Reaction Bonded Silicon Carbide Ceramics Research Articles

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.

A Novel Grain-Based DEM Model for Evaluating Surface Integrity in Scratching of RB-SiC Ceramics

A novel grain-based DEM (Discrete Element Method) model is developed and calibrated to simulate RB-SiC (Reaction-Bonded Silicon Carbide) ceramic and associated scratching process by considering the bonded SiC and Si grains and cementitious materials. It is shown that the grain-based DEM model can accurately identify transgranular and intergranular cracks, and ductile and brittle material removal modes. It also shows that by increasing the scratching speed or decreasing the depth of cut, the maximum depth of subsurface damage decreases, because the scratching force is relatively large under the low scratching speed or large depth of cut that facilitates the occurrence of transgranular cracks, large grain spalling from the target surface and the propagation of median cracks into the target subsurface. It has further been found that increasing the cutting-edge radius can enhance the target ductile machinability and reduce the target subsurface damage.

Direct ink writing of reaction bonded silicon carbide ceramics with high thermal conductivity

Silicon carbide (SiC) ceramic is one of the most used ceramic materials due to its excellent mechanical and thermal properties but the cost is high in production. Three-dimensional (3D) manufacturing of ceramic materials provides the possibility to fabricate ceramic components with unique geometry structures and can save time and cost in producing form and function parts. In this paper, reaction bonded silicon carbide (RBSC) ceramic was fabricated through direct ink writing (DIW) technology. Reaction bonded silicon carbide (RBSC) means infiltration of carbon containing porous green parts with melting silicon, leading to form β-SiC. Remaining pores are filled by residual free silicon. Silicon carbide (SiC) based inks with different carbon black content at solid content of 36 vol% were prepared. The inks consisted of silicon carbide powder as inner filler, carbon black powder and low content sodium alginate as the binder. The effect of carbon black content on rheological behavior was studied. The results showed that the carbon black content played an important role in adjusting the viscosity, modulus and yield point. With the increasing carbon black content, shrinkage of the printed green parts decreased. When the carbon black content reached 20 wt%, the final DIW RBSC ceramics had low residual Si content. The maximum density, flexural strength and thermal conductivity were 2.91 g/cm3, 229 MPa, and 132 W/(m·K), respectively. This study shows a bright prospect of this innovated 3D printing technology for flexibly producing complex and net-shaped RBSC ceramic parts.

SiC ceramic mirror fabricated by additive manufacturing with material extrusion and laser cladding

As the aperture of the optical component increases, the integrated design of the silicon carbide optical component and the support structure will lead to a more complex structure of the silicon carbide optical component, which is difficult to achieve with traditional ceramic molding and sintering technology. In this work, a novel shaping method for the fabrication of reaction bonded silicon carbide ceramic substrate was investigated. Here, four kinds of mixture consisting of silicon carbide, carbon black powder, and organic binder with different solid loading were developed by varying the content of the lubricant paraffin wax (PW) and printed by material extrusion (MEX). The effects of solid loading on the rheological properties of mixtures, thermal expansion behavior, and morphology of the samples after debinding were studied. Similarly, two kinds of materials were prepared with silicon carbide to carbon black ratios of 50: 50 and 60: 40 under optimal solid loading, and their microstructure was analyzed and compared. The results show that reaction bonded silicon carbide ceramics with a flexural strength of 310.41 ± 39.32 MPa and a modulus of elasticity of 346.3 ± 22.80 GPa can be obtained by MEX and reactive sintering when the ratio of silicon carbide to carbon black is 60:40 and at an optimum solid loading (~60 vol%). Subsequently, the dense glass layer was prepared on the surface of 3D printed SiC by laser cladding. After polishing and plating with Ag film, it shows good reflection. In the range of 500–800 nm, the average reflectivity is higher than 97%. The laser cladding Si layer acts as a transition layer, which improves the wettability between the glass melt and the substrate and weakens the decomposition of SiC. This work provides a reference for the preparation of high precision, high strength, and high density SiC ceramic mirror by material extrusion and laser cladding.

Surface Morphology Evaluation and Material Removal Mechanism Analysis by Single Abrasive Scratching of RB-SiC Ceramics

Reaction-Bonded Silicon Carbide (RB-SiC) ceramics possessing excellent mechanical and chemical properties, whose surface integrities have an essential effect on their performance and service life, have been widely used as substrates in the core parts of aerospace, optics and semiconductors industries. The single abrasive scratching test is considered as the effective way to provide the fundamental material removal mechanisms in the abrasive lapping and polishing of RB-SiC ceramics for the best surface finish. In this study, a novel single abrasive scratching test with an increasing scratching depth has been properly designed to represent the real abrasive lapping and polishing process and employed to experimentally investigate the surface integrity regarding different scratching speeds. Three typical and different material removal stages, including the ductile mode, ductile–brittle transition mode and brittle mode, can be clearly distinguished and it is found that in the ductile material removal stage by increasing the scratching speed would inhibit the plastic deformation and improve its surface integrity. It is also found that in the ductile–brittle transition and brittle material removal stages, to increase the scratching speed would inhibit the plastic deformation due to the fast scratching speed that limits the time of plastic deformation on the target, but it also results in the increased length of lateral cracks with the increased scratching speed which can reflect that the size of brittle chips, like brittle fractures and large grain fragmentations, increases as the scratching speed increases. It can provide the references for the optimization of the abrasive lapping and polishing of RB-SiC ceramics with high efficiency and surface quality.

Improvement of toughness of reaction bonded silicon carbide composites reinforced by surface-modified SiC whiskers

To improve the reliability, especially the toughness, of the reaction bonded silicon carbide (RBSC) ceramics, silicon carbide whiskers coated with pyrolytic carbon layer (PyC-SiCw) by chemical vapor deposition (CVD) were introduced into the RBSC ceramics to fabricate the SiCw/RBSC composites in this study. The microstructures and properties of the PyC-SiCw/RBSC composites under different mass fraction of nano carbon black and PyC-SiCw were investigated methodically. As a result, a bending strength of 550 MPa was achieved for the composites with 25 wt% nano carbon black, and the residual silicon decreased to 11.01 vol% from 26.58 vol% compared with the composite of 15 vol% nano carbon black. The fracture toughness of the composites reinforced with 10 wt% PyC-SiCw, reached a high value of 5.28 MPa m1/2, which increased by 39% compared to the RBSC composites with 10 wt% SiCw. The residual Si in the composites deceased below to 7 vol%, resulting from the combined actively reaction of nano carbon black and PyC with more Si. SEM and TEM results illustrated that the SiCw were protected by PyC coating. A thin SiC layer formed of outer surface of whiskers can provide a suitable whisker-matrix interface, which is in favor of crack deflection, SiCw bridging and pullout to improve the bending strength and toughness of the SiCw/RBSC composites.

Environment-Friendly Preparation of Reaction-Bonded Silicon Carbide by Addition of Boron in the Silicon Melt.

Reaction-bonded silicon carbide ceramics were sintered by infiltration of Si and B–Si alloy under an argon atmosphere at different temperatures. The element boron was added to the silicon melt to form a B–Si alloy first. The mechanical properties of samples were improved by infiltration of the B–Si melt. The samples infiltrated with the Si-only melt were found to be very sensitive to experimental temperature. The bending strengths of 58.6 and 317.0 MPa were achieved at 1530 and 1570 °C, respectively. The sample made by infiltration of B–Si alloy was successfully sintered at 1530 °C. The relative density of the sample was more than 90%. The infiltration of B–Si alloy reduced the sintering temperature and the bending strength reached 326.9 MPa. The infiltration mechanism of B–Si alloy is discussed herein.

Robocasting of reaction bonded silicon carbide/silicon carbide platelet composites

Pastes with a varying amount of uncoated SiC platelets (SiCplatelets) for the fabrication of reaction bonded silicon carbide (RBSC) were developed and the effect of the anisotropic particles on the microstructure and mechanical properties of the fabricated RBSC/SiCplatelets composites was studied. During printing the platelets align in printing direction due to shear forces. This texturization was confirmed by image analysis and EBSD measurement.The bending strength and the fracture toughness of about 470 MPa and 2.7 MPam1/2, respectively, did not change significantly after the addition of uncoated platelets, but showed comparable values according to the literature data for RBSC ceramics. Hardness and Young's modulus (17 GPa and 380 GPa) were also comparable to traditionally fabricated RBSC ceramics and showed a slight increase after the addition of platelets. SEM analysis of the fracture surfaces of the fabricated composites showed no pull-out and nearly no crack deflection, which may explain the constant values of the mechanical properties. Further work is therefore aimed at developing the paste filled with coated platelets.Although the influence of the uncoated platelets was small, the technological feasibility of producing textured RBSC/SiCplatelets composites using robocasting was demonstrated and the possibility to generate complex structures was successfully shown.

Preparation and properties of porous reaction-bonded SiC ceramic using Si3N4 as silicon source

In the traditional porous reaction-bonded silicon carbide (RBSC) ceramic, the phenomenon of residual silicon usually happens due to the usage of monatomic silicon as reactant, which greatly weakens its high-temperature properties, as well as corrosion resistance. In this paper, Si3N4 was successfully utilized as silicon source for the preparation of porous RBSC ceramics. Only SiC phase in the final bulks was detected by X-ray, indicating the achievement of avoiding residual silicon. There were homogeneous and isotropous pores with 48.3% of porosity for as-acquired RBSC ceramic. Its average pore size was ∼1.6 μm, while the pore throat size was less than 1 μm. Compared with porous oxide-bonded SiC ceramic, porous RBSC ceramic showed superiority in N2 permeability (217 m3/(m2·h·bar)), as well as flexural strength at normal temperature (35.5 ± 2.3 MPa), and high temperature of 1000 °C (21.2 ± 1.7 MPa). Moreover, porous RBSC could keep intact after exposing in boiling solutions of 10 wt% H2SO4 and 1 wt% NaOH for 12 h, indicating its chemical stability in the acid and alkaline environment.

Enhanced strength and toughness of silicon carbide ceramics by graphene platelet-derived laminated reinforcement

To exploit the application of silicon carbide in complex-shaped and large-scale ceramic components, graphene platelet (GPL) was chosen as the reinforcement to develop silicon carbide ceramics by reactive sintering at 1700 °C. The effects of GPL content on the microstructure, phase composition and mechanical behaviors of reaction bonded silicon carbide ceramics were studied. Bulk density of the composites decreased with the increase of GPL contents because of the agglomeration of GPL. During reactive sintering, the GPL reacted with molten silicon to form laminated reinforcement, which brought about some toughening mechanisms including crack bridging, reinforcement pullout and reinforcement delamination. At the GPL content of 1.0 wt%, the flexural strength and fracture toughness of the composites reached the peak values of 436 MPa and 5.7 MPa m 1/2 , respectively. Thus, this work provides a path to prepare high-performance silicon carbide ceramics by reactive sintering and graphene platelet. • Graphene platelet was chosen in the reactive sintering of SiC ceramics. • Graphene reacted with molten silicon to produced laminated reinforcement. • Step-by-step fracture by graphene improved fracture toughness of SiC ceramics.

Nanomechanical characterization of RB-SiC ceramics based on nanoindentation and modelling of the ground surface roughness

Reaction bonded silicon carbide (RB-SiC) ceramics are the primary structure and mold materials for the optical industry and mostly are machined by means of ultra-precision grinding to achieve a satisfactory surface quality. However, it is not easy to attain the theoretical prediction of surface quality, particularly surface roughness, because of different mechanical characterization of Si/SiC phases inside the RB-SiC ceramics. In this work, the nanoindentation tests were performed to investigate the nanomechanical characterization of individual phase inside the RB-SiC ceramics. On the basis of the nanoindentation results of RB-SiC, a theoretical model was established to predict surface roughness in the ultra-precision grinding process, which considered the different removal mechanisms of Si matrix and SiC particles. The comparison of the prediction results of existing and novel models and single-factor experimental results shows that the novel model was well consistent with the experiment.

Mechanical properties and microstructure of reaction sintering SiC ceramics reinforced with graphene-based fillers

To improve the fracture toughness and bending strength of reaction sintering SiC ceramics, graphene oxide (GO) and reduced graphene oxide (rGO) were selected as fillers to develop reinforced SiC ceramic composites by reactive sintering in the current work. Different amounts (0.5, 1.0, 1.5, or 3.0 wt.%) of graphene-reinforced reaction-bonded silicon carbide (RBSC) composites were fabricated. The mechanical behaviors of the materials were evaluated as a function of the type of graphene source and graphene content. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis showed that graphene was maintained after reactive sintering by liquid infiltration of molten silicon. Both the fracture toughness and bending strength of the RBSC increased with employing graphene-based additives. GO showed the most significant positive effects on improving mechanical performance of RBSC ceramics. The highest fracture toughness of 3.6 MPa m1/2 was obtained at 1.5 wt.% of GO addition. It was 33% higher than that of RBSC without graphene. The highest bending strength corresponded to the composite reinforced with GO content of 1.0 wt.%. It was about 58% higher than that of RBSC ceramic. The relation between phase content and mechanical properties was discussed. The main toughening mechanism was sheet pullout/debonding and the distribution of graphene along grain boundaries.

A New Grinding Force Model for Micro Grinding RB-SiC Ceramic with Grinding Wheel Topography as an Input.

The ability to predict the grinding force for hard and brittle materials is important to optimize and control the grinding process. However, it is a difficult task to establish a comprehensive grinding force model that takes into account the brittle fracture, grinding conditions, and random distribution of the grinding wheel topography. Therefore, this study developed a new grinding force model for micro-grinding of reaction-bonded silicon carbide (RB-SiC) ceramics. First, the grinding force components and grinding trajectory were analysed based on the critical depth of rubbing, ploughing, and brittle fracture. Afterwards, the corresponding individual grain force were established and the total grinding force was derived through incorporating the single grain force with dynamic cutting grains. Finally, a series of calibration and validation experiments were conducted to obtain the empirical coefficient and verify the accuracy of the model. It was found that ploughing and fracture were the dominate removal modes, which illustrate that the force components decomposed are correct. Furthermore, the values predicted according to the proposed model are consistent with the experimental data, with the average deviation of 6.793% and 8.926% for the normal and tangential force, respectively. This suggests that the proposed model is acceptable and can be used to simulate the grinding force for RB-SiC ceramics in practice.

Corrosion behaviors of porous reaction-bonded silicon carbide ceramics incorporated with CaO

Reaction-bonded SiC (RBSC) porous ceramics were fabricated at 1450 °C in air by incorporating CaO using ZrO2 as sintering aids, activated carbon as pore-forming agent, and mullite fibers as reinforcing agent. The effects of CaO content on the properties of the porous RBSC ceramics were studied. Corrosion behaviors of the prepared RBSC porous ceramics in different environments were also investigated. The optimal open porosity, bending strength, average pore size and gas permeability of the ceramics with 0.5% CaO were 40%, 22.5 MPa, 42.9 µm, and 2100 m3/m2 h kPa, respectively. A well-developed neck reaction-bonded by calcium zirconium silicate (Ca3ZrSi2O9) was identified. The porous RBSC ceramics exhibited excellent corrosion resistance in acid and basic solutions. The anti-oxidation temperature of the porous RBSC ceramics could reach 1200 °C in air. The RBSC ceramics maintained the bending strength of 17.5 MPa after 60 cold-hot cycles in air (0–800 °C). The porous RBSC ceramics also exhibited relatively good corrosion resistance in molten salts (NaCl, Na2SO4 and CaCl2). Melten NaOH can aggravate the reaction by breaking the SiO2 layers on the SiC surface. Overall, these findings offer significant insights into expanding the applications porous RBSC ceramics incorporated with CaO.

Experimental investigation on electrical discharge diamond grinding of RB-SiC ceramics

The reaction-bonded silicon carbide (RB-SiC) ceramics are very difficult to be machined by conventional techniques. In this work, a hybrid process termed electrical discharge diamond grinding (EDDG) was applied to the precision grinding of RB-SiC ceramics considering its weak electrical conductivity. Focus of investigation was especially placed on the effects of grit sizes and polarities of grinding wheel on the surface quality. The machined surface texture and roughness were measured by confocal scanning laser microscope. The surface texture topography and cross-section profile at different grit sizes and polarities were analyzed. The results show that the dominant state of grinding or EDM decides surface texture of machined surface and consequently affects the surface roughness. The surface morphology and subsurface damage were measured by scanning electron microscopy and energy dispersive spectrometer (EDS). The influence of grit sizes and polarities of grinding wheel was focused on the resolidified zone of the machined surface. The material migration phenomenon was found. The subsurface damage was also analyzed by detecting the polished cross-sections, and the depth of subsurface was determined by analyzing the element distribution with EDS spectrums. At last, the formation mechanism of machined surface and the effects of grit sizes and polarities of grinding wheel on machined surface quality were discussed from the viewpoint of discharge energy based on EDM theory.

Experimental investigation on the surface and subsurface damages characteristics and formation mechanisms in ultra-precision grinding of SiC

Surface and subsurface damages appear inevitably in the grinding process, which will influence the performance and lifetime of the machined components. In this paper, ultra-precision grinding experiments were performed on reaction-bonded silicon carbide (RB-SiC) ceramics to investigate surface and subsurface damages characteristics and formation mechanisms in atomic scale. The surface and subsurface damages were measured by a combination of scanning electron microscopy (SEM), atomic force microscopy (AFM), raman spectroscopy, and transmission electron microscope (TEM) techniques. Ductile-regime removal mode is achieved below critical cutting depth, exhibiting with obvious plow stripes and pile-up. The brittle fracture behavior is noticeably influenced by the microstructures of RB-SiC such as impurities, phase boundary, and grain boundary. It was found that subsurface damages in plastic zone mainly consist of stacking faults (SFs), twins, and limited dislocations. No amorphous structure can be observed in both 6H-SiC and Si particles in RB-SiC ceramics. Additionally, with the aid of high-resolution TEM analysis, SFs and twins were found within the 6H-SiC closed packed plane, i.e., (0001). At last, based on the SiC structure characteristic, the formation mechanisms of SFs and twins were discussed, and a schematic model was proposed to clarify the relationship between plastic deformation-induced defects and brittle fractures.

Effects of Electricity Parameters on Surface Quality of Reaction Bonded Silicon Carbide Ceramic with Electrical Discharge Diamond Grinding

With some conductivity and low grinding affectivity, a hybrid machining process termed electrical discharge diamond grinding (EDDG) is applied to the precision machining of reaction bonded silicon carbide (RB-SiC) ceramic. As there is electrical spark in the hybrid machining process, the electrical parameters are varied to explore their effects on the surface quality of RB-SiC ceramic with EDDG. In this paper, the experiments of different polarity and gap voltage with EEDG were investigated, and the microstructure and surface roughness on the machined surface of RB-SiC ceramic were analyzed. The surface morphology and micro-cracks were examined with a scanning electron microscope, and the surface roughness was measured with a confocal scanning laser microscope. It is found that surface roughness initially increases and then decreases with increase of the gap voltages and is higher with negative polarity than that with positive polarity. The micromorphology Micro-cracks were observed on the surface machined and are outstanding in re-solidified zone with EDDG.

반응소결 탄화규소 세라믹스의 열물성과 기계적 특성에 미치는 SiC 크기의 영향

Abstract RBSC (reaction-bonded silicon carbide) represents a family of composite ceramics processed by infiltratingwith molten silicon into a skeleton of SiC particles and carbon in order to fabricate a fully dense body of silicon car-bide. RBSC has been commercially used and widely studied for many years, because of its advantages, such as rela-tively low temperature for fabrication and easier to form components with near-net-shape and high relative density,compared with other sintering methods. In this study, RBSC was fabricated with different size of SiC in the raw mate-rial. Microstructure, thermal and mechanical properties were characterized with the reaction-sintered samples in order toexamine the effect of SiC size on the thermal and mechanical properties of RBSC ceramics. Especially, phase volumefraction of each component phase, such as Si, SiC, and C, was evaluated by using an image analyzer. The relationshipbetween microstructures and physical properties was also discussed.Keywords: RBSC (reaction-bonded silicon carbide), SiC size, Microstructures, Thermal properties, Mechanical properties