SiC Deposition Research Articles

Morphological study of SiC coating developed on 2D carbon composites using MTS precursor in a hot-wall vertical reactor

AbstractSilicon carbide coating was developed using chemical vapor deposition on carbon substrate as a protective coating. The present studies were carried out with methyl trichlorosilane as the SiC precursor, at 1673 K along with hydrogen and argon as carrier gas using a high-temperature vertical graphite reactor. The SiC coatings were characterized by means of X-ray diffraction for phase identification. Scanning electron microscopy analysis with energy dispersive X-ray spectrometer was also carried out for microstructure and elemental analysis. From the morphological study of different SiC deposits obtained at varying operating parameters it was observed that methyl trichlorosilane feed rate and hydrogen flow rate play a major role in deciding the nature of deposits and the argon percentage in the mixed gas also plays a vital role.

Microstructure of TRISO coated particles from the AGR-1 experiment: SiC grain size and grain boundary character

Pre-irradiation SiC microstructures in tristructural-isotropic (TRISO) coated fuel particles from the Advanced Gas Reactor Fuel Development and Qualification program’s first irradiation experiment (AGR-1) were quantitatively characterized using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). From EBSD, it was determined that only the cubic polymorph of as-deposited SiC was present and the SiC had a high fraction of coincident site lattice (CSL) Σ3 grain boundaries. Additionally, the local area misorientation (LAM), which is a qualitative measurement of strain in the SiC lattice, was mapped for each sample fuel variant. The morphology of the SiC/IPyC interfaces were characterized by TEM following site-specific focused ion beam (FIB) specimen preparation. It was determined that the SiC layer had a heavily faulted microstructure typical of chemical vapor deposition (CVD) SiC and that the average grain diameter increased radially from the SiC/IPyC interface for the samples manufactured with similar CVD conditions, while the last sample showed a nearly constant grain size across the layer.

ZrB2/SiC as a protective coating for C/SiC composites: Effect of high temperature oxidation on mechanical properties and anti-ablation property

C/SiC composites are raising great interest as a thermal shielding for aerospace applications, provided that they are protected from oxidation by suitable coatings. Conversely, ultra high temperature ceramics, and in particular ZrB2, is among the best oxidation resistant materials as known. A new type of oxidation protective coating (ZrB2/SiC coating) was produced on C/SiC composites. The composites were produced by precursor infiltration and pyrolysis (PIP), which is a simple and low cost method; the coating was ZrB2 mixed with SiC, which was fabricated by painting slurry on the surface of the composite followed by chemical vapor deposition (CVD) SiC on the top. Mechanical tests were conducted before and after oxidation test. Anti-ablation property was tested under oxy-acetylene torch. Oxidation test shows that the uncoated samples are oxidized quickly and the weight loss reaches 29.2% and the reservation of original flexural strength is only 6.74%, while the weight loss of ZrB2/SiC coated samples is only 5.19%, and the reservation of original flexural strength is 37.4%. ZrB2/SiC coating can provide longtime protection for C/SiC composites at 1973K. Compared with the uncoated composites, the linear and mass ablation rates of the coated composites decreased by 62.1% and 46.1%, respectively, after ablation for 30s. The formation of zirconia and silicon dioxide from the oxidation of ZrB2/SiC improved the ablation resistance of the composites, because of the evaporation at elevated temperature, which absorbed heat from the flame and reduced the erosive attack to carbon fibers and SiC matrix.

Effects of Residence Time and Reaction Conditions on the Deposition of SiC from Methyltrichlorosilane and Hydrogen

The overall growth kinetics of silicon carbide films deposited from the mixture of methyltrichlorosilane (MTS) and hydrogen were determined by a magnetic suspension microbalance. The results show that three regions are distinguishable in the studied temperature range. In low temperatures (<1000°C), the deposition process is controlled by surface chemical reaction mechanism. The deposition rate has a weak dependence on temperature, and the activation energy is 188 kJ/mol. In mediate temperatures (1100°–1300°C), the deposition rate rapidly increases with increasing temperature, and the activation energy is 100 kJ/mol. The transition temperature of the above two deposition mechanisms lies in 1000°–1100°C. The complex relation between the deposition rate and total pressure can be explained by these two reaction mechanisms, depending on the competition between the residence time and concentrations of precursors. Both the flow rate and the distance into the chemical vapor deposition reactor strongly influence the reactivity. Longer residence time and larger distance of the substrate in reactor lead to decreasing deposition rate, mainly due to the reactant depletion on the wall, decomposition of MTS as well as the concentration of HCl.

Effect of particle concentration on the structure and tribological properties of submicron particle SiC reinforced Ni metal matrix composite (MMC) coatings produced by electrodeposition

In the present work, a nickel sulfate bath containing SiC submicron particles between 100 and 1000nm was used as the plating electrolyte. The aim of this work is to obtain Ni–SiC metal matrix composites (MMCs) reinforced with submicron particles on steel surfaces with high hardness and wear resistance for using in anti-wear applications such as dies, tools and working parts for automobiles and vehicles. The influence of the SiC content in the electrolyte on particle distribution, microhardness and wear resistance of nano-composite coatings was studied. During the electroplating process, the proper stirring speed was also determined for sub-micron SiC deposition with Ni matrix. The Ni films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The depositions were controlled to obtain a specific thickness (between 50 and 200μm) and volume fraction of the particles in the matrix (between 0.02 and 0.10). The hardness of the coatings was measured to be 280–571HV depending on the particle volume in the Ni matrix. The tribological behaviors of the electrodeposited SiC nanocomposite coatings sliding against an M50 steel ball (Ø 10mm) were examined on a tribometer. All the friction and wear tests were performed without lubrication at room temperature and in the ambient air (with a relative humidity of 55–65%). The results showed that the wear resistance of the nanocomposites was approximately 2–2.2 times more than those of unreinforced Ni.

Raman analysis of epitaxial graphene grown on 4H—SiC (0001) substrate under low pressure condition

In this paper, we report a feasible route of growing epitaxial graphene on 4H—SiC (0001) substrate in a low pressure of 4 mbar (1 bar=105 Pa) with an argon flux of 2 standard liters per minute at 1200, 1300, 1400, and 1500 °C in a commercial chemical vapour deposition SiC reactor. Using Raman spectroscopy and scanning electron microscopy, we confirm that epitaxial graphene evidently forms on SiC surface above 1300 °C with a size of several microns. By fitting the 2D band of Raman data with two-Lorentzian function, and comparing with the published reports, we conclude that epitaxial graphene grown at 1300 °C is four-layer graphene.

Fabrication of SiC–SiC composites for fuel cladding in advanced reactor designs

Both advanced fission reactor concepts and fusion energy systems demand materials that can survive extremely harsh operating environments having persistent high temperature and high neutron flux conditions. Silicon carbide fiber/silicon carbide matrix (SiC–SiC) composites have shown promise for these applications, which include fuel cladding and reactor structural components. However, the composite fabrication process is time consuming and the fabrication of complicated geometries can be difficult.In this work, SiC–SiC and carbon fiber–SiC composite samples were fabricated using chemical vapor infiltration (CVI), and the mechanical and thermal properties of samples with a range of densities and total infiltration times were characterized and compared. Both sample density and the reinforcing fiber material were found to have a very significant influence on the composite mechanical and thermal material properties. In particular, internal porosity is found to have a significant effect on the mechanical response, as can be observed in the crack propagation in low density samples. In order to better understand the densification of the composites, a computer model is being developed to simulate the diffusion of reactants through the fiber preform, and SiC deposition on the fiber surfaces. Preliminary modeling has been correlated with experimental results and shows promising results.

STRUCTURE AND PHOTOLUMINESCENT PROPERTIES OF SiCO THIN-FILMS DOPED WITH Al PREPARED BY DUAL MAGNETRON SPUTTERING

SiCO thin-films doped with aluminum (Al) prepared by alternate deposition of SiC and Al thin layers using Ar and O 2 as sputtering gas were deposited on n- Si substrates. The as-deposited thin-films were annealed under 600°C in nitrogen ambient. The thin-films have been characterized by atomic force microscopy, energy dispersive spectrometer, X-ray diffraction, fourier transform infrared spectroscopy, and photoluminescence spectra. The results showed that the introduction of Al promotes the formation of Si — C bonds, but hinders amorphous SiC to further transform to crystalline SiC . The doped Al would react with SiO x in the thin-films to form more Si particles which strongly affect the optical properties. After Al doped, there presented a seven times of enhancement emission band centered around 412 nm, which is ascribed to nanostructure Si -related defect centers embedded in the SiCO thin-films. The obtained results are expected to have important applications in modern optoelectronic devices.

A carbon nanotube–enhanced SiC coating for the oxidation protection of C/C composite materials

A carbon nanotube–enhanced SiC (CNT–SiC) coating was deposited on C/C composites to improve the oxidation resistance of C/C. The CNT–SiC coating was prepared by direct growth of CNTs on C/C surface at 700 °C followed by deposition of SiC using chemical vapor deposition at 1150 °C for 1 h. SiC was deposited on the CNTs as well as the interface between CNTs and C/C, making CNTs strongly rooted on C/C surface. The final CNT–SiC coating consisted of two layers: the CNT–SiC layer and SiC layer. In comparison to the SiC coating, the CNT–SiC coating showed fewer cracks and a better oxidation resistance because the CNTs reduce the stress in the coating caused by the mismatch of the coefficient of thermal expansion between C/C and SiC.

Wear resistance enhancement of the titanium alloy Ti–6Al–4V via a novel co-incident microblasting process

In this study a room temperature coating deposition technology was investigated as a means of enhancing wear resistance of the titanium alloy Ti–6Al–4V. This process, termed CoBlast™, consists of co-incident particle streams of abrasive and coating materials which impact a substrate to create a modified surface. Al 2O 3 powder was chosen as the abrasive, while Teflon, SiC and B 4C powders were investigated as coating precursors. Ti–6Al–4V surfaces modified via CoBlast using either Al 2O 3–SiC or Al 2O 3–B 4C powder mixtures both demonstrated increased hardness compared with the unmodified alloy, however, wear testing performed using a pin-on-disc tribometer revealed that this did not translate to an appreciable improvement in wear resistance performance. In contrast, under the same wear test conditions, Al 2O 3–Teflon CoBlast modified Ti–6Al–4V demonstrated a significantly reduced friction coefficient and average pin-on-disc wear track widths and depths of 68 and 90% less than those which formed on the unmodified alloy. Through the deposition of either SiC or B 4C coatings in combination with a Teflon top layer a further improvement in wear resistance was confirmed by a 81/97% reduction in wear track width/depth. In conclusion, the deposition of Teflon coatings onto unmodified, SiC modified or B 4C modified Ti–6Al–4V using the CoBlast process yielded surfaces with significantly enhanced wear performance.

Investigation of the Growth of 3C-SiC on Si by Vapor-Liquid-Solid ( VLS ) Transport

In this work, the growth by Vapour-Liquid-Solid (VLS) mechanism of 3C-SiC on silicon substrate is reported. Firstly, a germanium layer is deposited on the substrate. Then the temperature of the sample is increased above Ge melting point in order to form a SiGe liquid phase by reaction with the substrate. Upon reaching the target temperature (1100-1300°C) the VLS growth starts with the injection of propane in the reactor. Both Raman spectrometry and X-Ray diffraction analyses evidenced the formation of 3C-SiC on every sample. However, this SiC deposit, a few micrometers thick, is always found to be polycrystalline though textured. In parallel, the presence of an epitaxial Si-Ge alloy, whose composition depends on the growth temperature, was systematically detected between Si and SiC.

Chlorinated precursor study in low temperature chemical vapor deposition of 4H-SiC

Low temperature (1300 °C) chemical vapor deposition (CVD) of SiC has gained interest in the last years for being less demanding in terms of reaction chamber lifetime, but also for allowing higher p-type dopant incorporation. Chloride-based CVD at low temperatures has been studied using chloromethane with tetrachlorosilane or silane, respectively and with or without controlled HCl addition. In this study we explore the use of methyltrichlorosilane (MTS) at growth temperatures (1300 °C) significantly lower than what is commonly used for homoepitaxial growth of SiC (1600 °C). MTS is a molecule containing all the needed precursor atoms; its effects are compared to the standard CVD chemistry, consisting of silane, ethylene, and HCl. Very different chemistries between the two precursor systems are proposed; in the case of MTS, C/Si ratios higher than 1 were required, however using the standard chemistry ratios lower than 1 were needed to obtain a defect-free epitaxial layer. We also demonstrate the need of using Cl/Si ratios as high as 15 to achieve a growth rate of 13 μm/h for 8° off-axis 4H-SiC epitaxial layers at 1300 °C. Limitations due to the low growth temperature are discussed in light of the experimental evidence on the growth mechanism as determined by the morphology degradation and the limited growth rate. Finally a comparison between the epilayers morphology obtained on 4H-SiC substrates with different off-cuts are presented, confirming the importance of lower C/Si ratios for 4° off-axis material and the inevitable growth of the cubic SiC polytype on on-axis substrates.

Microstructural and compositional characterisation of the pyrocarbon interlayer in SiC coated low density carbon/carbon composites

SiC coated carbon bonded carbon fibre (CBCF) composites, a special class of carbon/carbon composites for thermal insulation, were investigated. Successful deposition of SiC requires the CBCF material to be first given a pyrocarbon coating. SiC coating on pyrocarbon coated CBCF was assessed using several analytical techniques. X-ray diffraction identified the coating as β SiC. The fibre orientation in two perpendicular planes was determined using X-ray microtomography, and it was found to be random in one plane whereas there was a preferred orientation in the other plane. A comparison was made between the uncoated and pyrocarbon coated substrates in terms of surface roughness, purity and crystallinity, using white light interferometry, neutron activation analysis/secondary ion mass spectrometry and transmission electron microscopy, respectively. The higher roughness, greater purity and increased levels of crystallinity of pyrocarbon coated CBCF are considered to be responsible for the successful deposition of a SiC coating on this material.

Microstructure evolution of Ti–Si–C–Ag nanocomposite coatings deposited by DC magnetron sputtering

Nanocomposite coatings consisting of Ag and TiC x ( x < 1) crystallites in a matrix of amorphous SiC were deposited by high-rate magnetron sputtering from Ti–Si–C–Ag compound targets. Different target compositions were used to achieve coatings with a Si content of ∼13 at.%, while varying the C/Ti ratio and Ag content. Electron microscopy, helium ion microscopy, X-ray photoelectron spectroscopy and X-ray diffraction were employed to trace Ag segregation during deposition and possible decomposition of amorphous SiC. Eutectic interaction between Ag and Si is observed, and the Ag forms threading grains which coarsen with increased coating thickness. The coatings can be tailored for conductivity horizontally or vertically by controlling the shape and distribution of the Ag precipitates. Coatings were fabricated with hardness in the range 10–18 GPa and resistivity in the range 77–142 μΩ cm.

Chloride-Based SiC Epitaxial Growth toward Low Temperature Bulk Growth

In this study, chloride-based chemical vapor deposition (CVD) of SiC is used either to grow epitaxial layers at high growth rate and to facilitate homopolytypic growth on on-axis substrates or to g...

Evaluation of Fracture Stress for the SiC Layer of TRISO‐Coated Fuel Particles Using a Modified Crush Test Method

Fracture stress data for the chemical vapor deposition SiC coatings of tri‐isotropic carbon/silicon carbide‐coated fuel particles were obtained using a newly developed testing and evaluation method, and their relationship with microstructure was investigated. A crush testing technique using a blanket foil at load‐transferring contact has been developed for hemispherical shell SiC specimens based on finite element analysis results. The mean fracture stress varied with test material in the range of 330–650 MPa, and was linked to the combined characteristics of inner surface roughness and porosity.

Network model for the evolution of the pore structure of silicon-carbide membranes during their fabrication

A pore-network model is developed to study the evolution of the pore spce of a nanoporous silicon-carbide membrane during its fabrication by the chemical-vapor infiltration/chemical-vapor deposition (CVI/CVD) techniques. The pore space of the support is represented by a three-dimensional network of interconnected pores, in which the pores’ effective size is distributed according to a pore size distribution (PSD) that closely mimics the experimental PSD. The chemical reaction that generates the SiC, the various transport mechanisms in the pores, and the evolution of the pore structure during the SiC deposition on the pores’ surface are included in the model. The Maxwell–Stefan equations are used for describing the pore-level transport processes, which include the Knudsen and hindered diffusion, as well as viscous flow. The effect of pore shrinkage and blockage as a result of the deposition of the SiC on the pores’ internal surface is taken into account. The simulator monitors the PSD as the membrane's structure develops by the CVD process and evolves. Also computed are the permeances of argon, the carrier gas, and of helium during the CVD, as well as the membrane's selectivity. Good agreement is found between the simulation results and the experimental data. Thus, the model may be used for determining the optimal conditions under which a membrane may achieve a given value of permselectivity.

Fabrication of a multi-layered carbon nanotube/SiC stack structure

A multi-layered carbon nanotube (CNT)/SiC stack structure was fabricated by repeated alternate deposition and surface decomposition of SiC. The newly deposited 3C-SiC layer on the CNT film had good crystallinity; the CNTs produced by the decomposition of the 3C-SiC were as mostly aligned as the CNTs produced from pristine 6H-SiC. By appropriate choice of deposition and decomposition conditions we demonstrated that it is possible to produce alternating CNT and SiC layers with a controlled thickness.

Synthesis and characterization of 4H-SiC on C-plane sapphire by C 60 and Si molecular beam epitaxy

4H-SiC (silicon carbide) films were grown on (0001) sapphire substrate at rather low temperatures(1000–1100 °C) with relative high deposition rate by using fullerene (C 60) and silicon solid sources molecular beam epitaxy with substrate nitridation and aluminum nitride (AlN) buffer layer deposition prior to the SiC deposition. The effects of substrate nitridation and AlN buffer layer to the adhesion of the SiC thin films on sapphire have been studied. X-Ray diffraction, pole figure, atomic force microscope, Fourier transform infrared spectroscopy and photoluminescence were employed for the analysis of composition, orientation of the film and surface morphology. Relative high deposition rate at ∼ 165 nm/h was achieved.

Thermal plasma CVD and wear resistance of double layered Ti–Si–B–C/Ti–B–C coatings on WC–Co cutting tools with various roughness

The double-layer deposition of composite SiC–TiBC (Ti–Si–B–C) films with various Si contents (0, 40, 55, 60 and 100 mol%) on Ti–B–C was achieved from mixtures of titanium tetra-ethoxide, boron tri-ethoxide, and/or hexa-methyl-disiloxane solutions at about 700 °C on WC–Co cutting tools by Ar/H 2 thermal plasma CVD. The crystalline phases of TiB 2, TiC, and SiC were identified in the coatings by thin film grazing incidence X-ray diffraction. The surfaces and cross-sections of the double-layer coatings were observed by scanning electron microscopy to reveal their microstructure. Cutting tests of the double-layer Ti–Si–B–C/Ti–B–C were carried out by determining the flank and crater wear. The wear rate of the double-layer formed with the Ti–Si–B–C composite over-layer with 55 mol% Si was the slowest of the five samples. In addition, the effect of surface roughnesses (Ra (μm) = 0.03, 0.20 and 0.55) on the coating and wear resistance of the double-layer Ti–Si–B–C/Ti–B–C with 55 mol% Si was investigated by cross-sectional SEM observation and cutting tests.