from 5.5 to 6.6 nm while decreasing the porosity from around 6.5% to practically fully dense. This corresponds to a 34% increase in the measured thin film thermal conductivity near room temperature from 5.8 to 7.8 W/m K. These thermal conductivity measurements show good agreement of better than 3% with fits using a simple theoretical model based on the kinetic theory combined with a Maxwell–Garnett porosity correction. Grain boundary scattering plays the dominant role in reducing the thermal conductivity of these films compared to bulk single-crystal values, while both grain size increase and porosity decrease play important roles in the partial k recovery of the films upon annealing. This work demonstrates the effects of modifying the microstructure and, thus, the thermal conductivity of SiC thin films by thermal annealing.

Interfacial modification and oxidation resistance behavior of a CVD-SiC coating for C/SiC composites

The root structure was introduced to mainly improve the oxidation resistance and bonding strength of chemical vapor deposition (CVD) SiC coating on C/SiC composites. The microstructure, phase composition, bonding strength, and thermal cycling performance of SiC coatings with root structure were investigated. The results indicated that the designed and prepared root structure, consisting of pores and SiC nanowires, improved the bonding strength between the matrix and SiC coating. The tensile strength of the coating increased to over 4.67 MPa. The root structure reduced coating cracking or spalling by relieving thermal stress, inhibiting the propagation of cracks, and improving bonding strength. The oxidation resistance of coating could be effectively increased. After 9 thermal cycles between 1873 K and room temperature, the weight loss was only 0.48 wt%.

High-throughput thermodynamic analysis of the CVD of SiC from the SiCl4-CH4-H2 system

A high-throughput thermodynamic analysis based on the CALPHAD approach is employed in this study to gain insights into the chemical vapor deposition (CVD) of SiC from the SiCl4-CH4-H2 system using up-to-date thermodynamic databases. The explored deposition conditions, i.e., temperature, pressure, C/Si ratios and H2/SiCl4 ratios, ranges from 800 to 1800 °C, 400 to 40,000 Pa, 0.1 to 10 and 0.1 to 200, respectively. In addition to the metrics of deposit purity and deposition efficiency of SiC, a new metric, i.e., the utilization efficiency of precursors, is proposed in this work to facilitate the identification of the optimal deposition conditions. The influence of deposition parameters and precursor compositions on the compositions and phase stabilities of the condensed and gas phases pertinent to vapor processing are elucidated. The results show that the deposit purity is more sensitive to temperature than pressure. The optimal conditions to achieve high deposit purity (100 %), deposition efficiency (99.74 %) and the utilization efficiency of precursors (99.74 %) locate on the C/Si ratios between ~0.8 and ~ 1, H2/SiCl4 ratios above 8, low pressure (below 10 kPa) and medium temperatures (~ 1000 to ~1400 °C). Furthermore, low C/Si ratios (< 0.5) and high C/Si ratios (> 1) lead to the formation of free Si and graphite, respectively.

Adsorption on 3C-SiC surfaces in chemical vapor deposition process of CH3SiCl3–H2 system: a first-principles study

SiC has become increasingly important in high-energy semiconductor device materials and structural composite materials in recent years. Many systematic experimental studies have been conducted on the preparation of cubic silicon carbide (3C-SiC) by the chemical vapor deposition (CVD) process. Despite this, the microscopic mechanism of the SiC deposition process has not been fully elucidated due to the limitations of the experimental methods. Based on these problems, the structural parameters, adsorption energies, charge populations, transition states, and electronic densities of states of Si-Cl-C-H at different sites were simulated by a first-principles method, and the micro-mechanism of the surface deposition reaction was analyzed. The calculated results provide a theoretical and experimental basis for the study of 3C-SiC preparation by CVD.

Effect of temperature on the interaction between CVD SiC ceramic and nickel-based alloy in molten LiF-NaF-KF salt

The effect of temperature on the interaction between chemical vapor deposition SiC and GH3535 alloy in molten LiF-NaF-KF salt was investigated. Results indicate that temperature is critical to the interaction. At 500 and 600 °C, SiC and alloy did not interact with each other. The interaction happened at 650 °C and higher temperature by reactions among SiC, alloy, and their corrosion products. The corrosion products of alloy reacted with SiC to form Cr3C2, and the corrosion products of SiC reacted with Ni to form Ni31Si12 and Ni2Si on the surface of alloy. Depths of corrosion and deposition increased with temperature.

Fabrication of Aluminum 5083/SiC Surface Composite on Tungsten Inert Gas Weld Joint by Novel Direct Friction Stir Processing Technique

For the creation of surface reinforcement particles in the metal matrix, friction stir processing is frequently utilized. Formation of aluminum/SiC surface composite on Tungsten Inert Gas (TIG) butt weld of Al5083 by a novel technique of direct friction stir processing (DFSP) using a hollow tool is successfully demonstrated in this present work. Deposition of SiC in the stir zone of DFSP was confirmed by X-Ray diffraction (XRD) method. Micro analysis of weld joint was achieved using metallographic microscope and scanning electron microscope (SEM). Microstructure of stir zone of DFSP shows finely distributed SiC reinforcement particles in aluminum matrix. Absence of detrimental intermetallics was confirmed by energy dispersive spectroscopy (EDS) analysis. Tensile strength of DFSPed specimen was found to be 227.3 MPa which is 19.5% lower than UTS of autogenous TIG weld specimen. Microhardness of SZ of DFSP was found to be increased from TIG weld microhardness of 86 Hv to 107 Hv due to presence of SiC particles.

A New Two-Step Method for Laser Cladding of Silicon Carbide in Wc-Co Substrates

WC-Co cutting tools are widely used by the metalworking industry. In order to improve the properties of these tools, research on the application of wear-resistant coatings, such as polycrystalline diamond, are of great importance to several applications. It is known that the occurrence of high-stress levels between the coating and the substrate can lead to adhesion failures. One strategy to minimize these failures is applying an intermediate layer of SiC. In this work, the deposition of a SiC layer was carried out by a novel two-step laser cladding approach. Instead of cladding directly the pre-synthesized SiC on the substrates, a 200 µm silicon powder layer was pre-deposited on the WC-Co substrates and then irradiated with a 30 W CO2 laser. To improve metallurgical bonding between the tungsten and the Si layer, all substrates were chemically attacked. This attack allows cobalt removal from the surface and increases surface roughness, improving the laser cladding process. After the SiC laser cladding, samples were coated with a 200 µm graphite powder layer and irradiated again by a CO2 laser. The samples were characterized by SEM, EDS, and XRD analysis. The results showed that in the first step, an irradiation energy of about 0.27 J was enough to fuse the silicon powder to the substrate and in the second step, 0.13 J was enough to promote the reaction between silicon, carbon and the WC substrate, resulting in the in-situ synthesis of SiC. Finally, a new method was proposed for the deposition of SiC on WC-Co based substrates and the observed results allowed the proposal of an empirical equation to describe the chemical reactions of the process.

The Effect of Silicon-Containing Minerals on Coal Evolution at High-Temperature Pre-Graphitization Stage

Coal is a carrier of carbon enrichment, so it has the potential for the preparation of coal-based carbon materials. In this paper, LT anthracite and TSG bituminous coal were selected, and the corresponding graphitized samples were prepared from high-temperature treatment. The effects of silicon-containing minerals on coal evolution during the high-temperature pre-graphitization stage were investigated by XRD, Raman spectroscopy, and SEM. The results showed that with increasing temperature, the silicon-containing samples showed smaller d002 and ID1/IG, and higher Lc, while La presented a slight increase. It was found by SEM that the micromorphology of all samples was mainly massive structures. Meanwhile, irregular polyhedral structures also were observed in silicon-containing samples at 1300 °C, which were related to the formation and deposition of SiC. The carbothermal reactions of silicon-containing minerals continued to generate SiC and precipitate with increasing temperature, resulting in the gradual transformation of the needle-like structures into polyhedral structures. However, SiC was completely decomposed at 2800 °C. These changes indicated that during the pre-graphitization stage, silicon-containing minerals form SiC to advance the reduction of the interlayer spacing and the increase of longitudinal layer stacking height, thereby enhancing structural ordering and graphitization degree, while it had less effect on the lateral size. This will help to further understand the role of silicon-containing minerals in the coal pre-graphitization stage and also provide useful information about synthetic coal-based graphite.

Residual Stress Simulation of Heterogeneous Cladding Layer Between SiC/Ti6Al4V

SiC cladding on the alloy surface can significantly improve the high temperature resistance and oxidation resistance of the material. However, heterogeneous cladding usually produces large residual stress and affects the service life of the material. In the process of laser cladding simulated by finite element method, the mechanism of residual stress during SiC deposition on alloy surface is studied by using moving double ellipsoid heat source model. The simulation results show that the residual stress is unevenly distributed near the cladding layer, and the residual stress presents a compression-tension-compression distribution in the thickness direction due to the mixing law of material properties, which provides a reliable numerical prediction method for the residual stress of SiC cladding layer cladding on the alloy base.

Direct energy deposition of SiC reinforced Ti–6Al–4V metal matrix composites: Structure and mechanical properties

The creation of metal matrix composites (MMCs) is an important strategy for obtaining heat-resistant products. Metal matrix composites provide superior characteristics of improved mechanical, high-temperature and tribological properties. Manufacturing of MMCs by the methods of additive technologies contributes to the development of technical industries. In this paper, the formation of the structure, phase composition and mechanical properties of Ti–6Al–4V/SiC MMCs got by direct energy deposition were investigated. The compositions with 1 vol%, 3 vol%, 5 vol%, 7 vol% SiC are considered. The structure consists of SiC particles surrounded by a matrix of titanium martensite. However, during deposition, the matrix interacts with SiC particles to form TiC and Ti5Si3. Increasing the amount of ceramic content leads to a reduction of grains, which is associated with the formation of TiC at the grain boundaries. As the SiC content increases, the hardness increases because of an increase in the solid phases TiC and Ti5Si3, but these phases weaken the DED samples. The addition of 1 vol% SiC significantly increases the strength of the titanium alloy up to 1300 MPa with a relative elongation of 2.1%.

Models for Impurity Incorporation during Vapor-Phase Epitaxy

Impurity incorporation during vapor-phase epitaxy on stepped surfaces was modeled by classifying rate-limiting processes into i) surface diffusion, ii) step kinetics, and iii) segregation. Examples were shown for i) desorption-limited Al incorporation during chemical vapor deposition (CVD) of (0001) SiC, ii) preferential desorption of C atoms from kinks during CVD of Al-doped (000-1) SiC, and iii) segregation-limited C incorporation during metalorganic vapor-phase epitaxy of (0001), (000-1), and (10-10) GaN.

Investigating the Use of C/SiC Ceramic Composites in an Innovative Light-Water Reactor Core Grouping Catcher

China Nuclear Power Engineering, Northwestern Polytechnical University, and Beijing Institute of Technology have undertaken a joint research work with the goal of developing corium retention containers for use in an innovative light-water reactor core grouping catcher (CGC). In Serious Accidents (SAs), the corium will be retained in the C/SiC ceramic composite spherical shell container and thrown into the pool for passive cooling. In order to investigate the capability of the C/SiC ceramic composites to withstand the high temperature of 1800°C and the huge thermal shock at the initial stage of cooling, in this work, the high-temperature performance of these composites is studied. Furthermore, the compatibility of these composites with corium is investigated, and a retention container design prototype is proposed. The thermal conductivity, thermal expansion coefficient, high-temperature tensile strength, and thermal shock resistance of the candidate C/SiC specimens to be used in the manufacturing of the detention container are measured. The FactSage software package is used for the chemical compatibility study and product composition analysis of the composite SiC deposition layer and corium. The corrosion process of the SiC deposition layer of the composite material caused by corium is investigated through high-temperature corrosion tests and the electron microscopy analysis of the SiC specimen with the incorporation of CeO2. The results show that the C/SiC ceramic composite can meet the design criteria of the CGC corium retention container, and it is impossible to cause a carbon reaction disaster through the failure of the composite SiC deposition layer.

Microstructure and Thermal Property of Inert Plasma-Sprayed Tungsten Coating on SiC-Coated Carbon/Carbon Composites

The coating technology of tungsten on carbon/carbon (C/C) composite is an important issue for fusion experimental device components. In this study, an interlayer of chemical vapor deposition SiC between tungsten coating and C/C substrate was used. A tungsten coating 320 μm thick was successfully deposited on SiC-coated C/C substrate by inert plasma spray. The microstructure, roughness, and constituents of W-SiC-C/C composite materials were investigated using a scanning electron microscope, energy dispersive X-ray spectroscope, X-ray diffractometer, and atomic force microscope. The tungsten coating structure that may prevent crack propagation essentially consisted of a stacked lamellar columnar microstructure and particle cluster microstructures. The interfaces between the tungsten and SiC coating and between the SiC coating and the C/C were clear. The SiC interlayer acts as a barrier for carbon and tungsten diffusion. The thermal conductivity of the system was calculated by the mixture rule, which was 47.33 to 82.35 W/(m·K). The thermal expansion coefficient of W-SiC-C/C was negative at room temperature and up to 1.5 × 10−6/K for elevated temperature.

Fabrication and characterization of SiC sandwich material for Flow Channel Inserts in HT-DCLL blanket by gel casting

Flow Channel Inserts (FCIs) are key elements in the high temperature DCLL blanket concept since they provide the required thermal insulation between the He-cooled structural steel and the hot PbLi flowing at a maximum temperature of 700 °C, and the necessary electrical insulation to minimize magnetohydrodynamic (MHD) effects. In this paper, the use of SiC-sandwich material for FCIs consisting of a porous SiC core (thermal and electrical insulator) covered by a dense Chemical Vapor Deposition (CVD) SiC layer (protection against PbLi infiltration) has been studied. Lab-scale FCI prototypes were produced by the gel casting method and characterized in terms of thermal and electrical conductivities (the latter before and after exposure to ionizing radiation) and flexural strength. Corrosion tests under flowing PbLi at 500–700 °C in presence of a magnetic field up to 5 T were performed obtaining promising results regarding the reduction of MHD pressure drop and the compatibility of SiC and PbLi under dynamic conditions. Additionally, thermomechanical finite elements simulations were performed in a 3D channel geometry to identify black spots regarding thermal stresses.

Swirl cast with wire cut electric discharge machining for investigational purposes on Al-7075/Al2O3&SiC

The real applications of aluminium metal matrix composites encompass aerospace, armed services, automotive, aerobics instruction equipment, and electronics, and many are esteemed for innovative complementary properties such as illumination mass, enhanced effectiveness, and coefficient of thermal extension. The feasible Al 7075 alloy is widely used in aerospace manufacturing constituents in terms of structural mechanism incremental improvement. Throughout this preliminary investigation, Al-7075 was toughened amid rising 2, 4, 6, and 8 influence support in expressions of entitlement to Al203 and 3 influence support in expressions of proportionality of SiC, being genuine and genuine man-made, and utilizing the swirl transmission method. Stiffness, elongation, impact, and wear test specimens are positioned in accordance with international standards. The casting process is finished, and up to 8% silicon carbide and aluminium oxide residue will be effectively added to aluminium by using a swirl transmission technique to produce Al-HMC. By enabling the absorption of Al203 and SiC residues, this AL-HMC improved stiffness and tensile strength. When the concentration of Al203 and SiC deposits within the AMC increases, wear and frictional strength decrease. When the percentage of Al203 and SiC in the MMC is significantly increased, the variation in collision intensity becomes minor. The L9 Array in Combination with DOE Techniques this investigation to establish various WEDM process parameters is also enforced into demographic groups with the purpose of improving minimal surface roughness along with MRR for Al7075, Al203, and SiC. It must have been discovered that enhancing the weight percent of Al203 and SiC pilot in addition to increasing surface roughness also reduced MRR. The findings of the study were used to select the fastest and most accurate WEDM Process parameters for attempting to make precision engineering components of HMMC of Al 7075 with Al203 and SiC at various weight percents.