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Silicon carbide (SiC) ceramic is being increasingly applied in several engineering fields owing to its excellent saturation electron drift rate. Although much attention is paid to its material removal mechanism, producing a high‐quality SiC surface with a high material removal rate is still a challenging issue. Therefore, there is a need to investigate the material removal mechanism of SiC to improve the processing performance. In this study, the laser heating‐assisted nanocutting models are established using a molecular dynamics method. Then, a laser beam with various energies is irradiated onto the SiC. The influence of average laser power on the nanocutting mechanism of SiC is revealed in terms of the temperature of the machined region, cutting force, stress distribution state, subsurface damage, and tool wear. The results demonstrate that within the scope of this study, the using of laser irradiation methods has a positive effect on the machinability of SiC at the nanoscale, provided that the laser power density does not exceed the ablation threshold. Meanwhile, the results indicate that laser heating‐assisted methods have played an important role in suppressing tool wear. This study has significant theoretical and practical value in processing technology. [ABSTRACT FROM AUTHOR]

The tribological properties of carbon–carbon antifriction composite materials reinforced with carbon fabric based on polyacrylonitrile and viscose raw materials have been studied. Tribological tests were carried out according to the ring–disc scheme paired with silicon carbide ceramics under dry friction conditions with different orientations of the composite fabric layers relative to the friction surface in the temperature range of 80–100°C. Dependences of the friction coefficient and wear rate on the fabric orientation relative to friction surface, structure of the composite, and properties of its structural components were obtained at a fixed load and sliding speed. The surface of composites was analyzed after tribological tests using scanning electron microscopy and optical profilometry. The composites friction and wear mechanisms for different contact configurations and different material properties have been revealed. The characteristic features of composite individual structural (fibers, fiber bundles, layers of reinforcing fabric) frictional destruction have been determined. It has been established that the film of wear products formed on the friction surface has a decisive influence on the tribological characteristics of the studied materials. Combinations of the fabric base of the composite, its orientation relative to the friction surface, and the heat treatment mode of the material were determined, which simultaneously provide increased wear resistance and reduced friction in tandem with a ceramic counterbody. [ABSTRACT FROM AUTHOR]

SiC ceramics has been extensively used in heat exchangers because of their excellent mechanical properties, high thermal conductivity, and superior thermal shock, corrosion, and oxidation resistance. However, there is a wide variation in the thermal conductivity of SiC ceramics, depending on the raw materials, molding process, sintering process, and sintering additives. The thermal conductivity of SiC ceramics (≤ 270 W·m-1·K-1) is much lower than that of 6H-SiC single crystals (490 W·m-1·K-1) because of pores, grain boundaries, impurities, and defects in SiC ceramics. In this work, the important factors affecting the thermal conductivity of SiC ceramics were analyzed, including temperature, pore, crystal structure, and second phase. Further, the preparation processes of high conductivity SiC ceramics were systematically compared based on hot-pressed sintering, spark plasma sintering, pressureless sintering, recrystallization sintering, and reaction sintering. The improvement measures of thermal conductivity of SiC ceramics were summarized, including the optimization of the type and content of sintering aids, high-temperature annealing, and adding a high-thermal-conductivity second phase. Finally, the prospects and research directions of low-cost and high-thermal-conductivity SiC ceramics are proposed.

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Silicon carbide ceramics are widely used in many industrial fields owing to their outstanding physical and chemical characteristics. However, their inherent hardness and brittleness make the grinding process very difficult compared to that involving ductile materials. In the present study, the effects of the biomimetic fractal-branched structure, inspired from the leaf-vein, on the grinding behavior of silicon carbide were investigated. Two biomimetic fractal-branched structures with different densities of micro-channels were designed and compared with the non-structured silicon carbide surface. The surface of the silicon carbide ceramic was textured through pulsed-laser ablation. Thereafter, the grinding experiment was conducted on the biomimetic fractal-branched and non-structured workpieces. The surface topography, subsurface damage, grinding force, grinding force ratio, surface roughness and grinding wheel wear were examined throughout the experiment. The experimental results indicated that the normal and tangential grinding forces for the fractal-branched structure surface are 7.61–18.21% and 8.34–26.13% lower than those for the non-structured surface. The grinding force ratio also increased significantly with an increase in the micro-channel density. In addition, a larger volume of coolant was transported through the grinding zone of the fractal-branched structure. The research results confirmed that the biomimetic fractal-branched structure on the silicon carbide surface enhanced the grinding performance and improved the grinding quality. [ABSTRACT FROM AUTHOR]

Over the years, stereolithography has been successfully used to prepare complex, strong silicon carbide (SiC) structures. However, most raw materials are dark in color and therefore have broad-spectrum absorbing properties, making the curing steps during stereolithography highly inefficient. Here, diamond powders were mixed with a light-curing resin, yielding a slurry with excellent curability. The slurry was then used to prepare SiC-based composites with complex morphologies using pyrolysis and reaction melt infiltration (RMI) process. The influence of the diamond volume fraction in the slurry on each process stage was investigated. The infiltration of molten Si into diamond body during RMI was greatly enhanced compared to traditional carbon bodies. SiC ceramic-based composites with complex morphologies and a maximum strength of ∼460 MPa was prepared rapidly and efficiently. This study demonstrates the great potential of the slurry for efficiently manufacturing SiC-based composites in mechanical parts where high strength and complex structures are needed. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) ceramics prepared by the conventional process has excellent properties and wide application prospects, but the increased cost of high-temperature preparation process restricts its further development. In contrast, the abundant porous structure of biomass makes itself to be ideal replacement of SiC ceramic prepared at low temperature. This paper reviewed the structure characteristics, preparation methods, pyrolysis mechanism and influence parameters of biomass-based SiC ceramic, and eventually explored the current problems and development trends of the pretreatment of carbon source and silicon source, the pyrolysis process and the application research on the preparation for biomass-based SiC ceramic.

The current investigation presents detailed finite‐element simulations of coating stress analysis for a three‐dimensional, three‐layered model of a test sample representing a typical gas turbine component. Structural steel, titanium alloy, and silicon carbide are selected for main inner, middle, and outermost layers respectively. ANSYS is used to conduct three types of analysis—static structural, thermal stress analysis, and also computational fluid dynamic erosion (via ANSYS FLUENT). The specified geometry, which corresponds to corrosion test samples exactly, is discretized using a body‐sizing meshing approach, comprising mainly of tetrahedron cells. Refinements were concentrated at the connection points between the layers to shift the focus toward the static effects dissipated between them. A detailed grid independence study is conducted to confirm the accuracy of the selected mesh densities. The momentum and energy equations were solved, and the viscous heating option was applied to represent the improved thermal physics of heat transfer between the layers of the structures. A discrete phase model (DPM) in ANSYS FLUENT was used, which allows for the injection of continuous uniform air particles onto the model, thereby enabling an option for calculating the corrosion factor caused by hot air injection. Extensive visualization of results is provided. The simulations show that ceramic (silicon carbide) when combined with titanium clearly provide good thermal protection; however, the ceramic coating is susceptible to cracking and the titanium coating layer on its own achieves significant thermal resistance. Higher strains are computed for the two‐layer model than the single layer model (thermal case). However even with titanium only present as a coating the maximum equivalent elastic strain is still dangerously close to the lower edge. Only with the three‐layer combined ceramic and titanium coating model is the maximum equivalent strain pushed deeper towards the core central area. Here the desired effect of restricting high stresses to the strongest region of the gas turbine blade model is achieved, whereas in the other two models, lower strains are produced in the core central zones. Generally, the CFD analysis reveals that maximum erosion rates are confined to a local zone on the upper face of the three‐layer system which is in fact the sacrificial layer (ceramic coating). The titanium is not debonded or damaged which is essential for creating a buffer to the actual blade surface and mitigating penetrative corrosive effects. The present analysis may further be generalized to consider three‐dimensional blade geometries and corrosive chemical reaction effects encountered in gas turbine aero‐engines. [ABSTRACT FROM AUTHOR]

• The SiC surface is oxidized and reduces the polishing force. • A photocatalytic roller vibration composite polishing device was built. • The agglomeration are alleviated and the polishing uniformity is improved. Due to serious damage problems, low efficiency, and poor quality of silicon carbide ceramic (SiC) polishing, a UV based photocatalytic-roll-vibrated composite polishing method is proposed in this paper. The proposed method can conveniently, accurately, and efficiently planarize SiC. The removal mechanism of the SiC photocatalytic-roll-vibrated composite polishing method is also discussed. The effects of photocatalysis and vibration on the degradation time of methyl orange are revealed based on methyl orange degradation experiments. The SiC surface indentation experiment is carried out to compare the mechanical properties of the SiC surface before and after the photocatalytic reaction. Thus, the influence of photocatalysis and vibration on the mechanical properties of the material is revealed, while the oxidation law and processing effectiveness of photocatalytic-roll-vibrated composite polishing are clarified. Moreover, the photocatalytic-roll-vibrated composite polishing comparison experiment is carried out, and the influence of photocatalysis and vibration on the polishing effect is analysed. The effects of photocatalytic parameters (ultraviolet intensity) and vibration parameters (frequency and amplitude) on surface roughness, surface peak-to-valley value and material removal rate are revealed. The results indicate that the photocatalytic-roll-vibrated composite polishing method can be used for polishing silicon carbide ceramics (SiC) under the irradiation of ultraviolet light of 365 nm, which improves the polishing effect. [ABSTRACT FROM AUTHOR]

The main goal of this numerical and experimental study of composite armour systems was to investigate their ballistic behaviour. Numerical simulations were employed to determine the initial dimensions of panel layers before the actual ballistic test. In order to achieve this aim, multivariate computations with different thicknesses of panel layers were conducted. Numerical calculations were performed with the finite element method in the LS-DYNA software, which is a commonly used tool for solving problems associated with shock wave propagation, blasts and impacts. An axisymmetric model was built in order to ensure sufficient discretization. Results of a simulation study allowed thicknesses of layers ensuring assumed level of protection to be determined. According to the simulation results two armour configurations with different ceramics have been fabricated. The composite armour systems consisted of the front layer made of Al2O3 or SiC ceramic and high strength steel as the backing material. The ballistic performance of the proposed protective structures were tested with the use of 7.62 mm Armour Piercing (AP) projectile. A comparison of impact resistance of two defence systems with different ceramic has been carried out. Application of silicon carbide ceramic improved ballistic performance, as evidenced by smaller deformations of the second layer. In addition, one of armour systems was complemented with an intermediate ceramic-elastomer layer. A ceramic-elastomer component was obtained using pressure infiltration of gradient porous ceramic by elastomer. Upon ballistic impact, the ceramic body dissipated kinetic energy of the projectile. The residual energy was absorbed by the intermediate composite layer. It was found, that application of composite plates as a support of a ceramic body provided a decrease of the bullet penetration depth. [ABSTRACT FROM AUTHOR]

A novel hybrid process that integrates end electric discharge (ED) milling and mechanical grinding is proposed. The process is able to effectively machine a large surface area on SiC ceramic with good surface quality and fine working environmental practice. The polarity, pulse on-time, and peak current are varied to explore their effects on the surface integrity, such as surface morphology, surface roughness, micro-cracks, and composition on the machined surface. The results show that positive tool polarity, short pulse on-time, and low peak current cause a fine surface finish. During the hybrid machining of SiC ceramic, the material is mainly removed by end ED milling at rough machining mode, whereas it is mainly removed by mechanical grinding at finish machining mode. Moreover, the material from the tool can transfer to the workpiece, and a combination reaction takes place during machining. [ABSTRACT FROM AUTHOR]

Abstract: Thermochemical hydrogen production process is one of the candidates of industrial fossil fuel free hydrogen production. Japan Atomic Energy Agency (JAEA) has been conducting R&D of the thermochemical water splitting iodine-sulfur (IS) process since the end of 1980s. This paper presents the recent study on the IS process in JAEA. In 2005-2009, test-fabrication of components, collection of design database, improvement of process components for higher thermal efficiency, and proposition of composition measurement method were carried out. On the basis of them, the integrity test of process components is carried out in 2010-2014 to examine their integrities in severe process environments. At present, a Bunsen reactor, which produces acids, and incidental equipments has been already manufactured using corrosion resistant materials such as glass lining steel and fluoroplastic lining steel. Flow tests to examine the functionality and integrity of the materials are planned in 2012. [Copyright &y& Elsevier]

The paper presents a feasibility study on application of the gas tungsten arc welding (GTAW) process to obtain metal composite functional coating for advanced tribological application. Silicon carbide (SiC) particles in the form of powder was added to a weld pool in autogenous mode as well as with an additional filler wire. Powder feeding was carried out at different angles and with varying separation distance from the welding torch. The metallurgical characterization of the cladded structure was carried out using optical as well as scanning electron microscopy (SEM). Energy dispersive X-ray spectroscopy (EDS) was performed to analyze the composition of the deposited weld metal. It has been observed that due to low SiC density it was difficult for particles to penetrate the weld pool. Also the added SiC was found to be dissociated into Si and carbon (C) and the large amount of dissolved C in the weld pool resulted in formation of graphite phases. [ABSTRACT FROM AUTHOR]

Abstract: Porous silicon carbide ceramics were prepared through the coat-mix method and molding, carbonization and sintering process with silicon powders and phenolic resin as raw materials. The crystalline phase, microstructure, and porosity of samples treated at different stages were characterized. Results showed that the fabricated porous silicon carbide ceramics consist of pure β-SiC phase with a homogeneous structure and porosity of above 60%. Each of the processing stages, including coat-mix, molding, carbonization, and sintering, has certain contribution to the porosity of the final porous silicon carbide ceramics, in which the mole ratio of resin carbon to silicon and the molding temperature are the main factors to affect the porosity. A porosity evolution process of porous silicon carbide ceramics during fabrication process was also proposed. [Copyright &y& Elsevier]

Silicon carbide (SiC) ceramic has been widely used in modern industry because of its superior mechanical properties, wear, and corrosion resistance even at elevated temperature. However, the manufacture of SiC ceramic is not an efficient process by conventional machining methods. This paper employs a steel-toothed wheel as the tool electrode to machine SiC ceramic using electric discharge milling. The process is able to effectively machine a large surface area on SiC ceramic. To further improve the process performance, three kinds of emulsion are proposed as the dielectric in this paper. The effects of dielectric, tool polarity, pulse duration, pulse interval, peak voltage, and peak current on the process performance such as the material removal rate (MRR) and surface roughness (SR) have been investigated. Furthermore, the microstructure of the machined surface is examined with a scanning electron microscope (SEM), an energy-dispersive spectrometer (EDS), and X-ray diffraction (XRD). [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) ceramic has been widely used in modern industry for its excellent physical and mechanical properties. However, SiC ceramic is difficult to machine owing to its high hardness and brittleness. This article presents a novel compound process that integrates end electric discharge (ED) milling and mechanical grinding to machine SiC ceramic. The process is able to effectively machine a large surface area on SiC ceramic with a good surface quality. The effect of tool polarity on the machining characteristics such as the material removal rate (MRR), tool wear ratio (TWR), and surface roughness (SR) has been explored. The effects of pulse on-time, pulse off-time, discharge current and open voltage on MRR, TWR, and SR have been investigated with Taguchi experimental design. The experimental data are statistically evaluated by analysis of variance and stepwise regression. The significant machining parameters, the optimal combination levels of machining parameters, and the mathematical models associated with the machining characteristics are obtained. The confirmation experiment results confirm the validity of the used Taguchi method for enhancing the machining performance and optimizing the machining parameters. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) ceramic has been widely used in modern industry. However, the beneficial properties of SiC ceramic make machining difficult and costly by conventional machining methods. This paper proposes a new process of machining SiC ceramic using end electric discharge (ED) milling. The process is able to effectively machine a large surface area on SiC ceramic at low cost and no environmental pollution. The effects of emulsion concentration, emulsion flux, milling depth, copper electrode number, and copper electrode diameter on the process performance such as the material removal rate, electrode wear ratio, and surface roughness have been investigated. In addition, the microstructure of the machined surface is examined with a scanning electron microscope, and the material removal mechanism of SiC ceramic during end ED milling is obtained. [ABSTRACT FROM AUTHOR]

Abstract: A new process of machining silicon carbide (SiC) ceramic using end electrical discharge milling is proposed in this paper. The process is able to effectively machine a large surface area on SiC ceramic with good surface quality and low cost. The effects of machining conditions on the material removal rate, electrode wear ratio, and surface roughness have been investigated. The surface microstructures machined by the new process are examined with a scanning electron microscope (SEM), an energy dispersive spectrometer (EDS), and an X-ray diffraction (XRD). The results show that the SiC ceramic is removed by melting, evaporation and thermal spalling, the material from the tool electrode can transfer to the workpiece, and a combination reaction takes place during end electric discharge milling of the SiC ceramic. [Copyright &y& Elsevier]

A possibility of microstructuring the surface of silicon carbide ceramic by pulse-periodic laser treatment was determined for reducing the coefficient of friction under actual contact stress conditions that occur in elements of the rolling bearing in operation. Temperature rate conditions for the laser treatment with pulse duration in the millisecond range were found, which lead to a change in the surface microrelief of silicon carbide ceramic obtained by diamond grinding after hot isostatic pressing. The determination of the coefficient of sliding friction was conducted with using the ball-on-disk tribometer at normal loads, which corresponds to the values of contact stresses of (0.5–1)×10 9 Pa. When the load was increased to the upper limit of measuring range, the friction coefficient decrease after laser treatment was more than 30% compared to the initial structure. Significant reduction of friction in rolling bearings up to this level provides an opportunity to improve efficiency of various machines. [ABSTRACT FROM AUTHOR]

A new method which employs a group pulse power supply for electric discharge milling of the silicon carbide ceramic with the resistivity of 500 Ω.cm is presented. Due to the good machining stability and high pulse utilization, the material removal rate (MRR) can reach 72.9 mm³/min. The effects of high-frequency pulse duration, high-frequency pulse interval, peak voltage, peak current, polarity, rotate speed and group frequency on the process performance have been investigated. Also the EDMed surface microstructure is examined with a scanning electron microscope (SEM), an X-ray diffraction (XRD), an energy dispersive spectrometer (EDS) and a micro hardness tester. The results show that the conditions of smaller high-frequency pulse duration and pulse interval, higher peak voltage and peak current, and positive tool polarity are suitable for machining the SiC ceramic. The optimal rotate speed is 1090 r/min and the preferable group frequency is 730 Hz. In addition, there is a small quantity of iron on machined surface when machining with steel electrode. The average grain size of the EDMed surface is smaller than that of the unprocessed, and the micro hardness of machined surface is superior to that of the unprocessed. [ABSTRACT FROM AUTHOR]