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1.
《Ceramics International》2017,43(9):6786-6790
As-received and pre-coated SiC whiskers (SiCw)/SiC ceramics were prepared by phenolic resin molding and reaction sintering at 1650 °C. The influence of SiCw on the mechanical behaviors and morphology of the toughened reaction-bonded silicon carbide (RBSC) ceramics was evaluated. The fracture toughness of the composites reinforced with pre-coated SiCw reached a peak value of 5.6 MPa m1/2 at 15 wt% whiskers, which is higher than that of the RBSC with as-received SiCw (fracture toughness of 3.4 MPa m1/2). The surface of the whiskers was pre-coated with phenolic resin, which could form a SiC coating in situ after carbonization and reactive infiltration sintering. The coating not only protected the SiC whiskers from degradation but also provided moderate interfacial bonding, which is beneficial for whisker pull-out, whisker bridging and crack deflection.  相似文献   

2.
《Ceramics International》2023,49(1):392-402
Silicon carbide ceramic matrix composites are widely used in aerospace field due to their advantages of high temperature resistance, high strength and corrosion resistance. However, its application is greatly limited because of the difficulty in preparing complex shape structures by traditional machining methods. Here, a new strategy for preparing SiCw/SiC complex structure by combining direct ink writing with reaction bonding is proposed. A water-based slurry consisting of silicon carbide, carbon powder and silicon carbide whisker was developed. The influence laws of C content and SiCw content in slurry on sintering properties of direct-written samples were studied. The reaction bonding mechanism and whisker reinforcing and toughening mechanism were analyzed by means of microstructure and phase composition. The results show that the slurry exhibits shear thinning behavior with stress yield point, and its flow behavior and plasticity meet the requirements of direct writing. When the carbon content is 6.4 wt%, the maximum flexural strength is 239.3 MPa. When 15 wt% SiCw was added, the flexural strength of the composite reached 301.6 MPa, and when 20 wt% SiCw was added, the fracture toughness of the composite reached 4.02 MPa m1/2, which was increased by 26% and 18% compared with single-phase SiC, respectively. The reinforcing and toughening mechanisms of the whiskers mainly include whisker pullout, crack deflection and whisker bridging. After direct ink writing and reaction bonded, the whole process shows good near net forming ability. 3D printed SiCw/SiC composites have great application prospects in aerospace field.  相似文献   

3.
《Ceramics International》2020,46(7):9303-9310
The employment of coating technique on the silicon carbide fibers plays a pivotal role in preparing SiC fiber-reinforced SiC composites (SiCf/SiC) toward electromagnetic wave absorption applications. In this work, SiC nanowires (SiCNWs) are successfully deposited onto the pyrolytic carbon (PyC) coated SiC fibers by an electrophoretic deposition method, and subsequently densified by chemical vapor infiltration to obtain SiCNWs/PyC-SiCf/SiC composites. The results reveal that the introduction of SiCNWs could markedly enhance the microwave absorption properties of PyC-SiCf/SiC composites. Owing to the increasing of SiCNWs loading, the minimum reflection loss of composites raises up to −58.5 dB in the SiCNWs/PyC-SiCf/SiC composites with an effective absorption bandwidth (reflection loss ≤ −10 dB) of 6.13 GHz. The remarkable enhancement of electromagnetic wave absorption performances is mainly attributed to the improved dielectric loss ability, impedance matching and multiple reflections. This work provides a novel strategy in preparing SiCf/SiC composites with excellent electromagnetic wave absorption properties.  相似文献   

4.
The high sintering temperature would have a great tendency to damage the morphology and thus properties of the silicon carbide whisker (SiCw) in high entropy carbide-silicon carbide whisker (HEC-SiCw) composites, which, in turn, would impact the effectiveness of the operative toughening mechanisms. The objective of this study was to achieve full contributions to the toughening effects of SiCw by preparing (Ti, Zr, Nb, Ta, Mo)C-SiCw composites at low temperature (1600 ℃) using cobalt as additives. Results showed that the fracture toughness of the (Ti, Zr, Nb, Ta, Mo)C bulk reinforced with 20 vol% SiCw and 5 vol% Co was 7.2 MPa?m1/2, which was much higher than that of the (Ti, Zr, Nb, Ta, Mo)C bulk only sintered with 5 vol% Co (3.4 MPa?m1/2). Meanwhile, it was also higher than that of the reported HEC-20 vol% SiCw composite sintered at 2000 ℃ (4.3 MPa?m1/2). For the fracture toughness of HEC-SiCw composites, it was significantly increased by the introduction of damage-free SiCw.  相似文献   

5.
《Ceramics International》2020,46(5):5773-5778
In this research work, the effects of silicon carbide (SiC) as the most important reinforcement phase on the densification percentage and mechanical characteristics of zirconium diboride (ZrB2)-matrix composites were studied. In this way, a monolithic ZrB2 ceramic (as the baseline) and three ZrB2 matrix specimens each of which contains 25 vol% SiC as reinforcement in various morphologies (SiC particulates, SiC whiskers, and a mixture of SiC particulates/SiC whiskers), have been processed through spark plasma sintering (SPS) technology. The sintering parameters were 1900 °C as sintering temperature, 7 min as the dwell time, and 40 MPa as external pressure in vacuum conditions. After spark plasma sintering, a relative density of ~96% was obtained (using the Archimedes principles and mixture rule for evaluation of relative density) for the unreinforced ZrB2 specimen, but the porosity of composites containing SiC approached zero. Also, the assessment of sintered materials mechanical properties has shown that the existence of silicon carbide in ZrB2 matrix ceramics results in fracture toughness and microhardness improvement, compared to those measured for the monolithic one. The simultaneous addition of silicon carbide particulates (SiCp) and whiskers (SiCw) showed a synergistic effect on the enhancement of mechanical performance of ZrB2-based composites.  相似文献   

6.
《Ceramics International》2019,45(16):19808-19821
Silicon carbide whiskers (SiCw) in TiC had impressive impacts on the properties and made it possible for special applications which generally would not be conceivable with TiC alone. In the present work, SiCw reinforced TiC based composites were prepared by spark plasma sintering (SPS) technique, at the temperature of 1900 °C under the pressure of 40 MPa for sintering time of 7 min. To test out the effects of different amount of SiC whisker (0, 10, 20 and 30 vol%) on the characteristics of TiC, the sintered samples were investigated about sinterability and physical-mechanical properties. Microstructure observations and density measurements confirmed that the composites were dense with uniformly distributed reinforcement, and the specimen doped with higher than 10 vol% SiCw could attain higher relative density (>100%) than pure TiC and TiC–10 vol% SiCw. Also, the highest values for hardness (29.04 GPa) and thermal conductivity (39.2 W/mK) were achieved in specimen containing 30 vol% SiCw, whereas the optimum bending strength (644 MPa) was recorded in material containing 20 vol% SiCw. It seems that one of the reasons which contributes to this trend of properties variation is the generation of near-stoichiometric TiCx phase and new Ti3SiC2 compound.  相似文献   

7.
Silicon carbide whisker (SiCw) toughened B4C composites have been prepared by pressureless infiltration of B4C–SiCw–C preforms with molten silicon under vacuum at 1500 °C. The effect of SiCw addition on bulk density, hardness, bending strength, fracture toughness and microstructure of SiCw/B4C composites is discussed. It is revealed that the addition of SiCw improves the fracture toughness of B4C ceramic, but reduces its bending strength at the same time. The maximum fracture toughness for SiCw/B4C composite with 24 wt% SiCw addition is 4.88 MPa m1/2, which is about 9% higher than that of the one without SiCw, but at the same time, the bending strength reduces to the minimum value 243 MPa, reduced by 25%. XRD analysis shows that the phase composition of reaction bonded SiCw/B4C composites is B4C, SiC, Si, and B12 (C, Si, B)3, with no residual C. And the main toughening mechanism of SiCw is whisker pulling up.  相似文献   

8.
《Ceramics International》2020,46(11):18813-18825
This investigation intended to assess the influence of SiC morphology on the sinterability and physical-mechanical features of TiB2-SiC composites. For this aim, different volume percentages of SiC particles and SiC whiskers were introduced to TiB2 samples hot-pressed at 1950 °C for 2 h under an external pressure of 25 MPa. The characterization of as-sintered specimens was carried out using X-ray diffraction, optical microscopy, and scanning electron microscopy. The relative density studies revealed that SiCw had a more significant impact on the sinterability of TiB2-based composites. The XRD investigation confirmed the production of an in-situ TiC phase during the hot-pressing; however, some peaks related to the graphitized carbon also appeared in the patterns of SiCw-doped ceramics. The addition of 25 vol% SiCp halved the average grain size of TiB2 while introducing the same content of SiCw decreased this value by just around 20%. Finally, the highest Vickers hardness and fracture toughness were obtained for the sample reinforced with 25 vol% SiCw, standing at 29.3 GPa and 6.1 MPa m1/2, respectively.  相似文献   

9.
《Ceramics International》2023,49(20):32750-32757
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.  相似文献   

10.
Dense polycrystalline cBN (PcBN)–SiCw composites were fabricated by a two-step method: First, SiO2 was coated on the surface of cubic boron nitride (cBN) particles by the sol-gel method. Then, silicon carbide whisker (SiCw)- coated cBN powder was prepared by carbon thermal reaction between SiO2 and carbon powders at 1500°C for 2 hour. Then, cBN–SiCw complex powders were sintered by high-pressure and high-temperature sintering technology using Al, B, and C as sintering additives. The phase compositions and microstructures of cBN–SiCw composites were investigated by X-ray diffraction and scanning electron microscopy, respectively. It was found that the SiCw and Al3BC3 had been fabricated by in situ reaction, which cannot only promote densification but also improve mechanical properties. The relative density of PcBN composites increased from 96.3% to 99.4% with increasing SiCw contents from 5 to 20 wt%. Meanwhile, the Vickers hardness, fracture toughness and flexural strength of as-obtained composites exhibited a similar trend as that of relative density. The composite contained 20 wt% of SiCw exhibited the highest Vickers hardness and fracture toughness of 42.7 ± 1.9 GPa and 6.52 ± 0.21 MPa•m1/2, respectively. At the same time, the flexural strength reached 406 ± 21 MPa.  相似文献   

11.
《Ceramics International》2022,48(7):9483-9494
In this work, quasi-isotropic chopped carbon fiber-reinforced pyrolytic carbon and silicon carbide matrix (Cf/C–SiC) composites and chopped silicon carbide fiber-reinforced silicon carbide matrix (SiCf/SiC) composites were prepared via novel nondamaging method, namely airlaid process combined with chemical vapor infiltration. Both composites exhibit random fiber distribution and homogeneous pore size. Young's modulus of highly textured pyrolytic carbon (PyC) matrix is 23.01 ± 1.43 GPa, and that of SiC matrix composed of columnar crystals is 305.8 ± 9.49 GPa in Cf/C–SiC composites. Tensile strength and interlaminar shear strength of Cf/C–SiC composites are 52.56 ± 4.81 and 98.16 ± 24.62 MPa, respectively, which are both higher than those of SiCf/SiC composites because of appropriate interfacial shear strength and introduction of low-modulus and highly textured PyC matrix. Excellent mechanical properties of Cf/C–SiC composites, particularly regarding interlaminar shear strength, are due to their quasi-isotropic structure, interfacial debonding, interfacial sliding, and crack deflection. In addition to the occurrence of crack deflection at the fiber/matrix interface, crack deflection in Cf/C–SiC composites takes also place at the interface between PyC–SiC composite matrix and the interlamination of multilayered PyC matrix. Outstanding mechanical properties of as-prepared Cf/C–SiC composites render them potential candidates for application as thermal structure materials under complex stress conditions.  相似文献   

12.
《Ceramics International》2020,46(11):18965-18969
Silicon carbide ceramics were prepared by liquid-phase assisted oscillatory pressure sintering (OPS) with graphene and in-situ synthesized SiC whisker as the reinforcements. The effects of sintering temperature on the densification, morphology and mechanical performances of the SiCp-SiCw-graphene ceramics were investigated. In the temperature range from 1700 to 1800 °C, the densification rate of SiCp-SiCw-graphene ceramics was accelerated, ascribing to the reduction in viscosity of the glassy phase. At 1800 °C, the flexural strength and fracture toughness of the OPS ceramics corresponded to 697 MPa and 5.8 MPa m1/2, respectively, which were higher than that of the hot-pressed ceramics under the same temperature conditions. Multiphase toughening mechanisms, such as whisker bridging and pullout, graphene bridging and delamination, were considered as the primary mechanisms. This work demonstrates an effective strategy to prepare silicon carbide ceramics at low sintering temperature.  相似文献   

13.
Reaction‐bonded silicon carbide (RBSC) was prepared by ceramic injection molding (CIM) technique with feedstocks containing silicon carbide (SiC), a wax‐based organic system and different amounts of carbon black. As a critical effect of the reaction sintering process, carbon was introduced from the carbon black and the decomposition product of the organic polymers, respectively. This study described the influence of carbon content on the mixing and injection process firstly and then emphasized the debinding process since it played a large role in the process of the pyrolysis of organic. Results indicated that the preferable thermal debinding was performed in N2 and the optimal performance was obtained for RBSC with 7 wt.% of carbon black, with the density of 2.98 g/cm3, apparent porosity of 0.24%, bending strength of 301.59 MPa and fracture toughness of 4.18 MPa·m1/2.  相似文献   

14.
Alternating pyrolytic carbon/boron nitride (PyC/BN)n multilayer coatings were applied to the KD–II silicon carbide (SiC) fibres by chemical vapour deposition technique to fabricate continuous SiC fibre-reinforced SiC matrix (SiCf/SiC) composites with improved flexural strength and fracture toughness. Three-dimensional SiCf/SiC composites with different interfaces were fabricated by polymer infiltration and pyrolysis process. The microstructure of the coating was characterised by scanning electron microscopy, X–photoelectron spectroscopy and transmission electron microscopy. The interfacial shear strength was determined by the single-fibre push-out test. Single-edge notched beam (SENB) test and three-point bending test were used to evaluate the influence of multilayer interfaces on the mechanical properties of SiCf/SiC composites. The results indicated that the (PyC/BN)n multilayer interface led to optimum flexural strength and fracture toughness of 566.0?MPa and 21.5?MPa?m1/2, respectively, thus the fracture toughness of the composites was significantly improved.  相似文献   

15.
This study aimed to investigate the toughening effects of SiC nanowires (SiCnw) and SiC whiskers (SiCw) on high-entropy carbide based composites prepared at different temperatures (1600°C and 2000°C). At low temperature (1600°C), SiCnw and SiCw maintain their original morphology and properties, and exhibit the good toughening effects. The SiCnw with larger aspect ratio and more curly wires exhibit a much stronger toughening effect on the (Ti0.2Zr0.2Nb0.2Ta0.2Mo0.2)C0.8 composites reinforced with 15 vol.% SiCnw, which shows the highest value of fracture toughness about 6.7 MPa∙m1/2. However, at high sintering temperature (2000°C), SiCnw and SiCw are prone to thermal-induced damages, which significantly reduces their mechanical properties, and thus, toughening effects on (Ti0.2Zr0.2Nb0.2Ta0.2Mo0.2)C0.8 composites. The addition of SiCw, which have better thermal stability at 2000°C, results in the (Ti0.2Zr0.2Nb0.2Ta0.2Mo0.2)C0.8–15 vol.% SiCw composite exhibiting relatively better fracture toughness, about 3.7 MPa∙m1/2. Based on the results of the current study, the critical influence of SiCnw and SiCw on the toughening of (Ti0.2Zr0.2Nb0.2Ta0.2Mo0.2)C0.8 composites is highly dependent on their high-temperature thermal stability.  相似文献   

16.
The zirconia toughened alumina (ZTA) composites have been widely used as an engineering material in many application areas due to their remarkable mechanical properties. However, the fracture toughness of ZTA does not generally meet the requirements of aerospace, machinery and other fields. In this study, the SiC whiskers (SiCw) have been incorporated in the ZTA composites to improve the fracture toughness. The SiCw employed in this study mainly consist of the β phase, with a small fraction of the α phase. The effect of the SiCw content and sintering temperature on the microstructure and mechanical properties of the SiCw-ZTA (ZASw) composites has been systematically studied. The incorporation of SiCw is noted to reduce the density of the ZASw composites. On enhancing the SiCw content, the Vickers hardness and fracture toughness of the composites initially decrease, followed by an increase. However, the flexural strength of the composites increases with the SiCw content. At a SiCw content of 10.0 vol %, the strength, hardness and toughness are observed to reach the maximum values. On enhancing the sintering temperature, the strength and hardness of the composites are observed to remain nearly constant, while the toughness of the composites is increased.  相似文献   

17.
To tailor the fiber–matrix interface of SiC nanowires-reinforced SiC (SiCnw/SiC) ceramic matrix composites (CMCs) for improved mechanical properties, SiC nanowires were coated with BN and pyrolytic carbon (PyC) compound coatings prepared by the dip-coating process in boric acid and urea solution and the pyrolysis of phenolic resin. SiCnw/SiC CMC with PyC/BN interfaces were fabricated by reactive melt infiltration (RMI) at 1680°C for 1 h. The influences of phenolic resin content on the microstructure and mechanical properties of the CMC were investigated. The results showed that the flexural strength and fracture toughness reach the maximum values of 294 MPa and 4.74 MPa m1/2 as the phenolic resin content was 16 and 12 wt%, respectively. The displacement–load curve of the sample exhibited a gradient drop with increasing phenolic resin content up to 12 wt%. The results demonstrated that the PyC/BN compound coatings could play the role of protecting the SiCnw from degradation as well as improving the more moderate interfacial bonding strengths during the RMI.  相似文献   

18.
Effects of SiC whiskers (SiCw) on the mechanical properties of composites largely depend on their thermal stability at high temperature. In this study, pure SiCw and Ti3SiC2 coated SiCw were thermal treated at 1600–1800°C for 1 h. Their phase assemblage, morphology, and structural evolution were investigated. Oxygen partial pressures in the graphite furnace resulted in the breakdown of SiCw into particles at 1600°C, and the degradation became more pronounced with temperature increasing. The thermal stability of SiC whiskers at 1600–1700°C was significantly improved by a thin Ti3SiC2 coating on them, as both thermodynamic calculations and experimental observations suggest Ti3SiC2 coating could be preferentially oxidized/decomposed, prior to the active oxidation of SiC. At 1800°C, the protective role of the coating on the whiskers became weakened. SiC was converted into gaseous SiO and CO, with the remaining of interconnected TiC micro-rods and amorphous carbon.  相似文献   

19.
Laminated Si3N4/SiCw ceramics were successfully prepared by tape casting and hot-pressing. Its mechanical properties were measured and the impact resistance was discussed. The toughness of the laminated Si3N4/SiCw ceramics was 13.5 MPa m1/2, which was almost 1.6 times that of Si3N4/SiCw composite ceramics, namely 8.5 MPa m1/2. Moreover, the indentation strength of laminated Si3N4/SiCw ceramics was not sensitive to increasing indentation loads and exhibited a rising R-curve behaviour, indicating that the laminated Si3N4/SiCw ceramics had excellent impact resistance. The improved toughness and impact resistance of laminated Si3N4/SiCw ceramics was attributed to the residual stress caused by a thermal expansion coefficient mismatch between the different layers, resulting in crack deflection and bridging of SiC whiskers in the interface layer, thus consuming a large amount of fracture work.  相似文献   

20.
Reaction‐bonded silicon carbide ceramics fabricated from tape casting and Si infiltration have been reported in previous studies. To reduce the residual Si content in the sintered bodies, impregnation of phenol–formaldehyde resin (PF) into the porous green preforms before Si infiltration was proposed and studied in this work. The impregnation of PF solution not only helped to reduce the porosity and increase the carbon content of the green preforms, but also improved their strength. As a result, the flexural strength of the RBSC increased a lot and reached 856 ± 161MPa, whereas the residual Si content was reduced to 10 vol%.  相似文献   

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