Reaction-bonded Silicon Carbide Research Articles

Residual thermal stress analysis of SiC joint by polysiloxane silicon resin YR3187

Reaction-bonded silicon carbide was joined using a polysiloxane silicon resin YR3187. Residual thermal stress distribution in joint structure was calculated by finite element analysis method. Factors influencing the distribution of residual thermal stress, including joining temperature, thickness of join layer, and presence of crack in join layer, were studied. The simulated results were compared with actual joint strength. It is showed that in determining the joining temperature, the pyrolysis procedure of silicon resin should be taken into consideration; in addition, the reasonable thickness of the join layer and the reduction of cracks in join layer are important to obtain higher joint strength.

Experimental investigation on material migration phenomena in micro-EDM of reaction-bonded silicon carbide

Material migration between tool electrode and workpiece material in micro electrical discharge machining of reaction-bonded silicon carbide was experimentally investigated. The microstructural changes of workpiece and tungsten tool electrode were examined using scanning electron microscopy, cross sectional transmission electron microscopy and energy dispersive X-ray under various voltage, capacitance and carbon nanofibre concentration in the dielectric fluid. Results show that tungsten is deposited intensively inside the discharge-induced craters on the RB-SiC surface as amorphous structure forming micro particles, and on flat surface region as a thin interdiffusion layer of poly-crystalline structure. Deposition of carbon element on tool electrode was detected, indicating possible material migration to the tool electrode from workpiece material, carbon nanofibres and dielectric oil. Material deposition rate was found to be strongly affected by workpiece surface roughness, voltage and capacitance of the electrical discharge circuit. Carbon nanofibre addition in the dielectric at a suitable concentration significantly reduced the material deposition rate.

Carbon nanofiber assisted micro electro discharge machining of reaction-bonded silicon carbide

Carbon nanofiber assisted micro electro discharge machining was proposed and experiments were performed on reaction-bonded silicon carbide. The changes in electro discharging behavior, material removal rate, electrode wear ratio, electrode geometry, spark gap, surface finish, surface topography and surface damage with carbon nanofiber concentration were examined. It has been found that the addition of carbon nanofiber not only improves the electro discharge frequency, material removal rate, discharge gap, but also reduces the electrode wear and electrode tip concavity. Bidirectional material migrations between the electrode and the workpiece surface were detected, and the migration behavior was strongly suppressed by carbon nanofiber addition. Adhesion of carbon nanofibers to the workpiece surface occurs, which contributes to the improvement of electro discharge machinability. These findings provide possibility for high-efficiency precision manufacturing of microstructures on ultra-hard ceramic materials.

Material Analysis of Coated Siliconized Silicon Carbide (SiSiC) Honeycomb Structures for Thermochemical Hydrogen Production.

In the present work, thermochemical water splitting with siliconized silicon carbide (SiSiC) honeycombs coated with a zinc ferrite redox material was investigated. The small scale coated monoliths were tested in a laboratory test-rig and characterized by X-ray diffractometry (XRD) and Scanning Electron Microscopy (SEM) with corresponding micro analysis after testing in order to characterize the changes in morphology and composition. Comparison of several treated monoliths revealed the formation of various reaction products such as SiO2, zircon (ZrSiO4), iron silicide (FeSi) and hercynite (FeAl2O4) indicating the occurrence of various side reactions between the different phases of the coating as well as between the coating and the SiSiC substrate. The investigations showed that the ferrite is mainly reduced through reaction with silicon (Si), which is present in the SiSiC matrix, and silicon carbide (SiC). These results led to the formulation of a new redox mechanism for this system in which Zn-ferrite is reduced through Si forming silicon dioxide (SiO2) and through SiC forming SiO2 and carbon monoxide. A decline of hydrogen production within the first 20 cycles is suggested to be due to the growth of a silicon dioxide and zircon layer which acts as a diffusion barrier for the reacting specie.

1.5m量级SiC陶瓷素坯凝胶注模成型工艺

AΦ1.5msilicon carbide(SiC)ceramic green body with a lightweight structure was prepared by gel casting method.The effects of Particle Size Distribution(PSD),solid loading and milling time on the SiC suspension were studied systematically.Then the microstructure and bending strength of the SiC green body,and the mechanical and thermal properties of Reaction Bonded SiC(RB-SiC)were measured.The results show that the 65% solid loading SiC slurry with good flow properties is prepared by optimum PSD in a stable dispersion condition.The slurry viscosity of SiC increases rapidly with the solid loading.However,the apparent viscosity of SiC slurry reduces and then increases with the milling time.Moreover,the SiC slurry was injected into a mould,and aΦ1.5m SiC ceramic green body was obtained.The ceramic green body after degreasing has a uniform interior structure and a bending strength of 24.6MPa.

반응소결 탄화규소의 다양한 α-SiC 조성에 따른 기계적 특성과 전기저항 특성에 관한 연구

저저항 Si-SiC 소결체 제조를 위해 <TEX>${\alpha}$</TEX>-SiC에서 조성과 C의 양을 변화시키면서 반응소결 특성을 고찰하였다. 시료준비는 정수압으로 성형체를 제조하였고, 용융Si 반응소결을 통해 시험편을 준비하였다. 반응소결체의 미세구조, 기계적 특성 및 전기저항 분석 결과 용융Si과 반응 후 미립의 <TEX>${\beta}$</TEX>-SiC가 생성되었고, 치밀한 소결체를 형성하였다. 미립 <TEX>${\beta}$</TEX>-SiC 생성량은 카본 양 에 따라 증가하였다. 그리고 C함량 10wt%이내에서 기계 R전기저항특성은 입도조성 영향이 크고 카본 함량 10wt%이상에서는 상전이 반응의 영향이 큼을 알 수 있었다. For the manufacture of low resistance Si-SiC composite, the properties of reaction sintering in the green body of various mixed <TEX>${\alpha}$</TEX>-SiC powder size with the various carbon contents from 0wt% to 20wt% were investigated. The samples preparation was green body by CIP method under this condition, molten silicon infiltration process was conducted to reaction bonded silicon carbide. the results of sintered density, 3-point bending strength and resistance of analysis showed that varied carbon and silicon melt reacted to convert to fine <TEX>${\beta}$</TEX>-SiC particle and the structure was changed to dense material. The amount of fine <TEX>${\beta}$</TEX>-SiC particle was gradually increased as carbon content increase. According to mixed composite, it's mechanical and specific resistivity properties was strongly influenced by carbon content within 10wt% more then carbon content 10wt% was strongly influenced by phase transition.

Fabrication and characterization of reaction-bonded silicon carbide with poly(methyl methacrylate) as pore-forming agent

Abstract Reaction-bonded silicon carbide (RBSC) ceramics were prepared by liquid silicon infiltration at 1600 °C using a carbon biscuit. The green body was made by slip casting a stabilized carbon powder slurry, followed by pyrolysis in a vacuum furnace at 1000 °C for 2 h; the density of the biscuit (ρb) was controlled using poly(methyl methacrylate) (PMMA) powder as pore former in mass proportion from 30% to 50% in 5 percentage point intervals. The particle size of the PMMA had significant effects on the microstructure, distribution of residual silicon, and the mechanical properties of the ceramic. For 40 mass% PMMA with d50=1.17 μm and d50=0.51 μm, ρb was 0.81 and 0.82 g/mL, with corresponding biscuit porosities of 51% and 50%, which gave peak values of both RBSC ceramic density of 3.07 and 3.10 g/mL, and flexural strength of 741 and 794 MPa, respectively. XRD analysis showed that the main phase was β-SiC, with a small quantity of α-SiC. Using PMMA with d50=0.51 μm, a small quantity of residual Si was well dispersed with grain size

Reaction-bond sintering of C/SiC functionally graded nanostructured materials (FGNMs)

In this study, bulk C/SiC functionally graded nanostructured materials (FGNMs) having a compositional gradient from carbon (C) to silicon carbide (SiC) were obtained by applying the powder-stacking method under pressureless sintering condition. During the sintering process, the reaction-bonded SiC was formed in the presence of pure silicon (Si) which led to increase in the density and strength of the FGNMs. At the sintering stage, the compacted bodies were heated at 1525°C for 2h in an argon atmosphere. Results showed that the number of graded layers had a marked effect on the microstructure and properties of the sintered C/SiC FGNMs. With increasing number of graded layers, the bend strength of the samples improved significantly. Moreover, SEM micrographs illustrated that the formation of SiC nanorods between adjacent particles improved the bending strength of the samples.

Effect of carbon particle and carbon fiber on the microstructure and mechanical properties of short fiber reinforced reaction bonded silicon carbide composite

Variation of microstructure and mechanical behavior was investigated with the content increase of carbon particles and carbon fiber in the reaction bonded silicon carbide composites. The composites were prepared by slip casting and liquid silicon infiltration. The bulk density is raised with the increase of carbon black due to the formation of fine β-SiC particles. The flexural strength increases for the reduction of residual Si and the formation of SiC framework; whereas a very high carbon content reduces the flexural strength. The fracture toughness is controlled by the contents of carbon particle and carbon fiber. Thus, fiber debonding, fiber pullout and crack deflection are considered as the main toughening mechanisms. Annealing treatment can effectively improve both the flexural strength and fracture toughness. An increase by 49% of fracture toughness is obtained. A series of structural models are proposed to illustrate the structure changes of carbon fiber.

Effect of Different Dielectric Fluids on Micro EDM of Low Conductivity Ceramic Material RB-SiC

The machining characteristics of reaction bonded silicon carbide (RB-SiC) in micro electrical discharge machining process were studied by using EDM oil, deionized water, and graphite fiber mixed EDM oil as the dielectric fluids. The process performances were measured in terms of material removal rate, surface roughness and surface topography. The effect of deionized water on SUS 304 also was tried and compared with that on RB-SiC. It was found that when graphite fiber mixed EDM oil was used, higher material removal rate, better surface finish and smoother surface topography were obtained compared to that pure EDM oil and deionized water on RB-SiC. Deionized water could produce better form accuracy, however, electrolytic corrosion occurred and small pits were formed around the machining area of RB-SiC. In contrast, electrolytic corrosion was insignificant for SUS 304.

Wear-mechanical properties of filler-added liquid silicon infiltration C/C–SiC composites

A carbon fiber reinforced silicon carbide matrix (C/C–SiC) composites material was manufactured by introducing a filler into the liquid silicon infiltration (LSI) process. The filler consisted of Si:Carbon black=1:1 mixed with a phenol resin. Use of the filler resulted in a negligible reduction in the residual free Si of approximately 0.7% but increased 15% of reacted SiC amount. Dilatometer and X-ray diffraction (XRD) evaluations also confirmed improved formation of reaction-bonded silicon carbide (SiC) in the matrix. The wear rate was decreased more than 2.5-fold, indicating significantly improved wear-resistance properties. However, flexural strength gradually decreased and fiber damage was observed in fracture surface with increases in filler content.

Carbon fiber/reaction-bonded carbide matrix for composite materials – Manufacture and characterization

Abstract The processing of self-healing ceramic matrix composites by a short time and low cost process was studied. This process is based on the deposition of fiber dual interphases by chemical vapor infiltration and on the densification of the matrix by reactive melt infiltration of silicon. To prevent fibers (ex-PAN carbon fibers) from oxidation in service, a self-healing matrix made of reaction bonded silicon carbide and reaction bonded boron carbide was used. Boron carbide is introduced inside the fiber preform from ceramic suspension whereas silicon carbide is formed by the reaction of liquid silicon with a porous carbon xerogel in the preform. The ceramic matrix composites obtained are near net shape, have a bending stress at failure at room temperature around 300 MPa and have shown their ability to self-healing in oxidizing conditions.

Zirconia reinforced reaction bonded silicon carbide composites: Microstructure and mechanical properties

Nano-sized zirconia particles were dispersed in a SiC/C suspension to examine the particle influence on microstructure and mechanical properties on the resulting composite. The ZrO2/reaction bonded SiC composite was produced by a combination of slip casting and liquid silicon infiltration. By dispersing zirconia particles into the matrix, the gowth of β-SiC was inhibited and the size of residual silicon was reduced. This result led to an increase of flexural strength with reinforcement ranging from 0 to 20wt.%. Compared with the monolithic RBSC ceramics, the fracture toughness was steadily improved, reaching the peak value of appropriate 4.6MPam1/2 at the zirconia fraction of 25wt.%. The XRD analysis revealed the phase transformation occurred on the fracture surface of the composites. Thus, the transformation of zirconia and the crack deflection are considered as the main toughening mechanisms.

Grinding Characteristics of Reaction Bonded Silicon Carbide

Surface topography,surface residual stress and bending strength of RBSiC ground using diamond wheel were studied.Grinding RBSiC is removed mainly by brittle fracture and lightly by ductile cutting.With the increase of down feed,surface roughness Ra increases.Burnishing with no down feed can improve the Rain some way.With increasing down feed,the compressive residual stress decreases because of an inadequately cooling effect.Compare with the specimens grounded using 0.9 μm/s,those using down feed of 1.35 μm/s have worse surface quality.Considering both the processing efficiency and the surface quality,the optimum parameters are as follow: 0.9 μm/s down feed,2.1 r/min work table rotational speed and 1 min burnishing.

The Effects of Different Slurry on the Joining Characteristics of SiC Green Body

Experiments were carried out to join reaction-bonded silicon carbide (RBSC) ceramic in green body. SiC green bodies were fabricated by gel-casting method. The slurries for joint were prepared by different grain size of SiC. The results indicate the solid loading and the grain size of SiC influence the strength of welding. There is no clear welding interface between the two substrates in an appropriate solid volume loading and grain size. The average bending strength of welding after sintering can reach 300MPa. SEM was used to observe the cross-section morphology and microstructure of binding sites. The test result shows that its microstructure is similar to the RB-SiC ceramic. The mechanical properties of binding sites were tested. The result shows a desirable mechanical property.

Study of Resistance Characteristics of Silicon Carbide Resistor Materials

Experimental program and preparation technology of highly densified reaction bonded silicon carbide resistance materials with different resistivity were investigated by using alumina or silicon nitride as aids for improving of the volume resistivity. The microstructure of the materials was observed by scanning electron microscope. According to the experimental results, the resistivity of the material could be controlled by the particle size and the content of the aids. Besides, alumina could reduce silicon penetration and increase resistivity greatly, and 10wt.% of alumina could satisfy the requirement of resistance. In addition, different particle size of matrix materials had a great impact on the resistivity. Compared with the coarse silicon carbide, the room temperature resistivity value by using the fine silicon carbide could increases for six times.

Random chopped fibers in reaction bonded SiC composite: Morphology, etching and reinforcing properties

Random chopped fibers were introduced into SiC/C slurry to improve the mechanical behaviors of reaction bonded SiC ceramics. The distribution, morphology and chemical properties of the siliconized carbon fiber were investigated. The effect of fiber fraction on mechanical behaviors of the reaction bonded silicon carbide composite was studied. The siliconization reaction led to a dense layer of nano and micron SiC particles on the fiber surface. Based on the morphology changes in the acid etching test, a structural model of the siliconized fiber was proposed. The fracture toughness and the flexural strength of the composite were improved by the random chopped fiber, reaching the peak values of 5.1MPam0.5 and 416MPa, respectively, at the fiber fraction of 30vol.%.

Effects of random chopped fiber on the flexural strength and toughness of reaction bonded silicon carbide composite

Chopped carbon fibers were introduced into the SiC/C suspensions to enhance the mechanical behaviors of reaction bonded silicon carbide ceramics. The effects of fiber fraction on the flexural strength and fracture toughness were investigated. No preferred fiber orientation was observed on the fracture surface of the green body. This implies a homogeneous dispersion of chopped fiber in the composite. XRD analysis indicates a complete siliconization of both carbon particles and carbon fiber during liquid silicon infiltration. The flexural strength and fracture toughness increase with chopped fiber ranging from 10vol.% to 30vol.%. This improvement derives from the fiber pullout, fiber debonding as well as crack deflection. The consequent decline at fiber fraction of 40vol.% is resulted from the siliconization of chopped fiber and the increase of residual silicon.

Morphology of SiC Whisker in Whisker Reinforced Reaction Bonded SiC Composite

SiC whisker was introduced into reaction bonded silicon carbide to produce high performances composite by slip casting and reaction sintering. This study aimed at morphology of SiC whisker in the reaction bonded silicon carbide ceramics. The whisker was homogeneously dispersed into SiC/C suspension by ball-milling and ultrasonic dispersion. By chemical etching, the whisker displays the original burl profile on the polished surface of the composite. The raise of whisker fraction leads to an increase of porosity of the green body; and thus a decrease of density of the sintered body. For the specimen with 25 wt.% whisker, the rapid reaction of carbon with excess molten silicon leads to the missing of burl profile on the whisker surface. It is speculated that β-SiC on the whisker surface dissolved in the molten silicon during liquid silicon infiltration.

Morphology of SiC Whisker in Whisker Reinforced Reaction Bonded SiC Composite

SiC whisker was introduced into reaction bonded silicon carbide to produce high performances composite by slip casting and reaction sintering. This study aimed at morphology of SiC whisker in the reaction bonded silicon carbide ceramics. The whisker was homogeneously dispersed into SiC/C suspension by ball-milling and ultrasonic dispersion. By chemical etching, the whisker displays the original burl profile on the polished surface of the composite. The raise of whisker fraction leads to an increase of porosity of the green body; and thus a decrease of density of the sintered body. For the specimen with 25 wt.% whisker, the rapid reaction of carbon with excess molten silicon leads to the missing of burl profile on the whisker surface. It is speculated that β-SiC on the whisker surface dissolved in the molten silicon during liquid silicon infiltration.