Sintering Of SiC Research Articles

Characterization and Properties of Silicon Carbide Reinforced Ni-10Co-5Cr (Superalloy) Matrix Composite Produced Via Powder Metallurgy Route

In this investigation, Ni-Co-Cr-SiC composites with various weight percentages were manufactured via powder metallurgy (PM) route. The compositions of the composites are Ni-10%Co-5%Cr, Ni-10% Co-5%Cr-4%SiC, Ni-10%Co-5%Cr-8%SiC and Ni-10%Co-5%Cr-12%SiC. The powders were mixed using planetary ball mill for a period of 10 h. The ball milled powders were subjected to X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) analysis. By utilizing 150 kN hydraulic press with appropriate punch and die the ball milled powders were compacted as a cylindrical billets. The green compacts were sintered in a tubular furnace at two different temperatures 1000 °C and 1200 °C for3 h. The characterization examination namely XRD, SEM and Energy Dispersive Analysis (EDAX) was made on the sintered samples. Unreinforced Ni-Co-Cr exhibits higher sinterability at both sintering temperature. The sintering temperature and reinforcement weight percentage effect on the mechanical properties and corrosion behavior of the composites were examined. From these investigations, the mechanical properties and corrosion resistance of the composites were enhanced while increasing the sintering temperature and SiC weight percentage in the Ni-Co-Cr super alloy matrix.

Effect of sintering techniques on microstructural, mechanical and tribological properties of Al-SiC composites

In this paper, the effects of sintering techniques (conventional, CS and electric resistance, ERS) and SiC content (1, 3 and 5 wt. %) on the microstructural, mechanical and tribological properties were investigated. Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were performed for microstructural investigation. Density, porosity and hardness were evaluated at different weight fractions of SiC for comparative study. Tribological behaviour was evaluated in terms of wear loss and coefficient of friction (COF). Worn-out surfaces and formed debris were also studied using SEM for understanding the wear mechanism. Results indicated that addition of SiC improved the hardness, wear resistance and COF. With addition of 5 wt. % SiC the hardness improved by 32 % for CS and 30% for ERS, wear resistance improved by 37 % for CS and 40% for ERS while COF improved by 3 % for CS (3 wt.% SiC) and 6 % for ERS (5 wt.% SiC) compared to neat Al. ERS processed composites resulted in better densification, improved hardness (12-14%) and tribological behaviour (wear resistance 36-39 % and COF 7-15 %) for 1-5 wt. % SiC compared to CS processed ones. Abrasion, adhesion and delamination were the controlling wear mechanism for Al-SiC composites with lesser adhesion wear in ERS composites.

Preparation of SiC@Al2O3–Y2O3 core-shell nanoparticles by a slow precipitation method for dense SiC sintering

High sintering temperatures and high pressures are often needed for the densification of SiC. The sintering of SiC can be facilitated by adding Al2O3–Y2O3 oxides as the sintering additives. In the present study, the SiC@Al2O3–Y2O3 composite nanoparticles with a core-shell structure were designed and prepared using a slow co-precipitation method in the presence of urea. It was found that by slowing down the hydrolysis rate of the metal ions, Al(OH)3 and Y(OH)3 could be co-precipitated and uniformly coated on the surface of the SiC nanoparticles by a heterogeneous nucleation mechanism. After subsequent heat treatment, SiC@Al2O3–Y2O3 nanoparticles with amorphous Al2O3–Y2O3 layers of 2–3 nm were obtained. SiC ceramics with different oxides aids were prepared by sintering the core-shell nanoparticles at 1800–1900 °C under a pressure of 30 MPa. For SiC with higher additives of 20 wt%, evident volatilization of the oxide aids occurred at high temperatures with the segregation of the oxides. For the sample sintered at 1800 °C, dense SiC ceramics with uniform sintering aids distribution were obtained with the Al2O3–Y2O3 content as low as 5 wt% and a surface Vickers hardness of 31.5 GPa was obtained.

SiC- and Ti3SiC2-Based Ceramics Synthesis by Spark Plasma Sintering of Preceramic Paper

This paper is devoted to proposing a new approach to the synthesis of SiC- and Ti3SiC2-based ceramics by using of preceramic paper as a feedstock. A preceramic paper with SiC and Ti3SiC2 powder fillers were sintered by spark plasma sintering (SPS) method for holding time 10 minutes under pressure 20-100 MPa. The temperature for the sintering of SiC- and Ti3SiC2-filled paper was 2073-2373 K and 1373-1473 K respectively. The influence of sintering parameters on the materials microstructure was analyzed by scanning electron microscopy. It was revealed that with an increase in pressure from 20 to 100 MPa, the microstructure of the materials becomes denser. It agrees with the results of measuring the density of the sintering materials by the hydrostatic weighting. The determination of Young`s modulus by the acoustic method demonstrates that with the increase of the applied pressure during SPS, Young’s modulus of the synthesized SiC- and Ti3SiC2-ceramics increase.

Reaction-bond composite synthesis of SiC-TiB2 by spark plasma sintering/field-assisted sintering technology (SPS/FAST)

High-density SiC-TiB2 composites were fabricated using the displacement reaction spark plasma sintering/field-assisted sintering technology (SPS/FAST) and SiC, B4C, TiC, and Si powders. The reaction process was performed in a narrow time frame compared hot pressing. The SiC-TiB2 composites were sintered with precursor SiC at various pressures to determine the effects of processing with SPS/FAST. The composites completed synthesis during SPS/FAST processing, which occurs more quickly than hot pressing. SEM, STEM, and Raman spectroscopy are used to show the conversion and microstructure. The composite of 53.6 wt.% SiC and 46.4 wt.% TiB2 has 99 % theoretical density, hardness of 26.4 GPa, and fracture toughness of 5.12 MPa m1/2.

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.

Processing of solid state sintered α-SiC ceramics with carbon-black addition

The efficient removal of surface silica layer from SiC particles by the addition of carbon is required for solid state sintering (SSS) of SiC ceramics. While wax-based organics are generally utilized as carbon source in many commercial SSS-SiC ceramics, carbon black powders with high specific surface area (SSA) are potential alternatives as carbon source, which can be dispersed in ceramic slurries directly without needing any additional pyrolysis reactions. In this study, carbon black powders were utilized as carbon source for sintering of SiC. The effect of particle size of carbon black powders on densification and microstructural development during pressureless and spark plasma sintering (SPS) were investigated. It was observed that while the density of the SiC samples increased with increasing SSA of carbon black powders, complete densification was not achieved for all samples in case of pressureless sintering due to the flaws originated by carbon black segregation on granule surfaces. SPS was found an effective sintering method for the elimination of such flaws and SiC ceramics were sintered to 100% of theoretical density independent from the particle size of the carbon black powders in this sintering technique.

Synthesis of SiC@Al2O3 core–shell nanoparticles for dense SiC sintering

Owing to the difficulty for dense SiC sintering, high sintering temperatures and pressures are usually needed. Lowering the sintering temperature by adding Al2O3 as a sintering additive has previously been shown to be beneficial. However, traditional addition methods limit the effect of the Al2O3 owing to inhomogeneous mixing at the nanoscale. A SiC@Al2O3 composite nanoparticle with a core–shell structure is designed and prepared using the slow co-precipitation method. The differences between this method and the traditional mechanical ball milling method are interpreted by different experimental parameters, such as temperature, pressure, amount of additive, and mixing type. It is found that the method of slow co-precipitation enables homogeneous mixing of Al2O3 and SiC at a smaller scale, and makes the sintered SiC much denser and more homogeneous, when compared with the traditional method. The parameters of sintering at 1900°C and 30MPa for 30min are recommended. The conclusions here are also beneficial for the sintering research of other ceramic materials.

The effect of aluminum additive on pressureless sintering of SiC

This study was carried out to investigate the effect of Al additive amount on the microstructure development and room temperature mechanical properties of pressureless sintered silicon carbide. Different amounts of Al containing of 1, 2.5, 5, 10, and 15 wt% were added to the base material and pressureless sintering was conducted at 1950 °C for 1 h under argon atmosphere. The formation of the Al4SiC4 phase during conventional sintering was confirmed by X-ray diffraction (XRD) analysis. Microstructure, crystal phases, and density evolution were studied and correlated to Al additions and pre-sintered proceedings. The obtained results show that the addition of Al not only improves sinterability at lower temperature, but also enhances densification and hardness of SiC samples (3.05 g/cm3 and 26.9 GPa respectively).

Enhancing toughness and strength of SiC ceramics with reduced graphene oxide by HP sintering

In this paper, the silicon carbide-reduced graphene oxide (SiC/rGO) composites with different content of rGO are investigated. The hot pressing (HP) at 2100 °C for 60 min under a uniaxial pressure of 40 M Pa resulted in a near fully-dense SiC/rGO composite. In addition, the influence of graphene reinforcement on the sintering process, microstructure, and mechanical properties (fracture toughness, bending strength, and Vickers hardness) of SiC/rGO composites is discussed. The fracture toughness of SiC/rGO composites (7.9MPam1/2) was strongly enhanced by incorporating rGO into the SiC matrix, which was 97% higher than the solid-state sintering SiC ceramics (SSiC) by HP. Meanwhile, the bending strength of the composites reached 625 M Pa, which was 17.3% higher than the reference materials (SSiC). The microstructure of the composites revealed that SiC grains were isolated by rGO platelets, which lead to the toughening of the composite through rGO pull out/debonding and crack bridging mechanisms.

Controllable preparation of SiC coating protecting carbon fiber from oxidation damage during sintering process and SiC coated carbon fiber reinforced hydroxyapatite composites

As a kind of ideal artificial bone materials, poor mechanical properties especially brittleness of pure hydroxyapatite (HA) have limited its clinical application. In order to achieve pressureless sintering of carbon fiber (CF) reinforced HA bioceramics, SiC coating was successfully prepared on CF surface by low pressure chemical vapor deposition (LPCVD). The structure, morphology, and thickness of the SiC coating are controllable. The SiC coated CF (SiC-CF) reinforced HA composites (SiC-CF/HA) were prepared via pressureless sintering at 1373 K for 20 min. The bending strength of the SiC-CF/HA composite reaches its maximum achievable value of 28.4 MPa, when 0.5 wt% of SiC-CF was added. It is almost three times that of pure HA sintered under an identical condition. The corresponding fracture toughness is as high as 1.28 MPa·m1/2, which are 26.6% and 19.5% increase over those of HA and CF/HA composites, respectively. The enhancements of the bending strength and fracture toughness are mainly due to enhancing and toughening mechanism (crack-bridging and pull-out of SiC-CF). In practice, SiC coating acts as an oxygen diffusion barrier to prevent the oxidative damage of CF caused by dehydroxylation of HA during pressureless sintering. Furthermore, the SiC coating has the ability to form a transitional SiO2 layer in an oxidizing atmosphere which fills the cracks of the coating, enhances the interfacial compatibility, and lessens the interfacial stress. The study provides additional insights into the feasibility of SiC-CF/HA composites as load-bearing implant materials in clinical applications.

Thermal shock resistance of pressureless sintered SiC/AlN ceramic composites

This paper conducts for the first time, a study of thermal shock resistance properties of different pressureless sintered SiC/AlN ceramic composites. SiC/AlN composites with different AlN content (0–40 wt%) were obtained by pressureless sintering of SiC and AlN powders at temperature of 2080 °C/2 h in Ar/vacuum atmosphere with using 2.5% yttria and alumina as sintering aids. The different ceramic composites are subjected to 20 thermal shock/water quenching cycles at temperature of 700 °C. Mechanical strength and microstructure investigation before and after thermal shock exposure were used to evaluate thermal shock properties and durability of the different composites. It was found that, the investigated carbide/nitride ceramics gave high thermal shock resistance without any cracking or spalling with retention of about 70% of its original strength. Results suggest that, SiC/AlN composites are strong candidate in severe thermal shock resistance environments.

Processing and properties of cordierite-silica bonded porous SiC ceramics

Abstract Cordierite-silica bonded porous SiC ceramics were fabricated by infiltrating a porous powder compact of SiC with cordierite sol followed by sintering at 1300–1400 °C in air. The porosity, average pore diameter and flexural strength of the ceramics varied 30–36 vol%, ~ 4–22 µm and ~ 13–38 MPa respectively with variation of sintering temperature and SiC particle sizes. In the final ceramics SiC particles were bonded by the oxidation-derived SiO 2 and sol-gel derived cordierite. The corrosion behaviour of sintered SiC ceramics was studied in acidic and alkaline medium. The porous SiC ceramics were observed to exhibit better corrosion resistance in acid solution.

Effects of in situ synthesized mullite whisker on mechanical properties of Al2O3–SiC composite by microwave sintering

In situ synthesis of mullite whisker was introduced to Al2O3–SiC composite by microwave sintering. The effects of sintering parameters (sintering temperature, holding time and SiC particle size) on thermal shock resistance of Al2O3–SiC composite were also studied in this paper. Original SiC particles coated with SiO2 by a sol–gel method were reacted with Al2O3 particles, resulting in the in situ growth of mullite. The phase composition was identified by x-ray diffraction (XRD). The bridging of mullite whisker between Al2O3 and SiC particles was observed by scanning electron microscopy (SEM) analysis. The thermal shock resistance of samples was investigated through the combination of water quenching and three-point bending methods. The results show that the thermal shock resistance of Al2O3–SiC composite with mullite whisker reinforced remarkably, indicating better mechanical properties than the Al2O3–SiC composite without mullite whisker. Finally, the optimum process parameters (the sintering temperature of 1500 °C, the holding time of 30 min, and the SiC particle size of 5 µm) for toughening Al2O3–SiC composite by in situ synthesized mullite whisker were obtained.

Influence of the SiC content and sintering temperature on the microstructure, mechanical properties and friction behaviour of sintered self-lubricating composites

This work reports the development of a new, low-friction coefficient combined with high mechanical strength and scuffing resistance of self-lubricating composite produced by powder injection moulding process and the recently introduced plasma-assisted debinding and sintering process. We present and discuss the effect of sintering temperature and SiC content on the microstructure, mechanical and friction properties. Three different temperatures (1100,1150, 1200°C) and six different SiC contents (0–5%) were analysed. SiC content had a paramount role on the microstructure, mechanical and friction behaviour. Sintering temperature had almost no effect on the friction coefficient. However, the sintering temperature strongly influences scuffing resistance. Raman spectra obtained in the central region of the wear scar indicate the presence of turbostratic two-dimensional graphite. The misorientation between graphene planes and the increase in interlamellae distance may induce a low interaction between these atomic planes and are, probably, the origin of the low-friction coefficient.

Liquid-phase assisted flash sintering of SiC from powder mixtures prepared by aqueous colloidal processing

The effects were investigated of the starting particle size (i.e., nanometer or submicrometer powders), content of Y3Al5O12 additives (YAG; in the range 5–20wt.%), and difference of size scales between the two particle types on the liquid-phase assisted flash sintering of SiC from powder mixtures prepared by aqueous colloidal processing. It was found that flash sintering benefits from the refinement of the particles size, the increase in additive content, and the smaller size scale of the particulate additive. It was also found that under the present flash sintering conditions (i.e., 900°C furnace temperature, 13A current, and 50s in flash state) the resulting ceramics are, despite the formation of liquid phase, porous to a greater or lesser extent, and exhibit decreasing porosity gradients from their surface to the centre. These observations are rationalized to extract guidelines for powder batch design contributing to the pressureless ultrafast sintering of non-oxide advanced ceramics.

Tribological properties of SiC-based MCD films synthesized using different carbon sources when sliding against Si3N4

Micro-crystalline diamond (MCD) films are deposited on reactive sintering SiC substrates by the bias enhanced hot filament chemical vapor deposition (BE-HFCVD) method, respectively using the methane, acetone, methanol and ethanol as the carbon source. Two sets of standard tribotests are conducted, adopting Si3N4 balls as the counterpart balls, respectively with the purpose of clarifying differences among tribological properties of different MCD films, and studying detailed effects of the carbon source C, normal load Fn and sliding velocity v based on orthogonal analyses. It is clarified that the methane-MCD film presents the lowest growth rate, the highest film quality, the highest hardness and the best adhesion, in consequence, it also performs the best tribological properties, including the lowest coefficient of friction (COF) and wear rate Id, while the opposite is the methanol-MCD film. Under a normal load Fn of 7N and at a sliding velocity v of 0.4183m/s, for the methane-MCD film, the maximum COF (MCOF) is 0.524, the average COF during the relatively steady-state regime (ACOF) is 0.144, and the Id is about 1.016×10−7mm3/N m; and for the methanol-MCD film, the MCOF is 0.667, the ACOF is 0.151, and the Id is 1.448×10−7mm3/N m. Moreover, the MCOF, ACOF, Id and the wear rate of the Si3N4 ball Ib will all increase with the Fn, while the v only has significant effect on the ACOF, which shows a monotone increasing trend with the v.

Preparation and Thermal Properties of Pressureless Sintered AIN/SiC Composites

AlN/SiC composites with 5 wt.% Y2O3 addition were fabricated by pressureless sintering at 1700-1950 oC. The influences of sintering temperature and SiC content on the relative density, mechanical property and thermal conductivity were studied. With sintering temperature increasing from 1700 oC to 1750 oC, the relative density increased significantly to about 98.0%, without evident changes from 1750 oC to 1900 oC, and then decreased slightly at 1950 oC. As SiC content increased, the flexural strength of composites sintered at 1750 oC increased firstly, and then decreased, obtaining a maximum flexural strength of 337 MPa at 20 wt.% SiC content. Meanwhile, the thermal conductivity decreased from 60 W/(m∙K) to 40 W/(m∙K) with SiC content increasing from 0 wt.% to 30 wt.%. Moreover, in the sintering temperature range from 1750 oC to 1950 oC, the thermal conductivity increased from 45 W/(m∙K) to 55 W/(m∙K) for AlN-10 wt.% SiC composites, but decreased from 40 W/(m∙K) to 36 W/(m∙K) for AlN-30 wt.% SiC composites.

Mechanical and thermal properties of low temperature sintered silicon carbide using a preceramic polymer as binder

Silicon carbide is used for a variety of applications, however, sintering still remains a challenge due to the high temperature and pressure required as well as the need for sintering aids. The use of preceramic polymers as binder is a promising technique for pressureless low-temperature sintering of SiC without sintering aids. However, the mechanical and thermophysical properties as well as the microstructure of bodies sintered through this technique has not been extensively documented. One of the main polymers which has gained attention in the past few years as a SiC preceramic is allylhydridopolycarbosilane (AHPCS). Here, using AHPCS as binder, silicon carbide pellets were sintered at temperatures as low as 930 °C, and the microstructural, mechanical, and thermophysical property characterization is presented. Compared to conventionally sintered SiC, the material shows similar fracture toughness, lower hardness, strength, and thermal conductivity. The observed properties are explained as a result of residual porosity combined with amorphous SiC at the grain boundaries.

The role of carbon and SiO2 in solid-state sintering of SiC

The role of carbon in reducing SiO2 during solid-state sintering of SiC was directly shown using a model experiment, where transmission electron microscopy was used to follow oxidation and reduction of the surface of SiC single crystals. These results corroborated the microstructural characterization of pressureless sintered polycrystalline SiC, undoped or doped with carbon (3wt.%) and boron (0.5wt.%). While samples doped with carbon and boron reached a density of 96% after 4h of sintering at 2100°C, undoped samples did not sinter, and the microstructure was characterized by particle coarsening and a film of SiO2. The lack of densification for undoped samples is explained by the low surface energy of SiO2 compared to the grain boundary energy of SiC, which reduces the driving force for densification.