SiC Materials Research Articles

Thermal strain engineering of mechanical properties in Si-based hybrid sheets via molecular dynamics simulations

The mechanical properties of pristine and defective Si-based hybrid sheets are studied using molecular dynamics calculations for a temperature ranging from 100 to 800 K, in conjunction with a variable strain rate. When increasing temperature, the melting phase of the hybrids occurs from the solid to the liquid phase, while the increase in the strain rate enhances their elastic parameters. The absence of plastic stage reveals that the fracture pattern is brittle in these 2D materials. Under the uniaxial loading, the systems stretch, resulting in the failure of the crystalline skeletons that lose their rigidity with anisotropic behavior observed only for SiC. In defective hybrids, the point defects reduce the values of fracture strength and strain without affecting the brittle behavior of the sheets. The results impart that coupling high temperature to SiC material offers new possibilities for MEMS devices, whereas SiGe is a promising candidate for microelectronic devices.

A modified TCAD simulation model for a-InGaZnO based ISFETs on GaAs substrate for pH sensing applications

In this paper, an ISFET model is established and its accuracy is verified. The model can overcome the limitation of TCAD of not supporting electrolyte solution simulation. The source and drain of the model structure are doped with different types of impurities. The influence of GaAs as a substrate on the device sensitivity is also studied. Amorphous indium gallium zinc oxide (a-IGZO) material is used as a semiconductor layer to obtain a new type of ISFET with a higher detection sensitivity to the pH value. Furthermore, the addition of SiC material to the new ISFET further improves the device sensitivity. The influence of different oxide layers on the model when GaAs is used as a substrate is also studied. The results show that the new ISFET can not only break through the Nernst limit of the device sensitivity (59 mV pH−1), but also increase the sensitivity by nearly 12 times.

Improvement of high‐temperature stability of PIP SiCf/SiC material through in situ grown BNNTs

AbstractIn this paper, the effect of in situ grown boron nitride nanotubes (BNNTs) and preparation temperature on mechanical behavior of PIP (Precursor Infiltration and Pyrolysis) SiCf/SiC minicomposites under monotonic and compliance tensile is investigated. In situ BNNTs are grown on the surface of SiC fibers using ball milling–annealing process. Composite elastic modulus, tensile strength, fracture strain, tangent modulus, and loading/unloading inverse tangent modulus (ITM) are obtained and adopted to characterize the mechanical properties of the composites. Microstructures of in situ grown BNNTs and tensile fracture surfaces are observed under scanning electronic microscopic (SEM). For SiCf/SiC minicomposites with BNNTs, the elastic modulus, tensile strength, and fracture strain are all lower than those of SiCf/SiC minicomposites without BNNTs, mainly due to high preparation temperature and the oxidation of the PyC interphase during the annealing process. Tensile stress–strain curves of SiCf/SiC minicomposites with and without BNNTs are predicted using the developed micromechanical constitutive model. The predicted results agreed with experimental data. This work will provide guidance for predicting the service life of SiCf/SiC composite materials and may enable these materials to become a backbone for thermal structure systems in aerospace applications.

Investigations on the effect of electrical discharge machining process parameters on the machining behavior of aluminium matrix composites

Extensive applications are found in aluminum matrix composites, where high strength to weight ratio, low weight and high corrosion resistance are needed. One of the categories of such materials is the SiC reinforced aluminum matrix composite. This reinforcing material belongs to ceramic group of materials and can withstand high temperature and improve several properties when incorporating in the grain structure of the base matrix. The introduction of SiC enhances wear resistance, hardness value and tensile strength. However, the use of high percentage of SiC material reduces the machinability (ductility) and toughness resistance and the machining of such material becomes difficult. In this current study, an attempt is made to develop an aluminum (LM25 alloy) matrix composite, which is reinforced with 7%SiC and 3%Gr particulates through stir casting route. The fabrication of composite is followed by evaluating the machining behavior of hybrid composite through electric discharge machining. During machining, current, voltage, pulse on time and pulse off time are selected as input controllable variables while material removal rate (MRR), tool wear rate (TWR) and over cut are chosen as responses. The experiments are carried out as per Taguchi's L9 OA, with the aid of ANOVA and significant parameters effecting responses are identified. Main effects plots are drawn and optimum set of input machining conditions are determined.

Manufacture and thermomechanical characterization of wet filament wound C/C‐SiC composites

AbstractThe paper presents manufacture of C/C‐SiC composite materials by wet filament winding of C fibers with a water‐based phenolic resin with subsequent curing via autoclave as well as pyrolysis and liquid silicon infiltration (LSI). Almost dense C/C‐SiC composite materials with different winding angles ranging from ±15° to ±75° could be obtained with porosities lower than 3% and densities in the range of 2 g/cm3. Thermomechanical characterization via tensile testing at room temperature and at 1300°C revealed higher tensile strength at elevated temperature than at room temperature. Thus, C/C‐SiC material obtained by wet filament winding and LSI‐processing has excellent high‐temperature strength for high‐temperature applications. Crack patterns during pyrolysis, microstructure after siliconization, and tensile strength strongly depend on the fiber/matrix interface strength and winding angle. Moreover, calculation tools for composites, such as classical laminate and inverse laminate theory, can be applied for structural evaluation and prediction of mechanical performance of C/C‐SiC structures.

Controllable material removal behavior of 6H-SiC wafer in nanoscale polishing

Controlling material removal uniformity in nanoscale is of importance for the nano-manufacturing process. The interaction between diamond abrasives and 6H-SiC wafer surface during ultra-precision polishing had been analyzed in this study by employing the relevant experiments and molecular dynamics (MD) simulations. The material removal behavior of 6H-SiC wafer through the semi-fixed abrasive polishing pad was obviously controllable. Both the brittle removal and plastic removal were existed during the processing when the cutting depth was uniform with a size of tens of nanometers, while that was the brittle removal when the cutting depth was uneven in this case. The abrasive cutting depth with approximately 4 nm was proved as the critical value of plastic-brittle transition of SiC material. A smooth, scratch-free and nearly damage-free wafer surface could be achieved by controlling material removal uniformly and restricting the abrasive cutting depth in the level of tens of nanometers or less.

Behavior of Silicon Carbide Materials under Dry to Hydrothermal Conditions.

Silicon carbide materials are excellent candidates for high-performance applications due to their outstanding thermomechanical properties and their strong corrosion resistance. SiC materials can be processed in various forms, from nanomaterials to continuous fibers. Common applications of SiC materials include the aerospace and nuclear fields, where the material is used in severely oxidative environments. Therefore, it is important to understand the kinetics of SiC oxidation and the parameters influencing them. The first part of this review focuses on the oxidation of SiC in dry air according to the Deal and Grove model showing that the oxidation behavior of SiC depends on the temperature and the time of oxidation. The oxidation rate can also be accelerated with the presence of H2O in the system due to its diffusion through the oxide scales. Therefore, wet oxidation is studied in the second part. The third part details the effect of hydrothermal media on the SiC materials that has been explained by different models, namely Yoshimura (1986), Hirayama (1989) and Allongue (1992). The last part of this review focuses on the hydrothermal corrosion of SiC materials from an application point of view and determine whether it is beneficial (manufacturing of materials) or detrimental (use of SiC in latest nuclear reactors).

Beneficial effect of low BN additive on densification and mechanical properties of hot-pressed ZrB2–SiC composites

The incorporation of 1 wt% hexagonal BN (hBN) into ZrB2–30 vol% SiC could noticeably better the fracture toughness, hardness, and consolidation behavior of this composite. This research intended to scrutinize the effects of various amounts of hBN (0–5 wt%) on different characteristics of ZrB2–SiC materials. The hot-pressing method under 10 MPa at 1900 °C for 120 min was employed to sinter all designed specimens. Afterward, the as-sintered samples were characterized using X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), and Vickers technique. The hBN addition up to 1 wt% improved relative density, leading to a near fully dense sample; however, the incorporation of 5 wt% of such an additive led to a composite containing more than 5% remaining porosity. The highest Vickers hardness of 23.8 GPa and fracture toughness of 5.7 MPa.m1/2 were secured for the sample introduced by only 1 wt% hBN. Ultimately, breaking large SiC grains, crack bridging, crack deflection, crack branching, and crack arresting were introduced as the chief toughening mechanisms in the ZrB2–SiC–hBN system.

Influence of heating to high temperatures on mechanical properties of boride-based refractory materials

The object of research is HfB2, ZrB2 and ceramics composition HfB2-30 % SiC and ZrB2-20 % SiC, ZrB2-20 % SiC-4 % Si3N4 obtained under high pressure, their mechanical characteristics before and after heating to high temperatures and temperatures of beginning of melting. The research was conducted in order to create new effective refractory materials for use in the aerospace industry. Therefore, the melting temperatures of sintered materials and the effect of heating on their mechanical properties were also studied. Additives (ZrB2-20 % SiC and HfB2-30 % SiC) although led to a decrease in specific gravity. But increased hardness (by 17 % and 46 % in the case of ZrB2 and HfB2, respectively) and fracture toughness (by 40 % and 21 % in the case of ZrB2 and HfB2, respectively). However, significantly reduced the onset of melting temperature in vacuum to 2150–2160 °C. Materials sintered from ZrB2 and HfB2 was not melted after heating to 2970 °C. After heating to a melting point of 2150–2160 °C (in the case of materials with additives) and to temperatures of 2970 °C (in the case of materials sintered with ZrB2 or HfB2), the hardness and fracture toughness decreased. Thus, the hardness of the material prepared from ZrB2 decreased by 19 % and its fracture toughness – by 18 %, and of that prepared from ZrB2–20 % SiC – by 46 % and 32 %, respectively. The hardness of the material prepared from HfB2 decreased by 46 %, its fracture toughness – by 55 %, and of that prepared from HfB2-30 % SiC, after heating decreased by 40 %, but its fracture toughness increased by 15 %. The sintered HfB2 (with a density of 10.4 g/cm3) before heating showed a hardness of HV(9.8 N)=21.27±0.84 GPa, HV(49 N)=19.29±1.34 and HV(98 N)=19.17±0.5, and fracture toughness K1C(9.8 N)=0.47 MH·m0.5, and ZrB2 with a density of 6.2 g/cm3 was characterized by HV(9.8 N)=17.66±0.60 GPa, HV(49 N)=15.25±1.22 GPa and HV(98 N)=15.32±0.36 GPa, K1C(9.8 N)=4.3 MH·m0.5. Material sintered with HfB2-30 % SiC (density 6.21 g/cm3) had Hv(9.8 N)=38.1±1.4 GPa, HV(49 N)=27.7±2.8 GPa, and K1C(9.8 N)=8.1 MH·m0.5, K1C(49 H)=6.8 MH·m0.5. The sintered with ZrB2-20 % SiC material had density of 5.04 g/cm3, HV(9.8 N)=24.2±1.9 GPa, HV(49 N)=16.7±2.8 GPa, K1C(49 H)=7.1 MH·m0.5. The SiC addition to the initial mixture significantly reduces the elasticity of the materials.

Convolutional neural network-based image denoising for synchronous measurement of temperature and deformation at elevated temperature

Non-contact measurement method at elevated temperatures has been widely studied, which provides an efficient means for evaluating the properties of high-temperature materials. However, such high-temperature environment-induced challenges as strong light radiation and air disturbance may cause a huge quality decrease to the captured images based on the optical systems. As an important application of neural networks, Denoising Convolutional Neural Networks (DNCNN) has shown a considerable performance in conventional image denoising. In this work, an optimized DNCNN method based on the sub-region processing and transfer learning was proposed and applied in the high-temperature measurement. The thermal heating experiment of the SiC material was carried out to validate the applicability and accuracy of the method, while the synchronous measurement of temperature and deformation is realized. Simulation results based on the finite element method (FEM) agree well with the calculated data, indicating the proposed model can improve the measurement accuracy.

Oxidation of reaction-bonded silicon carbide-boron carbide in air

The oxidation behaviour of reaction-bonded silicon carbide-boron carbide (RBSBC) in air for durations of 5–96 was investigated in the temperature range of 1250–1350 °C. Scanning electron microscopy observations showed that the oxide layer became uniform after 48 h, with a thickness of 3–5 μm. Transmission electron microscopy, Raman spectroscopy, and secondary ion mass spectroscopy analyses showed that the addition of 7 wt% B4C and a (SiC + Si)/B4C ratio of ∼13 resulted in an amorphous silica-rich borosilicate layer with no phase segregation and random mixing of the borates in the silica network. The oxidation kinetics profile was parabolic, where the transport of ionic oxygen is the rate-controlling step for oxide growth. The oxidation kinetics and activation energy of 353 kJ mol‒1 are close to those reported for CVD-SiC and siliconised-SiC, suggesting that the oxide behaves like pure silica. RBSBC with 7% B4C can provide a more economical alternative to SiC materials for oxidation-resistant applications, with a lower density.

Amorphization resistance of nanocrystalline 3C-SiC implanted with H2+ ions

Compared to single-crystal SiC, nanocrystalline SiC with high densities of stacking faults has been reported to be much more resistant to amorphization under self-ion and electron irradiations. This study examines H2+ ion irradiation-induced amorphization in nanocrystalline 3C-SiC with dense stacking faults using transmission electron microscopy. The results show that full amorphization at room temperature occurs at a comparable dose to that for its single-crystal SiC counterpart under the identical irradiation conditions. Both materials are amorphized as a result of local damage accumulation. The formation of the nucleation sites for amorphization is not appreciably affected by the presence of stacking faults and grain boundaries. The behavior may be attributed to the significant chemical effects of the implanted H atoms that may completely immobilize the point defects in SiC at room temperature. The results suggest cautions be excised to use nanocrystalline SiC materials in high H irradiation environment at room temperature. Further studies of the H behavior at elevated temperatures are warranted.

Influence of SiC hetero-polytype barriers on the performance of IMPATT terahertz diodes

The SiC hetero-polytypes with perfect interfaces and no diffusion pollution are adopted to innovatively design the impact ionization avalanche transit-time (IMPATT) diodes. The performance of DC, large-signal and noise of the proposed diodes operating at the atmospheric low-loss window frequency 0.85 THz are estimated via numerically solving the fundamental device equations with and without quantum correction incorporated the tunnel and density-gradient of carriers. The influence from SiC hetero-polytype barriers and material properties on the performance of IMPATT diodes is analyzed. The advantages in power, efficiency and noise generating in the diodes of 4H/6H–SiC hetero-polytypes can be due to high critical breakdown electric field strength and weak ionizing in 4H–SiC and 6H–SiC. However, small power and heavy noise emerging from the devices of 3C/4H–SiC and 3C/6H–SiC hetero-polytypes can be owing to low critical breakdown electric field strength and strong ionizing in 3C–SiC. The noise electric field peaks arising from the strong ionizing layers while deviating from the interfaces in hetero-polytypes are illustrated. The evident quantum effect on the diodes without 3C–SiC while the slight effect on the devices included 3C–SiC are attributed to low-barriers embedded in the former diodes while high-barriers involved in the latter devices, respectively. • The SiC hetero-polytypes are employed to design the impact ionization avalanche transit-time diodes (IMPATTDs). • The 4H/6H-SiC hetero-polytype IMPATTDs imply advantages in power, efficiency and noise due to weak ionizing in materials. • The noise electric field peaks arise from the strong ionizing layers while deviate from the in hetero-interfaces. • The IMPATTDs with 3C/4H-SiC and 3C/6H-SiC hetero-polytype high-barriers encounter weak quantum effect.

Studies on processing of layered oxide‐bonded porous sic ceramic filter materials

AbstractOxide‐bonded porous SiC ceramic filter supports were prepared using SiC powder (d50 = 212 µm), Al2O3, and clay as bond forming additives and graphite as pore former following reaction bonding of powder compacts at 1400°C in air. Reaction bonding characteristics, phase composition, porosity, pore size, mechanical strength, and microstructure of porous SiC ceramic supports were investigated. Mullite bond phase formation kinetics was studied following the Johnson–Mehl–Avrami–Kolmogorov (JMAK) model using non‐isothermal differential thermal analysis (DTA) data. Compared to porous SiC ceramic filter supports having no needle‐like mullite bond phase, materials processed by the mullite bonding technique exhibited higher average strength (22.1%) and elastic modulus (5.4%) at a similar porosity level of ~38%, with upper and lower bounds of their strength, modulus, and porosity being 39.1 MPa, 40.2 GPa, and 36.3% and 34.2 MPa, 31.3 GPa, and 33.0%, respectively. Spray coating method was applied for preparation of oxidation‐bonded SiC filtration layer having thickness of ~150 µm and pore size of ~5–20 µm over the porous SiC support compacts using aqueous slurry made of fine SiC powder (d50 = 15 µm) followed by sintering. The layered ceramics thus prepared are potential materials for gas filter applications.

New Chemical Technologies Based on Turing Reaction–Diffusion Processes

Diamond–SiC composite materials were obtained by impregnation with gaseous and liquid Si. The mechanisms of the impregnation and consolidation of the diamond–silicon carbide composites were studied. The effect of the Turing reaction–diffusion mechanism on the sintering of the diamond–SiC materials, the formation of the microstructure, and the mechanical properties was shown for the first time.

Improving Thermal Effects and Reduction of Self-heating Phenomenon in AlGaN/GaN/Si Based HEMT

In this paper, we reduce the self-heating effects of high-electron-mobility transistors (HEMT) by using changes in material and structure. In the first step, the 6H-SiC layer is used both as a substrate layer and as a passive layer. The thermal conductivity of SiC materials is very high, which reduces the heat under the gate. In the second step, the barrier layer is used by a combination of AlGaN and InGaN as a heterojunction. InGaN material is used at the point where the hot spot occurs. These changes in the barrier layer cause the heat to be uniformly distributed under the gate, so that the combination and recombination of electrons and holes in the hot spot are reduced. In the next step, the heat generated in the structure is directed to outside of the structure by a metal plate or field plate. In this paper, the selected structure for reference is fabricated in recent years. Different layers of materials have been grown on the Si substrate layer (AlGaN/GaN/Si). After the changes, the output current increased by 25%, and overall the heat generated in the structure decreased by 40%. The proposed structure is suitable for high-power and high-frequency circuits.

Exploring n‐type SiC film with ultralow work function Cs coating surface for solar cell anode

In this study, the Cs adsorption behavior on n-type 3C-SiC (0001)-(2 × 1) and -(3 × 2) reconstructed surfaces are investigated via first-principles calculations. The potentiality of 3C-SiC as the anode material of solar cell based on photon-enhanced thermionic emission (PETE) is discussed. Various doping configurations are considered for the determination of an optimum n-type doping structure. Cs-covered (3 × 2) surface exhibits stronger stability compared with (2 × 1) surface. The charge transfer caused by Cs adsorption produces a [Cs+-SiC] dipole moment directing from Cs adatom to reconstructed surface, resulting in an effective declination of work function. Specifically, 0.5 ML Cs coverage surface provides an ultralow work function with 0.9 eV, demonstrating its potential application in PETE devices. Combining with a photoemission model, the maximum conversion efficiency can attain 30% utilizing SiC as an anode. Moreover, the Mulliken charge analysis provides the details of surface charge transfer and implies the inner mechanism of work function alteration. This study provides guiding significance for the synthesis of SiC material with low work function and an effective theoretical method for the design of high-performance anode materials in application of PETE devices. The adsorption mechanism of Cs on n-type doped 3C-SiC(0001)-(2 × 1) and -(3 × 2) reconstructed surfaces and its application as the anode material of solar cell are systematically investigated. For one Cs adatom adsorption, Cs-covered (3 × 2) surfaces present stronger stability compared with (2 × 1) surfaces. Cs-decorated (3 × 2) surface with 0.5 ML coverage exhibits an ultralow work function as low as 0.9 eV. Based on the photoemission model, the maximum conversion efficiency of PETE devices with SiC anode can reach 30%. Highlights Cs-decorated SiC surfaces with ultralow work function are suitable as PETE anode materials. Cs adsorption mechanism on 3C-SiC(0001)-(2 × 1) and -(3 × 2) surfaces are explored. The optimum n-type doped (2 × 1) and (3 × 2) surfaces are, respectively, determined. 0.5 ML Cs-adsorbed (3 × 2) surfaces show an ultralow work function of 0.9 eV. Cs adsorption induces a [Cs+-SiC] dipole moment on (2 × 1) and (3 × 2) surfaces.

Tribological behavior of friction stir processed AA6061 aluminium alloy

Abstract In the age of light weight, aluminum alloys are used as one of the most predominant materials in automotive and aircraft industries. But their applications are being restricted where tribological (relative motion between parts) is major issue. Thus, coating metallic substrates i.e. aluminum alloys with ceramic powders is an effective solution in prolonging the component service life. The present investigation aims at changing the surface morphology by introducing carbide powders (180 µm) of boron, silicon and tungsten on to AA 6061 Al alloy (widely used in automobile components) using friction stir processing. Fabricated surface metal matrix composites (SMMCs) exhibited better wear resistance compared to the base metal. SMMC (127VHN) consisting B4C as reinforcement has shown superior wear resistance among other SMMCs made from WC and SiC respectively. From the SEM analysis, it is clearly observed that abrasion wear is the primary cause for less wear resistance in AA 6061 aluminium alloy while as adhesive wear mechanism is found to be predominant one in all other surface composites resulting in the increase of wear resistance. Thus, it is recommended to use B4C as reinforcing material for surface modification of AA6061 aluminum alloy when compared with other reinforcing materials of WC and SiC.

Effect of arc current on SiC fabrication from rice husk ash and diatomite in electric arc discharge furnace

AbstractSilicon carbide (SiC) was synthesized from Vietnamese rice husk ash and diatomite via the Acheson process in a graphite electric arc furnace. In this type of furnace, arc current generates temperature and therefore effect on the formation of SiC. The influence of arc current at 100, 150 and 200 A was investigated. Scanning electron microscopy and energy dispersive spectroscopy, XRD and Raman spectroscopy were performed to analyze the formation of SiC materials. Results showed the weight percentage of SiC in the synthesized product increased as the arc current increased.

Hollow SiC microtube with multiple attenuation mechanisms for broadband electromagnetic wave absorption

The hollow SiC microtubes were designed and prepared by the de-template of SiC/CF coaxial materials to enhance the electromagnetic wave absorption bandwidth of the SiC materials. The XRD, Raman, and TEM results indicated that the hollow SiC microtubes were composed of SiC, C, and amorphous SiO2 layers. The carbon particles uniformly embedded in the SiC particles and the amorphous SiO2 covered the outside of the SiC microtube. The dielectric properties of the hollow SiC microtube could be optimized by controlling its wall thickness. The hollow SiC microtube showed a broader electromagnetic wave absorption bandwidth compared to that of other SiC materials. The minimum reflection loss of hollow SiC microtube was −25.7 dB@14.9 GHz, and the effective absorption bandwidth was 5 GHz covering from 12.9 GHz to 17.9 GHz at a sample thickness of 2 mm. The uniform distribution of carbon contributed to improving the conduction loss of hollow SiC microtube. The interfacial relaxation loss causing by the outermost SiO2 layer enhanced the dielectric loss of the tubular SiC. Besides, the unique hollow structure of the SiC microtube significantly promoted the multi reflection and scattering of electromagnetic waves. The multiple attenuation mechanisms of tubular SiC highlighted the design of a novel structure for a high-performance electromagnetic wave absorber.