SiC Shell Research Articles

Influence of microwave sintering temperatures on mechanical and microstructural Behavior of Al/SiC/snail shell hybrid composite synthesized through powder metallurgy technique

This study emphasizes the synthesis of hybrid aluminum composite reinforced with SiC and Snail Shell (S-Shell) particles through the powder metallurgy technique. The hybrid composite corresponding to the optimized volume fraction of SiC and Snail shell powder (Al-6%SiC-6%S-Shell) was subjected to microwave-assisted sintering (MAS) by varying the sintering temperatures from 400°C to 550°C in steps of 50°C. Results concluded that microwave-sintered composites show superior mechanical characteristics than the composites sintered through conventional sintering techniques. The maximum ultimate tensile strength (U.T.S) of 316 MPa, and compression strength of 396 MPa were obtained for microwave sintered Al-6%SiC-6%Snail shell powder composite sintered at 500°C. However, increasing the sintering temperature above 500°C leads to a reduction in U.T.S and Compression strength due to the formation of coarse grains by absorbing the microwaves at higher temperatures. The U.T.S, Compression strength and Vickers hardness of the microwave sintered Al-6%SiC-6%Snail shell powder hybrid composite sintered at 500°C was enhanced by 42.08%, 42.4%, and 35.5% compared to conventionally sintered hybrid composite. The grain size was found to be increased with an increase in microwave sintering temperature due to the enhancement in the absorption capability of the microwaves with the temperature rise. The results of this study also suggest that choosing materials with a high microwave response helps to achieve improved mechanical properties for microwave-sintered composites.

Enhancement of vibrational performance and corrosion behavior of hybrid AMC fabricated from aluminum alloy wheel scrap reinforced with SiC and snail shell particles via vortex casting

Enhancement of vibrational performance and corrosion behavior of hybrid AMC fabricated from aluminum alloy wheel scrap reinforced with SiC and snail shell particles via vortex casting

The utilisation of coconut shell ash in production of hybrid composite: Microstructural characterisation and performance analysis

Agriculture waste-reinforced hybrid metal matrix composites (HMMCs) have developed as a potentially green, productive, economical, and ideal replacement for particle-reinforced composites. A number of industries, including aerospace, automotive, and packaging, have demonstrated a keen interest in the development of new and innovative composites in a sustainable manner, is bio-waste particulate reinforced composite. The effect of reinforcements is investigated in the current research work, which employs the ultrasonic stir casting method with SiC (ranging from 3 to 9% by weight) and coconut shell ash (5% by weight in equal proportion) as reinforcement along with the aluminium matrix. With the two-stage ultrasonic stir casting process, the distribution of reinforcement in the aluminium matrix is ensured to be uniform. The microstructure evolution, mechanical and tribological behaviours were also evaluated to ascertain the integrity of fabricated composites. The XRD analysis confirms the reinforcements and oxide layer formed on the specimen surface. Currently, the fabricated composite improves monolithic alloy in terms of hardness and tensile strength approximately by 60% and 66%, respectively, while reducing wear rate by 51%. The nanoindentation investigation implies that the composites that have been developed have improved nanomechanical properties. Overall, using CSA along with SiC in HMMCs could be a potential product to reduce the usage of synthetic fiber and application design for economical products.

Experimental investigation on stir casted hybrid composite AA7068 with SiC and coconut shell fly ash

Hybrid aluminium matrix composites through stir casting were made and their mechanical properties are evaluated in this research paper. To strengthen Al7068 hybrid aluminium matrix composites with different SiC weight percentages were created using SiC (0, 2, 4, 6, and 8), coconut shell fly ash (4 wt%) and nano magnesium (2%). Hardness, Impact, ductility and Tensile Strength are just a few of the mechanical properties discussed in this work. Researchers found that adding eight percent SiC reinforcement to aluminium 7068 alloy reinforced with four percent coconut shell fly ash increased the composites' hardness through 32 percent. Adding six percent SiC and four percent coconut shell fly ash to an aluminium alloy 7068 increased its tensile strength by 65 percent. A combination of coconut shell fly ash with Silicon carbide reduced the ductility of the composite material. Aluminium alloy with CSFA and SiC increased the impact energy to 3.2 J. The impact strength increased and decreased in fabricated composites when reinforcement was added to base material.

In Situ Synthesis of Core-Shell-Structured SiCp Reinforcements in Aluminium Matrix Composites by Powder Metallurgy

SiCp reinforced aluminium matrix composites (AMCs), which are widely used in the aerospace, automotive, and electronic packaging fields along with others, are usually prepared by ex situ techniques. However, interfacial contamination and poor wettability of the ex situ techniques make further improvement in their comprehensive performance difficult. In this paper, SiCp reinforced AMCs with theoretical volume fractions of 15%, 20%, and 30% are prepared by powder metallurgy and in situ reaction via an Al-Si-C system. Moreover, a combined method of external addition and an in situ method is used to investigate the synergistic effect of ex situ and in situ SiCp on AMCs. SiC particles can be formed by an indirect reaction: 4Al + 3C → Al4C3 and Al4C3 + 3Si → 3SiC + 4Al. This reaction is mainly through the diffusion of Si, in which Si diffuses around Al4C3 and then reacts with Al4C3 to form SiCp. The in situ SiC particles have a smooth boundary, and the particle size is approximately 1–3 μm. A core-shell structure having good bonding with an aluminium matrix was generated, which consists of an ex situ SiC core and an in situ SiC shell with a thickness of 1–5 μm. The yield strength and ultimate tensile strength of in situ SiCp reinforced AMCs can be significantly increased with a constant ductility by adding 5% ex situ SiCp for Al-28Si-7C. The graphite particle size has a significant effect on the properties of the alloy. A criterion to determine whether Al4C3 is a complete reaction is achieved, and the forming mechanism of the core-shell structure is analysed.

Studies on Egg Shell and SiC Reinforced Hybrid Metal Matrix Composite for Tribological Applications

The hybrid metal matrix composite is developed through stir casting process. In theAl7075 aluminium matrix material, two different combination of reinforcements are used to make hybrid composite and they are as (i) Al7075 + Al2O3 + SiC and (ii) Al7075 + Al2O3 + egg shell powder. The weight proportion of SiC and egg shell powder varied to study the influence of reinforcement. To validate the hybrid composite developed, electron microscopic imaging, density and hardness measured. Maximum surface hardness of 197 Hv is observed in the composite with 6% egg shell powder. The presence organic egg shell is in the form of calcium oxide which is harder than carbide particle reinforced in the hybrid composite material. It has posse’s natural strength compared to synthetic material and with less in density.The density of egg shell is less compared to SiC and alumina particle reinforcement. Electron images and the corresponding spectroscopic results infer that the reinforcements are equal distributed in the volume of composite. While casting the egg shell has been found in the form of calcium oxide along with aluminium and oxide elements. Since, the composite has less density which is light in weight compared to alumina or silicon carbide. With respect to sliding wear behaviour, the hybrid composite with Sample 1 (3% SiC) and Sample 4 (6% egg shell) has good wear resistance. With increase in hard particle the wear mechanism is abrasion and metal loss trend found increasing. The minimum of 0.25 mm3/min found with less load (10 N) and 0.42 mm3/min for 20 N load. On prolonged exposure more than 40 μm reached for maximum load. Increase in hard particle reinforcement (6% Al2O3 + 6% SiC) has induced severe surface damage due to abrasion on worn surface. Adhesive morphology and minimum wear are noticed with 6% Al2O3 + 6% SiC in hybrid composite. Therefore, it is confirmed that the reduced in hard particle or increase in egg shell may produce expected results on sliding wear behaviour.

Enhanced mechanical and wear properties of Al6061 alloy nanocomposite reinforced by CNT-template-grown core\u2013shell CNT/SiC nanotubes

Novel one-dimensional template-grown coaxial SiC@carbon nanotubes (SiC@CNTs) were fabricated using a chemical vapor deposition method. To facilitate the formation of SiC on CNT template, a molecular-level mixing process was used to coat the surface of commercial multiwalled carbon nanotubes (MWCNTs) by Fe2O3. These Fe-CNTs were transformed into SiC@CNT nanotubes, which were then mixed with Al6061 alloy and consolidated by spark plasma sintering to obtain Al6061-SiC@CNT nanocomposites. The addition of 5 vol% SiC@CNT resulted in 58% enhancement in Young’s modulus and 46% enhancement in yield strength. Furthermore, the friction coefficient was reduced by 31% and the specific wear rate was reduced by 45%. The enhancement effect of Al6061-SiC@CNT on the mechanical and tribological properties was much greater than those of traditional nanoparticles, nanowires, and whiskers of SiCs. The extraordinary strengthening behavior of SiC@CNT, when compared with that of other SiC analogues, is attributed to the coaxial structure consisting of a SiC shell and CNT core. This coaxial structure enhanced the mechanical and tribological properties beyond that attainable with traditional SiC-derived reinforcements.

Development of SOI FETs Based on Core-Shell Si/SiC Nanowires for Sensing in Liquid Environments

Core–shell Si/SiC nanostructures appear as promising building blocks for sensing applications, thanks to the high chemical stability of SiC coupled with the semiconducting properties of Si. In order to optimize the fabrication process of such structures, Si nanowires were coated with a thin SiC layer, and integrated as back-gated field-effet transistors. Two approaches for the fabrication of the SiC shell were then investigated. The first approach involves chemical vapor deposition of amorphous SiC on Si nanowires, without the need for masking; the second approach involves carbonization of Si surfaces to produce a thin crystalline SiC layer, but requires a larger thermal budget. The resulting structures were analyzed using high-resolution transmission electron microscopy (HR-TEM), and the devices were characterized electrically. Electrical characterization shows that the carbonization approach induces a dramatic decrease in drain-to-source current associated with gate leakage, whereas the electrical performances were preserved in the case of chemical deposition.

Effect of hydrothermal corrosion on the fracture strength of SiC layer in tristructural‐isotropic fuel particles

AbstractThe hydrothermal corrosion behavior of SiC layer in tristructural‐isotropic (TRISO) fuel particles and its effect on the fracture strength were investigated. The corrosion test was performed using the static autoclave at 400°C/10.3 MPa. The SiC layer exhibited a thickness loss and the corrosion rate followed a linear law. During corrosion, carbon was formed on the SiC surface due to the loss of Si. The corrosion was found preferentially occurred at the grain boundary of SiC, leading to the grain detachment and pit formation. The rate determining step of the corrosion was SiO2 formation rather than SiO2 dissolution in the hydrothermal environment. The fracture strength of SiC shell after corrosion was evaluated using the crush test. It showed a slight decrease with an increase in corrosion time, due to the thickness reduction in SiC layer. The results of this study demonstrated that the SiC in TRISO particles has good corrosion resistance in the hydrothermal environment.

Solid-State Limited Nucleation of NiSi/SiC Core-Shell Nanowires by Hot-Wire Chemical Vapor Deposition.

This work demonstrated a growth of well-aligned NiSi/SiC core-shell nanowires by a one-step process of hot-wire chemical vapor deposition on Ni-coated crystal silicon substrates at different thicknesses. The NiSi nanoparticles (60 to 207 nm) acted as nano-templates to initially inducing the growth of these core-shell nanowires. These core-shell nanowires were structured by single crystalline NiSi and amorphous SiC as the cores and shells of the nanowires, respectively. It is proposed that the precipitation of the NiSi/SiC are followed according to the nucleation limited silicide reaction and the surface-migration respectively for these core-shell nanowires. The electrical performance of the grown NiSi/SiC core-shell nanowires was characterized by the conducting AFM and it is found that the measured conductivities of the nanowires were higher than the reported works that might be enhanced by SiC shell layer on NiSi nanowires. The high conductivity of NiSi/SiC core-shell nanowires could potentially improve the electrical performance of the nanowires-based devices for harsh environment applications such as field effect transistors, field emitters, space sensors, and electrochemical devices.

Microstructure and mechanical property of Cf/SiC core/shell composite fabricated by direct ink writing

A novel approach for the fabrication of Short carbon fibers reinforced SiC ceramic composites filaments with core-shell microstructure by direct ink writing was firstly proposed. A novel core-shell feed rod for co-extrusion was designed. Fiber interface layer was prepared by precursor infiltration pyrolysis with polycarbosilane. The results indicated that the ratio (d/D) of carbon fiber (core) to SiC (shell) could be controlled effectively. The debonding and fracture of short fibers with high orientation might improve the fracture resistance of the Cf/SiC composite. The filament-based specimens with strength of ~123 MPa and porosity of ~31% (d/D = 0.6) were successfully fabricated.

Rapid microwave synthesis of coaxial SiC/carbon fibre (SiC/CF) with improved oxidation resistance and wettability

Coaxial SiC/carbon fibre (SiC/CF) materials were prepared via rapid microwave synthesis at 1400 °C for 30 min. X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis were performed to investigate the structure and oxidation resistance of the samples. The results showed that a uniform and continuous β-SiC shell was obtained after the oxidation, confirming that the SiC/CF samples had a coaxial structure. The shell thickness could be regulated by adjusting the Si:C molar ratio. The SiC shell improved the oxidation resistance of the CFs significantly. The surface wettability of SiC/CF was also investigated. It was found that the hydrophilic and rough SiC shell played an important role in enhancing the wettability of the CFs.

Depositing thin SiC shells to weld chopped SiC fibers as ultralight highly preamble porous combustion media

This article reports an ultralight highly permeable combustion medium for many gas-fired applications where more combustion efficiency, smaller thermal inertia and less structural size are urgently required. Chopped SiC fiber papers were prepared and then formed into mat structures. Then they were coated with SiC shells to weld the fibers at points of contact, resulting in rigid fiber porous media (FPM) with light and thin characteristics. Different SiC shell thicknesses were deposited to optimize the overall performance influenced by permeability, thermal physical properties and combustion performance. It was found that two types of pore structures existed in the FPM, the smaller pores near the lap joints and the larger pores away from the lap joints, leading to high permeability. The FPM with 3.0 µm SiC shell thickness, can achieve the relatively ideal combustion effect, with less CO and only 13 ppm NOx in the flue gas. The increase of SiC shell thickness will slightly decrease the porosity and permeability, but it is conducive to improve the structural stability under gas blowing environment at high temperature. The thin SiC shell welded FPM are of great potential to improve the combustion efficiency and prolong service life due to their exceptional ultralight highly preamble characteristics.

Local atomic structure of Pd and Ag in the SiC containment layer of TRISO fuel particles fissioned to 20% burn-up

The structure and speciation of fission products within the SiC barrier layer of tristructural-isotropic (TRISO) fuel particles irradiated to 19.6% fissions per initial metal atom (FIMA) burnup in the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL) was investigated. As-irradiated fuel particles, as well as those subjected to simulated accident scenarios, were examined. The TRISO particles were characterized using synchrotron X-ray absorption fine-structure spectroscopy (XAFS) at the Materials Research Collaborative Access Team (MRCAT) beamline at the Advanced Photon Source. The TRISO particles were produced at Oak Ridge National Laboratory under the Advanced Gas Reactor Fuel Development and Qualification Program and sent to the ATR for irradiation. XAFS measurements on the palladium and silver K-edges were collected using the MRCAT undulator beamline. Analysis of the Pd edge indicated the formation of palladium silicides of the form PdxSi (2 ≤ x ≤ 3). In contrast, Ag was found to be metallic within the SiC shell safety tested to 1700 °C. To the best of our knowledge, this is the first result demonstrating metallic bonding of silver from fissioned samples. Knowledge of these reaction pathways will allow for better simulations of radionuclide transport in the various coating layers of TRISO fuels for next generation nuclear reactors. They may also suggest different ways to modify TRISO particles to improve their fuel performance and to mitigate potential fission product release under both normal operation and accident conditions.

Processing of alnico permanent magnets by advanced directional solidification methods

Advanced directional solidification methods have been used to produce large (>15cm length) castings of Alnico permanent magnets with highly oriented columnar microstructures. In combination with subsequent thermomagnetic and draw thermal treatment, this method was used to enable the high coercivity, high-Titanium Alnico composition of 39% Co, 29.5% Fe, 14% Ni, 7.5% Ti, 7% Al, 3% Cu (wt%) to have an intrinsic coercivity (Hci) of 2.0kOe, a remanence (Br) of 10.2kG, and an energy product (BH)max of 10.9MGOe. These properties compare favorably to typical properties for the commercial Alnico 9. Directional solidification of higher Ti compositions yielded anisotropic columnar grained microstructures if high heat extraction rates through the mold surface of at least 200kW/m2 were attained. This was achieved through the use of a thin walled (5mm thick) high thermal conductivity SiC shell mold extracted from a molten Sn bath at a withdrawal rate of at least 200mm/h. However, higher Ti compositions did not result in further increases in magnet performance. Images of the microstructures collected by scanning electron microscopy (SEM) reveal a majority α phase with inclusions of secondary αγ phase. Transmission electron microscopy (TEM) reveals that the α phase has a spinodally decomposed microstructure of FeCo-rich needles in a NiAl-rich matrix. In the 7.5% Ti composition the diameter distribution of the FeCo needles was bimodal with the majority having diameters of approximately 50nm with a small fraction having diameters of approximately 10nm. The needles formed a mosaic pattern and were elongated along one 〈001〉 crystal direction (parallel to the field used during magnetic annealing). Cu precipitates were observed between the needles. Regions of abnormal spinodal morphology appeared to correlate with secondary phase precipitates. The presence of these abnormalities did not prevent the material from displaying superior magnetic properties in the 7.5% Ti composition. Higher Ti compositions did not display the preferred spinodal microstructure, explaining their inferior magnetic properties.

Fracture strength and principal stress fields during crush testing of the SiC layer in TRISO-coated fuel particles

Diametrical compression testing is an important technique to evaluate fracture properties of the SiC layer in TRISO-coated nuclear fuel particles. This study was conducted to expand the understanding and improve the methodology of the test. An analytic solution and multiple FEA models are used to determine the development of the principal stress fields in the SiC shell during a crush test. An ideal fracture condition where the diametrical compression test best mimics in-service internal pressurization conditions was discovered. For a small set of empirical data points, results from different analysis methodologies were input to an iterative Weibull equation set to determine characteristic strength (332.9 MPa) and Weibull modulus (3.80). These results correlate well with published research. It is shown that SiC shell asphericity is currently the limiting factor of greatest concern to obtaining repeatable results. Improvements to the FEA are the only apparent method for incorporating asphericity and improving accuracy.

Influences of hydrogen dilution on the growth of Si-based core–shell nanowires by HWCVD, and their structure and optical properties

Si-based core–shell nanowires were grown on Ni-coated crystal silicon substrates using a hot-wire chemical vapor deposition technique. The NiSi nanoparticles acted as catalysts that facilitated the growth of the core–shell nanowires without any hydrogen dilution as well as that ranging from 20 to 99 %. These nanowires were structured by single-crystalline NiSi cores and amorphous shells with consisting of nanocrystallites embedded within an amorphous matrix. Raman results reveal crystallization of amorphous Si to crystalline Si up to the crystalline volume fraction of 92.3 % for the nanowires grown with hydrogen dilution. An increase in hydrogen dilution enhanced the decomposition rate and the gas-phase reactions for SiC shell formation, while further increases up to 99 % suppressed the growth of the nanowires. Moreover, a phased transition from Si to SiC occurred with increases in hydrogen dilution above 20 %. The nanowires demonstrated superior optical absorption in the visible region, revealing their significant light-trapping ability. This paper discusses the influences of hydrogen dilution on the structure and optical properties of these core–shell nanowires.

Shell-Thickness Controlled Semiconductor-Metal Transition in Si-SiC Core-Shell Nanowires.

We study Si-SiC core-shell nanowires by means of electronic structure first-principles calculations. We show that the strain induced by the growth of a lattice-mismatched SiC shell can drive a semiconductor-metal transition, which in the case of ultrathin Si cores is already observed for shells of more than one monolayer. Core-shell nanowires with thicker cores, however, remain semiconducting even when four SiC monolayers are grown, paving the way to versatile, biocompatible nanowire-based sensors.

Effects of substrate temperature on the growth, structural and optical properties of NiSi/SiC core–shell nanowires

In this paper we attempt to study the growth of NiSi/SiC core–shell nanowires on Ni-coated glass substrates by hot-wire chemical vapor deposition. The samples were prepared at different substrate temperatures of between 350 and 527°C to investigate the growth of the nanowires. Ni nanoparticles were used as templates for initially inducing the growth of these core–shell nanowires at substrate temperature as low as 350°C. The high density of the nanowires was clearly demonstrated at higher substrate temperatures of 450 and 527°C. These core–shell nanowires were structured by single crystalline NiSi and amorphous SiC as the core and shell of the nanowires respectively. The amorphous SiC shell consisted of SiC nanocolumns within an amorphous matrix. The formation of these high density nanowires showed a noticeable suppression in photoluminescence emissions from the oxygen-related defects and superior optical absorption in visible and limited near infrared regions. The effects of substrate temperatures on growth, optical and structural properties of the nanowires are presented and discussed.

A low cost preparation of C/SiC composites by infiltrating molten Si into gelcasted pure porous carbon preform

C/SiC composites were prepared by infiltrating molten Si into gelcasted pure porous carbon preforms derived from mesocarbon microbeads (MCMBs). First large size flaw-free carbon preforms with smooth surfaces were produced by gelcasting method. The porosity and pore size of the carbonized preforms can be adjusted by changing the solid loading (MCMBs) ranging from 40 to 65wt%. Subsequently, C/SiC composites were fabricated by liquid silicon infiltration of the porous carbon preforms. The results show that the preforms with solid loading from 40 to 50wt% were completely infiltrated with Si and formed a C/SiC with homogeneous microstructure. While “SiC shell—black carbon core” structures were observed for the C/SiC composites with solid loading above 50wt%, indicating that the Si infiltrating process was stopped in the surface of the preform. Reaction and infiltration mechanism analysis reveals that the siliconization process of porous carbon preform and the microstructures of the C/SiC samples were mainly affected by the reaction activity of carbon materials and pore structures of carbon preforms.