SiC Interlayer Research Articles

Microstructural evolution of diamond thin film grown on a silicon substrate via a surface-wave plasma system: Identification of intermediated phase

Diamond thin films are promising for diverse applications because of their exceptional properties. Understanding the interface between diamond films and substrates is crucial for optimizing the film quality and functionality. In this study, a diamond thin film was grown on a Si(100) substrate using a microwave-based surface-wave plasma system and subjected to transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS). The formation of a SiC interlayer was identified at the interface between the diamond thin film and Si substrate through cross-sectional TEM and EELS. Analysis of the atomic structure and crystalline properties indicated that the interlayer was β-SiC and that the orientation relationships [110]β-SiC//[110]Si and (111)β-SiC//(111)Si existed at the β-SiC/Si interface. The β-SiC interlayer exhibited the {111} extra half-planes, because they were more easily formed by the {111} planes than the {110} extra half-planes generated on {001} planes through 60° misfit dislocations. Many stacking faults and microtwins were observed in the diamond grains; such planar defects were likely attributed to strain behavior and complex contrasts at the nanoscale.

Anti-ablation performance of plasma sprayed ZrB2/SiC coatings on C/C substrates and the influence of a chemical vapor deposited SiC interlayer

To address the industrial usage of carbon/carbon (C/C) substrates with plasma-sprayed ZrB2/SiC coatings, a continuous and dense chemical vapor deposition (CVD)-SiC interlayer of 150 µm was deposited on a C/C substrate. The integration of CVD-SiC with the C/C substrate and plasma sprayed (PS) ZrB2/SiC coatings results in a tight interface. The SiC interlayer significantly reducing thermal stress in the optimized composites up to 1828 Mpa, a decrease of approximately 60% compared to standard composites without CVD-SiC. Ablation tests conducted showed that the optimized composite displayed remarkable mass ablation rate of − 11.7% after ablation for 600 s, with a notable increase of − 3.5% even after ablation for 1800 s. After 600 s of ablation, the exposed SiO2 layer is approximately 500 µm in size. After 900 s of ablation, the exposed SiO2 layer is approximately 1500 µm. After 1800 s of ablation, the SiO2 is completely evaporated, exposing the C/C matrix, at which point the coating has failed. The SiC interlayer improve the ablation resistance due to the continuous SiO2 film formed by the self-sealing and O anti-diffusive properties.

Interaction study of molten uranium with multilayer SiC/Y2O3 and Mo/Y2O3 coated graphite

Graphite crucibles are used for melting uranium and its alloys in VIM furnace. Various coating materials namely Al2O3, ZrO2, MgO etc. are applied on the inner surface of the crucibles using paint brush or thermal spray technique to mitigate U-C interaction. These leads to significant amount of carbon pick-up in uranium. In this study, the attempts are made to develop multilayer coatings comprising of SiC/Y2O3 and Mo/Y2O3 on graphite to study the feasibility of minimizing U-C interaction. The parameters are optimized to prepare SiC coating of about 70μm thickness using CVD technique on graphite coupons and subsequently Y2O3 coating of about 250μm thickness using plasma spray technique. Molybdenum and Y2O3 layers were deposited using plasma spray technique with 70μm and 250μm thickness, respectively. Interaction studies of the coated graphite with molten uranium at 1450°C for 20 min revealed that Y2O3 coating with SiC interlayer provides physical barrier for uranium-graphite interaction, however, this led to the physical separation of coating layer. Y2O3 coating with Mo interlayer provided superior barrier effect showing no degradation and the coatings remained intact after interaction tests. Therefore, the Mo/Y2O3 coating was found to be a promising solution for minimizing carbon pick-up during uranium/uranium alloy melting.

Thermal shock resistance enhancement by improved interfacial bonding for carbon/aluminium composites

Carbon/aluminium (C/Al) composites have the advantages of low density and high electrical conductivity, which have potential applications in aerospace, rail transportation and other fields. However, the unstable bonding of the C/Al interface and significant thermal expansion differences have resulted in risks of the composites' failure once suffering from severe thermal shock. In this work, the C/Al composites were prepared by the pressure impregnation method, and silicon (Si) was added to overcome the problems of C/Al non-wettability and thermal expansion differences. The effects of mass fractions of doped silicon on the mechanical properties, electrical conductivity and thermal shock resistance of C/Al composites were also examined. Results show that the formed SiC interlayer has effectively enhanced the interfacial bonding and reduced the differences in the thermal expansion coefficient of each component. As a result, the thermal shock resistance of the composites has been remarkably improved, and the flexural strength could remain 90% of the original level after the thermal shock test, compared with 50% of that without Si doping.

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.

Controllable distribution of reinforcements for reducing the strain energy in dissimilar ceramic/metal joints

A novel design of a multi-layered joint architecture, characterized by the controllable spatial distribution of ceramic reinforcements, was obtained, when brazing ZrB2-SiC ceramics and Ti-6Al-4 V reinforced by TiB whiskers with AgCu filler. To induce SiC reinforcements to cluster together, within the center of the filler and especially away from the ZrB2-SiC, SiC was added into joint, in the form of a SiC interlayer featuring a 3D-bridged network structure with continuous micro-channels infiltrated by capillary force by liquid filler during brazing. Different SiC particles were connected together, by micro-bridges being not destroyed during brazing. The layer rich in SiC could reduce thermal expansion mismatch between different substrates, the AgCu next to the ZrB2-SiC could relax the strain energy by high plastic deformation. Compared to joint brazed with single AgCu, joint strain energy decreased from 10.8 × 10−6 J to 8.6 × 10−6 J, accordingly joint shear strength increased from ∼5.4 MPa to ∼41.2 MPa.

Effect of SiC content and interlayer difference on microstructural characterization and mechanical properties of functionally graded 6061Al/SiCp composites

Metal matrix composite reinforced gradiently by ceramic phase is a new type of high-tech material with broad application prospects, and the study of the effect of SiC content and interlayer difference on functionally graded materials (FGMs) is vital for the guiding significance of the practical application. Functionally graded 6061Al/SiCp composites (6061Al/SiCp FGMs) were prepared by hot pressing sintering herein, and mechanical properties were evaluated by tensile tests conducted under different temperatures. 6061Al/SiCp FGMs were observed under optical microscopy to identify the particle distribution and transition status between layers, and fracture surfaces were observed to verify the detailed fracture mechanisms. Results show that 6061Al/SiCp FGMs achieving high relative densities of more than 0.99 satisfy requirements of microstructure. When the interlayer difference is consistent, the tensile strength of FGMs increases as the SiC content increases in each layer constituting FGMs, and FGMs have the highest tensile strength at room temperature. The elongation of FGMs decreases as the SiC content increases in each layer constituting FGMs, and FGMs have the highest elongation at 100 °C. When the intermediate layer is consistent, the tensile strength of FGMs with a lower interlayer difference is better, which can be attributed to the interaction of elongation and dislocation.

Interface design to tune stress distribution for high performance diamond/silicon carbide coated cemented carbide tools

The stress distribution of the interface plays a key role in adhesion and performances of diamond coated tools. Herein, we report a combined simulation and experimental strategy to significantly minimize the thermal stress by interface design in the diamond/SiC architectures. Different diamond/SiC films, including pure diamond, composite, single SiC interlayer, gradient interlayer and multilayer, were simulated by finite element analysis and synthesized on cemented carbide tools by hot filament chemical vapor deposition (HFCVD). The stress distribution was tailored over the diamond/SiC architecture, and the maximum stress value at the cutting edge was best suppressed for the composite (58% reduction) and the gradient film (49% reduction), which resulted in the best film adhesion and were sufficient for cutting performances. The pure diamond surface ending on the gradient coated tool allowed for non-sticking machining Al-13 wt% Si alloy, resulting in enhanced workpiece quality and extended tool lifetime. Its tool lifetime was at least 7 times longer than that of the pure diamond film, and at least 4 times longer than a commercial diamond coated end mill. The diamond/SiC architectures represent a potent solution for adherent diamond coated tools with excellent machining performances.

Sequential-template synthesis of hollowed carbon polyhedron@SiC@Si for lithium-ion battery with high capacity and electrochemical stability

In this work, we propose a sequential-template method to synthesize hollowed carbon polyhedron@silicon carbide@silicon (HCP@SiC@Si) tandem architecture as high-performance lithium ion batteries’ (LIBs) anode. The ZIF-8@SiO2 Yolk-shell precursor is prepared by the in-situ synthesis of SiO2 film on ZIF-8 where ZIF-8 is etched by Si(OH)4 simultaneously, and the following magnesium thermal reduction treatment results in the formation of HCP@SiC@Si. The HCP@SiC@Si is composed of a carbon inner-shell, SiC interlayer and Si nanoflakes outer-layer, realizing a novel nanostructure. As a result, the HCP@SiC@Si anode with highly-crystalized SiC interlayer exhibits good initial discharge capacity of 748.2 mAh g−1 with Coulombic efficiency of 98.06% at the current density of 0.1 A g−1. Further, the reversible capacity tends to stabilize at 816.3 mAh g−1 after 100 cycles. Even the current density reaches to 1.0 A g−1, a highly reversible capacity of 218 mAh g−1 after 200 cycles can be achieved. Beyond that, the structure of HCP@SiC@Si maintains very well after withstanding long cycling. These results suggest that this tandem structure promotes the kinetics for lithiation/de-lithiation and diffusion process. Meanwhile, the significance of SiC with high crystallinity on the improved LIB’s performance of HCP@SiC@Si is highlighted as well.

Improved corrosion resistance of hydroxyapatite coating on carbon fiber by applying SiC interlayer

A hydroxyapatite (HA, Ca10(PO4)6(OH)2) coating is successfully fabricated on carbon fiber (CF) with SiC interlayer prepared via pack cementation method at 1773 K, 1873 K, 2073 K and 2273 K. The morphologies and microstructures of the SiC interlayer and HA coating are analyzed. The corrosion performance is evaluated by electrochemical behavior in simulated body fluid (SBF). The results show that the morphologies and crystalline structures of SiC interlayers vary with temperatures. The SiC interlayer improves the surface wettability for CF. The HA coating deposited on SiC interlayer modified CF exhibits denser and more uniform structure than that on the CF. Corrosion test shows that the corrosion potential (Ecorr) and corrosion current density (Icorr) for HA coated CF with SiC interlayer are −0.13 V and 0.64 × 10−5 A/cm2, respectively. For HA coated CF, the Ecorr and Icorr are −0.15 V and 1.25 × 10−5 A/cm2, respectively. The Ecorr increases and the Icorr decreases resulting from the introduction of SiC interlayer. The corrosion resistance of HA coated CF with SiC interlayer in SBF is better than that of HA coated CF. The HA coated CF with SiC interlayer would be possible for biological application.

Surface optimization of CVD grown silicon carbide interlayer on graphite for plasma sprayed yttria topcoat

Chemical Vapor Deposition (CVD) technique is employed to deposit uniform, smooth, and dense SiC interlayer over High-Density Graphite (HDG) substrate, as an interlayer for subsequent deposition of yttria (Y2O3) topcoat by Atmospheric Plasma Spray (APS) process. In any thermal spray process, since the bonding is purely mechanical interlocking, the surface roughening of smooth CVD grown SiC surface becomes essential. Different surface preparation techniques like alumina grit blasting, plasma etching, laser ablation, and chemical etching were attempted to create rough anchoring patterns on SiC surface. Chemical etching of SiC interlayer by using molten eutectic NaOH/KOH is found to be effective in introducing the desire anchoring sites for Y2O3 splats during plasma spraying. The microstructural features and surface roughness of CVD grown SiC and after subsequent surface roughening treatments were compared using SEM/EDS and profilometer, respectively. The performance and its durability evaluation were carried out by thermal cycling studies on Y2O3 coated samples with and without SiC interlayer at 1723 and 1823 K that shows considerable improvement in the life of plasma sprayed Y2O3 coating with SiC interlayer.

Temperature effect on Al predose and AlN nucleation affecting the buffer layer performance for the GaN-on-Si based high-voltage devices

An AlN buffer layer allows epitaxial growth of GaN on silicon substrates. We have studied the early AlN nucleation stage performed at high and low process temperatures. We show that the temperature has a crucial effect on the chemical reactions on the Si substrate during the initial growth stage. We have observed that large clustered defects are formed at 1000 °C. These defects are responsible for degradation of the vertical leakage current (VLC) blocking capability of the buffer layer. Formation of the defects is prevented if the temperature is lowered to 800 °C, which is explained by a carbonization of the Si surface. Formation of the SiC interlayer leads to the stable AlN/Si(111) interface during subsequent high-temperature growth of the buffer structure. We demonstrate that very low VLCs in superlattice-based buffer are achieved using the low-temperature nucleation process, which makes it suitable for fabrication of high voltage AlGaN/GaN high electron mobility transistor devices.

Structural optimization and quantum size effect of Si-nanocrystals in SiC interlayer fabricated with bio-template

Amorphous SiC/Si multilayers were fabricated using alternately magnetron sputtering of SiC and electron beam evaporation of Si targets. The as-deposited films were annealed at different temperatures from 800 till 1000 °C to form Si-nanocrystals (Si-NCs) and study the layered structural stability by different analytical techniques, including x-ray reflectivity (XRR), x-ray diffraction (XRD), secondary ion mass spectroscopy (SIMS), transmission electron microscopy (TEM), and surface morphology by atomic force microscopy (AFM). XRR demonstrated that SiC/Si multilayers annealed at temperatures up to 1000 °C retain their layered structure. XRD and TEM confirmed the formation of Si-NCs after annealing at ≥800 °C. The Si-NCs size estimated from the TEM images is ∼4 nm for the multilayered sample with alternating 2 nm SiC and 4 nm Si layers. SIMS revealed that SiC/Si multilayers annealed at 800 °C possess the best periodic structure possibly due to the lowest carbon interdiffusion as compared to the samples annealed at higher temperatures. AFM micrograph confirmed that SiC/Si multilayers annealed at 800 °C characterized by the lowest surface roughness having RMS value of 0.123 nm as compared to the samples annealed at 900 °C and 1000 °C having RMS values of 0.207 and 0.530 nm, respectively. Size-controlled 3D array of Si-NCs separated by SiC barriers was fabricated by neutral beam etching of annealed SiC/Si multilayers with different Si layers thickness from 2 to 6 nm using a bio-template consisting of ferritin molecules. The size-dependent band gap energy of Si-NCs was estimated by optical spectroscopy to vary from 1.61 till 1.92 eV owing to the quantum confinement effect as the Si-NCs size decreases, which is appropriate for application in Si-based tandem solar cells.

Effects of random chopped short carbon fibers on microstructure and mechanical properties of joints for Cf/SiC composites by reaction bonding process

Random chopped short carbon fibers (Csf)/phenol-formaldehyde resin (PF)/SiC powder mixtures are used as filler for the joining of Cf/SiC composites to obtain SiC interlayer at the joining region. The influences of Csf on the microstructure and mechanical properties have been investigated. Research shows that the introduction of Csf can improve the microstructure uniformity of the joint and reduce residual silicon content in the interlayer. The joint achieve a high flexural strength of 232 ± 33 MPa as the carbon fiber content is 30 wt.%, which is similar to that of the Cf/SiC composites (220 ± 21 MPa). The decrease in residual silicon content and the formation of nano-sized SiC particles are the main reasons for high joining strength.

Pack cemented silicon carbide interlayer for plasma sprayed yttria over graphite

ABSTRACTThermodynamically stable and non-reactive yttrium oxide is proposed to be the coating material on high-density graphite (HDG) crucible for melting and consolidating uranium in the pyrochemical reprocessing of spent metallic nuclear fuels. Yttria deposited over HDG by atmospheric plasma spray (APS) process without interlayer cannot withstand temperatures above 1400°C because of large thermal expansion mismatch and high-temperature partial oxidation of underlying graphite substrate through pores and openings in the plasma sprayed yttria layer. To overcome this limitation, a stable oxidation-protective intermediate layer of SiC was developed over graphite by conventional pack cementation process using two different precursor powders. The coated samples were characterized with respect to coating thickness, microstructure, and phase composition. Experimental results revealed that the optimum pack composition for obtaining thick and diffused coating was 70 wt. % Si – 20 wt. % C – 10 wt. % Al2O3. Subsequently, yttria top coat was deposited over pack cemented HDG coupons by APS process with optimized process parameters. The interlayer of SiC developed by pack cementation for yttria top coat facilitated to extend the thermal cycling life of the coating in inert argon environment significantly. The onset of micro-cracking in the top coat with SiC interlayer occurred after 45, 25 and 13 thermal cycles at 1400°C, 1450°C and 1500°C, respectively.

Molten Salt Corrosion Resistance of Yttria Stabilized Zirconia Coating with Silicon Carbide Interlayer on High Density Graphite

The high temperature corrosion behaviour of yttria stabilized zirconia (YSZ) coated high density graphite (HDG) with and without SiC interlayer was evaluated in LiCl–KCl molten salt at 600 °C. The YSZ coated HDG samples without interlayer were tested for 50, 250, 1000 and 2000 h and the YSZ coated HDG samples with SiC interlayer were studied for 50, 500, 2000 and 3500 h durations. Characterisation of the corrosion tested samples revealed no delamination or failure of the YSZ coating in both the cases, and insignificant weight gain was observed in all the tested samples in the molten salt. The lamellar morphology of the plasma spray coating was intact even after exposure to molten salt for long duration, implying no corrosion attack of the coating and HDG in the molten salt. SEM cross-section examination confirmed neither coating degradation, nor penetration of molten salt into the HDG substrate. X-ray diffraction and Laser Raman spectroscopic analyses ascertained that no phase change occurred in YSZ after the long exposure in molten salt. Present study confirmed the phase stability and durability of YSZ coating in providing corrosion resistance and protection to HDG for high-temperature molten salt applications.

Deposition of a Diamond-Like-Carbon Film by Ion Plating and Investigation on its Adhesiveness

Diamond-like-carbon (DLC) films are promising as coating materials. Ion plating, an excellent method in terms of adhesiveness, step coverage, and deposition rate, can form not only pure metal films but also oxide films, nitride films, and carbonized films. In this study, which aimed to form a DLC film with good adhesiveness and a diamond crystal structure, a DLC film, with a SiC interlayer formed by ion plating with introduction of tetramethylsilane (TMS), was formed. It was experimentally revealed that as the interlayer thickness increases, the crystal structure in the DLC film becomes more diamond rich, and the adhesiveness of the DLC film and substrate is thereby improved.

Enhancement in the rate of the top seeded solution growth of SiC crystals via a roughening of the graphite surface

With the top seeded solution growth (TSSG) method, SiC crystals are grown in a Si–C solution where the dissolved C is supplied from graphite crucibles. In this study, the reactivity of the graphite was enhanced by roughening the surface to form a SiC interlayer, the intermediate compound in the dissolution of C to a Si melt. As a result, we clearly observed an enhancement in the growth rate by roughening the graphite surface in the crystal growth of SiC using TSSG method.

Crystallinity control of SiC grown on Si by sputtering method

We investigated a method of controlling the crystallinity of an n-type SiC (n-SiC) layer grown on a p-type 4°-off-axis Si(111) (p-Si) substrate by our sputtering method for use as SiC/Si devices. An n-SiC layer grown on p-Si at 810°C exhibits columnar 3C-SiC(111) crystal growth. However, it contains many defects near the n-SiC/p-Si interface. We then propose a method in which a 10-nm-thick nondoped SiC (i-SiC) interlayer is grown at a low temperature of 640°C prior to the growth of the n-SiC layer at 810°C, which results in a decrease in the number of defects at the SiC/p-Si interface and an intensive increase in the crystallinity of the n-SiC, compared with that of n-SiC grown at 810°C without the interlayer, probably via effective interlayer reconstruction and an enhancement in the crystallinity of the i-SiC interlayer itself during the n-SiC growth. Furthermore, the n-SiC/i-SiC-interlayer/p-Si structure was applied as a Si-based solar cell and the energy conversion efficiency of the n-SiC/p-Si solar cell effectively increased with the insertion of the i-SiC interlayer.

The role of an SiC interlayer at a graphite–silicon liquid interface in the solution growth of SiC crystals

SiC crystal growth using the top seeded solution growth (TSSG) method involves the precipitation of solid SiC from carbon that is dissolved in a silicon melt. The growth rate of SiC is strongly influenced by the solubility of C in liquid Si, which is quite low. In this study, the dissolution of C from graphite to the Si melt was explored by observing the formation of an SiC interlayer at a graphite – Si liquid interface. The SiC interlayer was observed to become thickened during the several hours needed to reach a certain thickness at 1500°C. Assuming that the SiC interlayer is a direct C source, a pre-formed SiC layer was coated on the graphite crucible to evaluate its effect on the concentration of C in the Si melt. As a result, the concentration of C in the Si melt increased within a short time, especially at low temperatures. By applying the SiC coated crucible to the TSSG process for SiC crystal growth, we confirmed that the development of a pre-formed SiC layer enhanced the growth rate of SiC crystals, especially at the initial stage of crystal growth at low temperatures.