Reaction-bonded Silicon Carbide Research Articles

Wettability and joining of reaction-bonded silicon carbide (RBSC) by Ti–Si eutectic alloy

The high-strength joining of reaction-bonded silicon carbide (RBSC) is pivotal for its application in the semiconductor field. In this paper, the wetting and joining mechanism of Ti–Si eutectic alloy on RBSC were investigated. The contact angles observed between Ti–Si eutectic alloy and RBSC were approximately 1.9°, indicating the favorable wettability and demonstrating the feasibility of bonding RBSC joints. The temperature bending strength of the joints initially increased and then decreased as the brazing temperature increased. Moreover, the shear strength of approximately 107.38 ± 5.56 MPa was achieved at 1350 °C for 30 min. Notably, the diffusion and amalgamation of atoms, lead to the establishment of stronger bonds between adjacent particles. Thus, the Ti–Si eutectic alloy brazing filler formed a direct connection with the RBSC matrix, with Si2Ti infiltrating into the base metal on both sides. The utilization of Ti–Si eutectic alloy brazing filler in RBSC joints exhibits promising prospects.

Enhancing the grinding performance of RB-SiC ceramic using abrasive water jet dressed diamond grinding wheels

Reaction-bonded silicon carbide (RB-SiC) is regarded as difficult-to-machine ceramic materials with extremely high strength and hardness. The work focuses on the grinding performance evaluation of RB-SiC ground by the dressing diamond grinding wheel with AWJ. Orthogonal experiments studied the influence of processing parameters on grinding force and 3D surface roughness, with the response surface method identifying optimal parameters. Explanation of the ground surface topography and 3D surface roughness in a comprehensive manner shows that an erosion of the bonding material by micro-cutting but diamond grains are being pulled out rather than cut. Results reflect a correlation between surface topography and diamond wheel dressing. The results are of great significance for future formulating an appropriate grinding process to machine RB-SiC ceramics.

1300°C–1900 °C heat treatment and mechanical properties optimization of RB-SiC ceramics

For reaction-bonded silicon carbide (RB-SiC) ceramics, the use temperature cannot exceed 1300 °C due to the existence of free silicon. In order to improve its high temperature performance, RB-SiC ceramics were treated by vacuum heat treatment above 1300 °C to remove free silicon, and then modified by post-impregnation pyrolysis (PIP) process with polycarbosilane (PCS). The porosity, bulk density, and flexural strength of the ceramics were measured system atacially. The results show that the RB-SiC can completely remove the free Si, when the temperature exceeds 1700 °C. But its mechanical strength is significantly reduced. The strength of RB-SiC heat-treated after 1900 °C is generally higher than that of materials heat-treated below 1800 °C. In the PIP process, the pyrolysis products of PCS are evenly distributed in the pores of vacuum-heat-treated ceramics (VHT-SiC) to replace the initial free silicon. After 5 PIP cycles, the bulk density of the VHT-SiC increased from 2.56 g cm−3 to 2.70 g cm−3, the porosity reduced from 17.22 % to 12.04 %, and the flexural strength increased by 35.56 %. Therefore, this work provides a simple and efficient method for the preparation of complex SiC components with high temperature resistance (>1400 °C).

A new method for machining RB-SiC with high efficiency and quality: Laser assisted ultrasonic grinding

Reaction Bonded Silicon carbide (RB-SiC) ceramic is preferred material for space mirrors in aerospace field. However, the high hardness, brittleness and inhomogeneous structure bring great challenges for high quality and efficient machining. In this study, laser ablation assisted ultrasonic grinding (LAAUG) process was proposed. The high efficiency of laser ablation and high quality of ultrasonic grinding were effectively combined. Laser pre-ablation experiments were carried out firstly, and then thermal damage layer was removed through ultrasonic grinding. The results show that RB-SiC ceramics transform into relatively loose and homogeneous ablation products (SiO2 and recrystallized SiC) by laser irradiation. Moreover, it is accompanied by cracks development. Compared with conventional grinding, the maximum reduction of grinding force and surface roughness is 34 % and 13.8 %, respectively. Abrasive grain wear is significantly restrained and the percentage of plasticity removal is improved. This study indicates that LAAUG is feasible and efficient method for machining RB-SiC ceramics.

High-temperature self-healing behavior of reaction-bonded silicon carbide porous ceramic membrane supports

Reaction-bonded silicon carbide porous ceramics (SCPCs) are increasingly employed as membrane supports for the high-temperature filtration. However, the inevitable expansion of cracks limits their application. Herein, we studied the crack propagation behavior of SCPCs and discovered the commendable self-healing properties at high temperatures. Results show that the optimal healing conditions are 1200 °C for 2 h, which can recover the strength from 41.9% to 88.4%, and maintain the initial pore structure and permeance. This is mainly attributed to the infiltration of the multi-phase oxide melt that healed the cracks rather than the oxidation of SiC. Neck cracks are more prone to healing than surface cracks on SiC particles due to the residual compressive stress and a high proportion of melt volume. Nonetheless, the recovery of residual compressive stress and the crack width constrain the upper limit of strength recovery. These insights lay the groundwork for the high-temperature industrial application of SCPCs.

Precision grinding of ceramics and ceramic-matrix composites surfaces with controllable microarray structures

The precision micro-tip truing and micro-grinding technology is proposed to process controllable microarray structures on the surfaces of ceramics and ceramic-matrix composites in this paper. It involves the mechanical truing of a metal-bonded diamond grinding wheel along V-shaped cross interpolation trajectories for creating sharp cutting edges. The trued V-tip grinding wheel was utilized to machine regular microarray structures on the surfaces of single crystal silicon carbide (SiC), silicon carbide reinforced aluminum (Al/SiCp), reaction-bonded silicon carbide (RB-SiC) and glass ceramic. The morphology of the trued grinding wheel, as well as the V-tip profile, arc radius, tip angle, form accuracy, and morphology of the ground microarray structures were analyzed. The results indicate that ground RB-SiC surface exhibits the highest processing quality, while glass ceramic has the lowest. Additionally, the errors of the bottom angle of V-grooves on all four ceramic materials are less than 1°, and form accuracy PV value is controlled within 18 µm. Overall, it is a highly efficient and accurate method for processing microarray structures on ceramics and ceramic-matrix composites.

Tribological behavior of diamond coated reaction-bonded silicon carbide under dry and seawater environment

Ceramic seal materials such as Silicon carbide (SiC) and Reaction-Bonded SiC (89%SiC and 11 % free Silicon) are widely used in mechanical pumps, compressors, and feed water pumps to prevent the fluid leakage between the two rotating shafts. In a continuously harsh environment, these mechanical seal materials undergo high friction and wear due to the high asperity-to-asperity contact between the two mating parts and generate high frictional heat at the interface. This scenario induces seal failure under high operating conditions. Especially in corrosive mediums such as acids, high pH value solutions, and hard abrasive media can cause aggressive seal failure. To reduce production downtime and improve the longevity of the mechanical seal, the surface of the seal material needs to be engineered with a suitable coating that will satisfy the required properties of high hardness, chemically inertness, and low friction coefficient. In this regard, we have come up with a super hard coating material such as diamond (Micro-crystalline) on the surface of Reaction-Bonded SiC using the hot filament CVD (HFCVD) method to meet the above-required properties. In this work, we have carried out a systematic study on the tribological effect of uncoated, and diamond-coated seal material against silicon nitride ceramic under a dry and seawater environment. The initial physical characteristics such as surface morphology, surface roughness, and Raman analysis were performed on the samples before and after coating. To understand the friction and wear characteristics, the linear reciprocating tribometer test (Ball on Flat) was conducted on the uncoated and diamond-coated samples using a universal tribometer for an operating period of 36,000 cycles. The experimental results show that the diamond-coated sample exhibits a low friction coefficient (0.05 ± 0.01) compared to the uncoated sample (Friction coefficient (CoF) = 0.24 ± 0.037) at a normal load of 10 N with a frequency of 10 Hz under a seawater environment. Similarly, under dry conditions for the same tribo-test parameters, the diamond-coated sample (CoF = 0.06 ± 0.02) outperforms compared with the uncoated sample (CoF = 0.42 ± 0.17) at a percentage improvement of 85 %. From the observed results, we conclude that diamond-coated ceramic seals are considered a suitable alternative to commercially available seals in terms of high operating conditions and durability under both wet (seawater) and dry running operations.

Controllable reduction of absorbance and two-step reaction for 3D-printed SiC ceramics with micron-level periodic structure

Digital light processing (DLP) is increasingly widely used to manufacture high-precision complex structural ceramic components quickly and efficiently. However, due to the high absorbance of silicon carbide (SiC) micron fine powder and the high refractive index difference between the powder and the photosensitive resin, it is extremely challenging to DLP print SiC with high precision complex structure. Here, the surface of SiC powder was coated with SiO2 nano-layer of different thickness by controllable oxidation coating method, thus realizing the photocurable printing of SiC@SiO2 green bodies with structural precision up to 80 μm. Through the two-step reaction method of carbothermal reduction combined with gas-phase siliconizing (GSI), not only the SiO2 coated layer was effectively removed, but also the reaction-bonded silicon carbide (RB-SiC) ceramics with 80–300 μm periodic structure was successfully realized. Ultimately, the comprehensive performance of the RB-SiC samples is effectively improved by chemical vapor infiltration of silicon carbide (CVI-SiC). It is noteworthy that the maximum elastic modulus and hardness of the ultima SiC specimens (RB-SiC@CVI-SiC) are as high as 394.599 GPa and 50.241 GPa, respectively. Shockingly, the nanomechanical properties of postgenetic RB-SiC bound to initial α-SiC on the cross-section of ultima specimens were much higher than those of CVI-SiC on the surface. This study fills the gap that liquid-phase siliconizing (LSI) or pyrolysis process could not achieve high-performance SiC ceramics with micron-level periodic structure.

Spray drying as a one-step production method of SiC-based granulates for direct reactive laser sintering of Reaction Bonded Silicon Carbide (RBSiC)

This research is focused on the development and production of SiC-based granulates for reactive laser sintering. Ceramic slurries with different compositions of SiC, Si, C powders, and PVA binder were subjected to spray drying. Carbon source in form of latex was proposed to avoid a reaction of Si with H2O in alkalic pH caused by the presence of carbon in the slurry. It was observed that the latex was beneficial for improvement of the flowability. Selected granulates were subjected to laser processing using two different methods. The first one where SiC-based granulates were spray deposited on a SiC substrate and laser treated with single pulse working of the laser. The second method where a pressed green sample of SiC were processed by the continuous working mode of the laser. Results revealed that the use of the continuous work mode during laser processing allowed to produce Reaction Sintered SiC (RBSiC).

Diffusion behaviour and corrosion rate of rare earth monosilicate-based EBCs under CMAS exposure

The thermochemical corrosion behaviour of different rare earth (RE)-based (Yb, Lu and Er) environmental barrier coatings (EBCs) between 1 and 48 h in low calcium–magnesium–aluminosilicate (CMAS) load environments at 1300 °C was studied. The EBCs were coated on reaction-bonded SiC–B4C substrates using the dip-coating method. Each coating is composed of a dense RE2SiO5-based bottom coat and a porous RE2O3 topcoat. The microstructures and compositions of the corroded samples were examined using scanning electron microscopy and energy dispersive spectroscopy. CMAS infiltrated the topcoat through pores and cracks, settled in these defects, and dissolved in the neighbouring coating areas to precipitate as a Ca–Mg–Si–RE garnet. The diffusion coefficients of Ca and Si in the CMAS–EBC corroded specimens were calculated. Yb and Lu silicates have the lowest diffusion coefficient values, whereas Er silicate has the highest values. The formed garnet filled the pores and inhibited further diffusion of corrosive species in the coat. The corrosion rates were calculated based on the physical properties of the coat and found to be lower than those of coatings produced using atmospheric plasma spraying. The diffusion coefficient and corrosion rate were successfully used to evaluate various corrosion-resistant coatings. The results show that single-layer dip-coated Yb silicate is a cost-effective CMAS-resistant RE-based EBC.

Fabrication and functional characteristics of micro/nano structures on the RB-SiC surface through nanosecond pulsed laser irradiation

Reaction-bonded silicon carbide (RB-SiC) is gaining increasing attention due to its exceptional mechanical properties contributed by the dispersion of hard silicon carbide (SiC) and silicon (Si), which has been extensively applied in aerospace and automobile industries. Fabrication of micro/nano structures on the RB-SiC surface can endow it some specific functional properties, but conventional manufacturing procedures face challenges due to the intrinsic hard-brittle nature of RB-SiC. In the present study, various micro/nano structures, including dome-like particle structures, micro-cone structures and the spider web-like film, are fabricated on the RB-SiC surface by nanosecond pulsed laser irradiation under different experimental conditions. Comparative experiments are performed to explore the effects of laser power and scanning speed on the microscopic morphology and chemical composition. Consequently, the ablation mechanism is clarified. The formation of micro-cone structures covered by the spider web-like film can result in a wettability transition of the RB-SiC surface from hydrophilicity to superhydrophilicity. In addition, by introducing the spider web-like film, the reflectivity of the RB-SiC surface is increased by an impressive 83% or more in the wavelength range of 200 to 2500 nm. This study provides a method for improving the surface properties of RB-SiC substrates using a laser-based approach, which is anticipated to expand their application prospects as functional materials.

Coextrusion of Reaction‐Bonded Carbides by Robocasting

Coextrusion by robocasting is a suitable process for fabricating multimaterial ceramic structures. Herein, the robocasting process is used to fabricate core–shell structures, combined with subsequent liquid silicon infiltration (LSI). Thus, reaction‐bonded silicon carbide (RBSC), reaction‐bonded boron carbide (RBBC), and reaction‐bonded silicon–boron carbide composites are produced. The LSI process offers the possibility to circumvent high temperatures and pressures used in traditional fabrication. Pastes with high solid loading and necessary carbon content are used in order to combine the robocasting with the subsequent LSI process. The influence of the paste rheology on the sample fabrication of multimaterial core–shell structures of reaction‐bonded carbides is investigated. The key rheological data, such as the viscosities of the combined pastes, are correlated with the observations from the microstructural investigation using scanning electron microscopy. A correlation between the difference in viscosity and the core geometry can be established. Crack formation in the material combination of RBSC and RBBC is found and compared with layered multimaterial structures of reaction‐bonded carbides. Residual stresses, which can be used to explain the crack formation, are investigated using Raman spectroscopy.

Improved mechanical properties of reaction-bonded SiC through in-situ formation of Ti3SiC2

Reaction-bonded SiC is a ceramic with excellent thermal properties, good corrosion resistance and the characteristic of near-net-shape manufacturing. However, the poor fracture toughness of free Si limits the applications of reaction-bonded SiC. In this study, TiC was added to reaction-bonded SiC and reacted with free Si to form Ti3SiC2. The effects of TiC and carbon black on the mechanical properties of reaction-bonded SiC were investigated. The results demonstrated that the in-situ formation of Ti3SiC2 and decrease in the content and size of free Si improved the mechanical properties of reaction-bonded SiC ceramics. The mechanical properties of TiC-added reaction-bonded SiC with 17.5 wt% carbon black were superior to those of TiC-added reaction-bonded SiC with 15 wt% carbon black. Moreover, increasing the TiC content of reaction-bonded SiC with 17.5 wt% carbon black from 0 to 7.5 wt% caused an increase in its bending strength from 183.92 to 424.43 MPa and an increase in fracture toughness from 3.7 to 5.24 MPa m1/2.

Two-step joining of reaction bonded silicon carbide (RBSC) using borosilicate glass

The borosilicate glass was used to join reaction bonded silicon carbide through two steps, namely: laser cladding and low-temperature heat treatment. The wettability and microstructure of the laser cladding glass layer were examined, while joint microstructure and strength were analyzed at various temperatures and times. The results show that the laser cladding layer improved the wetting of glass on the substrate, formed a good interfacial bond, and reduced the joining temperature. The joints primarily consist of the glass phase, the boron-rich phase, and a few crystals. The high-strength joints obtained after heating the joint interface at 950 °C for 30 min had a flexural strength of 250 ± 20 MPa, a 68% improvement compared with direct connection under the same conditions. The joints also exhibit good thermal shock resistance and high-temperature strength. At 400 °C (thermal shock temperature) and 600 °C (test temperature), the residual flexural strengths were 122 ± 25 and 152 ± 12 MPa, respectively.

Formation of Oxides Upon Thermal Debinding and Their Role in Obtaining Reaction-Bonded Silicon Carbide

Formation of Oxides Upon Thermal Debinding and Their Role in Obtaining Reaction-Bonded Silicon Carbide

Environmental stability of additively manufactured siliconized silicon carbide for applications in hybrid energy systems

AbstractA key consideration for the successful operation of hybrid energy systems will be the environmental stability of materials used for their construction, particularly when experiencing service environments containing water vapor at high temperatures. Here, we report results from the characterization of siliconized silicon carbide (Si‐SiC) prepared via binder jet additive manufacturing and reactive silicon melt infiltration after being exposed to environments representative of those in solid oxide fuel cell (SOFC) anodes, and to exhaust gases inside a microturbine operating on natural gas. In both cases, it was found that oxide scales formed on the surface and that these scales were dense, continuous, and well‐bonded to the substrates, although there was evidence of transverse and longitudinal cracking most likely as a result of mismatches in the thermal expansion of the scale and the substrate. Measured values of the thickness of the oxide scale were compared to those predicted by parabolic oxidation kinetics of silicon, but the potential effects of silica volatilization induced by water vapor, and silica reduction when exposed to hydrogen are discussed. The overall results showed that the oxide scale is expected to be protective under the conditions of hybrid power generation systems.

Investigation of the material removal process in in-situ laser-assisted diamond cutting of reaction-bonded silicon carbide

Investigation of the material removal process in in-situ laser-assisted diamond cutting of reaction-bonded silicon carbide

A study on the EDM drilling of reaction-bonded silicon carbide using different electrode materials

Today, there is a growing demand for efficient hole manufacturing technology in many industries such as aeronautics, automotive and nuclear, among others. Thus, the present study deals with the machining of through holes on SiSiC advanced ceramic by using Electrical Discharge Machining (EDM) drilling technology. Since recommendations related to the electrode characteristics and settings parameters are found to be scant for the industrial use of EDM drilling of SiSiC ceramics, this research work comes to cover this gap as it presents a complete study focused on the influence on different electrodes under rough and finish machining conditions. In particular, the influence of four electrodes materials (copper, copper-tungsten, graphite and copper infiltrated graphite) and three different electrode diameters ranging from 2 to 4 mm are investigated. In addition, the rotational speed of the electrode is also analysed. From the experimental results, both electrode material and machining regime, seem to be the most relevant factors of all. In the case of 2 mm diameter electrode, material removal rate (MRR) with Cu electrode was, approximately, 4.5 times higher than that obtained with a C electrode. In fact, it was found that copper electrode rotating at 20 rpm combined with high values of discharge energy (I = 2 A; ti = 70 µs) is the most economical option in terms of production cost and production time, as it gives a high MRR of 0.4754 mm3/min and a minimum electrode wear (EW) value of 7.52%. Moreover, slightly higher values of MRR were achieved for CuC electrode compared to those obtained with C electrode, indicating that the addition of Cu in the electrode contributes to a greater removal of material. However, a value of Ra of 0.37 µm could be obtained by setting low current intensity values (I = 0.5 A; ti = 45 µs) combined with C electrodes and with no rotation.

Effect of Femtosecond Laser Processing Parameters on the Ablation Microgrooves of RB-SiC Composites

Because of the high hardness, brittleness, and anisotropy of reaction-bonded silicon carbide composites (RB-SiC), it is challenging to process high-quality textures on their surfaces. With the advantages of high processing accuracy and low processing damage, femtosecond laser processing is the preferred technology for the precision processing of difficult-to-process materials. The present work used a femtosecond laser with a linear scanning path and a spot diameter of 18 µm to process microgrooves on RB-SiC. The influence of different processing parameters on the microgroove profile, dimensions, and ablation rate (AR) was investigated. The ablation width Wa and average ablation depth Da of microgrooves were evaluated, and the various patterns of varying processing parameters were obtained. A model for Wa prediction was developed based on the laser fluence within the finite length (FL). As a result, the experimental values were distributed near the prediction curve with a maximum error of 20.4%, showing an upward trend of gradually decreasing increments. For a single pass, the AR value was mainly determined by the laser energy, which could reach the scale of 106 μm3/s when the laser energy was greater than 50 μJ. For multiple passes, the AR value decreased as the number of passes increased and it finally stabilized. The above research will provide theoretical and experimental support for the high-quality and efficient processing of RB-SiC surface textures.

Formation of Laser-Induced Periodic Surface Structures on Reaction-Bonded Silicon Carbide by Femtosecond Pulsed Laser Irradiation

Reaction-bonded silicon carbide (RB-SiC) is an excellent engineering material with high hardness, stiffness, and resistance to chemical wear. However, its widespread use is hindered due to the properties mentioned above, making it difficult to machine functional surface structures through mechanical and chemical methods. This study investigated the fundamental characteristics of laser-induced periodic surface structures (LIPSSs) on RB-SiC via femtosecond pulsed laser irradiation at a wavelength of 1028 nm. Low-spatial-frequency LIPSS (LSFL) and high-spatial-frequency LIPSS (HSFL) formed on the surface along directions perpendicular to the laser polarization. SiC grains surrounded by a large amount of Si show a reduced threshold for LIPSS formation. By varying laser fluence and scanning speed, HSFL–LSFL hybrid structures were generated on the SiC grains. Transmission electron microscopy observations and Raman spectroscopy were carried out to understand the formation mechanism of the hybrid LIPSS. A possible mechanism based on the generation of multiple surface electromagnetic waves due to the nonlinear response of SiC was proposed to explain the hybrid structure formation. Furthermore, the direction of laser scanning with respect to laser polarization affects the uniformity of the generated LIPSS.