Si/SiC ceramic composite and lnvar alloy were successfidly joined by vacuum brazing using Ti5OCu-W filler metals into which W was added to release the thermal stress of the brazed joint. Microstructures of the brazed ...Si/SiC ceramic composite and lnvar alloy were successfidly joined by vacuum brazing using Ti5OCu-W filler metals into which W was added to release the thermal stress of the brazed joint. Microstructures of the brazed joints were irwestigated by scanning electron micrascope （SEM） and energy dispersive spectrometer （EDS）. The mechanical properties of the brazed joints were measured by shearing tests. The results showed that the brazed joints were composed of Ti-Cu phase, W phase and Ti-Si phase. W had no effect on the wettability and mobility of the .filler metals. The growth of Ti2 Cu phase was restrained, and the reaction between ceramic composite and filler metals was weakened. The specimen, brazed at 970°C for 5 rain, had the maximum shear strength of 108 MPa at room temperature.展开更多
Three kinds of Mo-Ni-Si metallized coatings with various chemical compositions were deposited on SiC ceramic substrates by vacuum fusion sintering process, and the phase compositions of the coatings and their interfac...Three kinds of Mo-Ni-Si metallized coatings with various chemical compositions were deposited on SiC ceramic substrates by vacuum fusion sintering process, and the phase compositions of the coatings and their interface microstructures were analyzed. The wetting and spreading properties of molten Ag on the coated SiC ceramic substrates were investigated by the sessile drop technique, and the interfacial behavior of the Ag/coated SiC systems was analyzed. The results show that the coatings are mainly composed of Mo5Si3, MoSi2, Ni2Si, NiSi2 and MoNiSi. The tetragonal MoSi2 grains on the coating surface disappear gradually with the concentration of Mo increasing from 20 at% to 40 at%. The final contact angles of Ag/coated SiC systems at 1000 ℃ for holding 30 min are 45°, 79° and 85° for the coating compositions of Mo20-Ni32-Si48, Mo30-Ni28-Si42 and Mo40-Ni24-Si36, respectively. This result could be closely related to the interactions between the Ag drop and the microstructures of the three Mo-Ni-Si coatings. No obvious reaction layers are found at all the coating/substrate interfaces before and after the wetting tests.展开更多
Researching for interphase materials that can protect SiC fibers from oxygen and water vapor attacks has become one of the most important issues for the applications of SiC_f/SiC composites in high-temperature combust...Researching for interphase materials that can protect SiC fibers from oxygen and water vapor attacks has become one of the most important issues for the applications of SiC_f/SiC composites in high-temperature combustion environment. However, such kinds of interphase materials are not available yet. Herein,we report theoretically predicted properties of two promising interphase materials Y_5Si_3 C and Y_3Si_2C_2.Although crystallizing in different structures, they share the common features of layered structure,anisotropic chemical bonding, anisotropic electrical and mechanical properties, and low shear deformation resistance. The bulk moduli for Y_5Si_3C and Y_3Si_2C_2 are 78 and 93 GPa, respectively; while their shear moduli are 52 and 50GPa, respectively. The maximum to minimum Young's modulus ratios are1.44 for Y_5Si_3C and 3.27 for Y_3Si_2C_2. Based on the low shear deformation resistance and low Pugh's ratios(G/B = 0.666 forY_5Si_3C and 0.537 for Y_3Si_2C_2; G: shear modulus; B: bulk modulus), they are predicted as damage tolerant and soft ceramics with predicted Vickers hardness of 9.6 and 6.9 GPa, respectively.The cleavage plane and possible slip systems are(000 l) and(0001)[1120] and(1010)[0001] forY_5Si_3C,and those for Y_3Si_2C_2 are {h00} and(010)[101]. Since the oxidation products are water-vapor resistant Y2 Si2 O7, Y2 SiO5 and/or Y_2 O_3 upon oxidation, and the volume expansions are ca 140% and ca 26% for Y_5Si_3C and Y_3Si_2C_2, they are expected to seal the interfacial cracks in SiC_f/SiC composites. The unique combination of easy cleavage, low shear deformation resistance, volume expansions upon oxidation, and the resistance of the oxidation products to water vapor attack warrant them promising as interphase materials of SiC_f/SiC composites for water-vapor laden environment applications.展开更多
Silica-based ceramic cores have been widely used to fabricate aero-engine hollow blades due to their moderate high temperature mechanical properties and excellent leachability.In this study,silica-based ceramics with ...Silica-based ceramic cores have been widely used to fabricate aero-engine hollow blades due to their moderate high temperature mechanical properties and excellent leachability.In this study,silica-based ceramics with SiC fiber addition were prepared via stereolithography,and the influence of SiC fiber content on mechanical properties of the obtained silica-based ceramics was investigated.With the increase of SiC fiber content,linear shrinkage gradually decreased,while room temperature flexural strength and high temperature flexural strength first increased and then decreased.As SiC fiber content increased to 4.0 wt%,linear shrinkage was reduced to 0.62%resulting from the oxidation of SiC.Furthermore,room temperature flexural strength was improved from 11.79 MPa to 23.83 MPa and high temperature flexural strength was enhanced from 15.64 MPa to 34.62 MPa with 4.0 wt%SiC fiber addition due to the reinforcement of fibers and the enhancedβ-cristobalite content,which meets the need of ceramic cores.Therefore,it demonstrates the capability of fabricating high-performance and high-precision silica-based ceramic cores reinforced by SiC fibers via stereolithography for rapid manufacturing of hollow blades.展开更多
Silicon carbide (SiC) ceramics have excellent properties and widely used for high temperature applications. So far, joining techniques have been applied to fabricate large SiC ceramics with complicated shapes. In this...Silicon carbide (SiC) ceramics have excellent properties and widely used for high temperature applications. So far, joining techniques have been applied to fabricate large SiC ceramics with complicated shapes. In this work, the additive manufacturing (AM) technique was examined to fabricated SiC ceramics with complicated hollow structures using the Fused Deposition Modeling (FDM) type 3D-printer. To mold the hollow structure for the applications such as heat exchangers, the “support-less” condition must be achieved. Thus, extruded SiC-phenol resin compounds must be cured immediately after molding to keep the molded shapes. To increase the thermal conductivity of the SiC compounds, the combinations of commercial SiC powders with different average diameters were examined for increasing the volume fraction of SiC particles to the phenol resin. SiC compounds with optimized rheological properties for the modified FDM-type 3D-printer were successfully obtained.展开更多
In order to improve the performance of ceramic composite armor it is essential to know the mechanisms during each phase of the projectile–target interaction and their influence on the penetration resistance.Since the...In order to improve the performance of ceramic composite armor it is essential to know the mechanisms during each phase of the projectile–target interaction and their influence on the penetration resistance.Since the view on the crater zone and the tip of a projectile penetrating a ceramic is rapidly getting obscured by damaged material,a flash X-ray technique has to be applied in order to visualize projectile penetration.For this purpose,usually several flash X-ray tubes are arranged around the target and the radiographs are recorded on film.At EMI a flash X-ray imaging method has been developed,which provides up to eight flash radiographs in one experiment.A multi-anode 450 k V flash X-ray tube is utilized with this method.The radiation transmitted through the target is then detected on a fluorescent screen.The fluorescent screen converts the radiograph into an image in the visible wavelength range,which is photographed by means of a high-speed camera.This technique has been applied to visualize and analyze the penetration of 7.62 mm AP projectiles into three different types of Si C ceramics.Two commercial Si C grades and MICASIC(Metal Infiltrated Carbon derived Si C),a C-Si Si C ceramic developed by DLR,have been studied.The influences,not only of the ceramic but also the backing material,on dwell time and projectile erosion have been studied.Penetration curves have been determined and their relevance to the ballistic resistance is discussed.展开更多
Si3N4-SiC composite ceramics were fabricated by chemical vapor infiltration using porous Si3Na ceramic as preform. The average grain size of SiC was 30 nm. Relationship between SiC content and relative complex permitt...Si3N4-SiC composite ceramics were fabricated by chemical vapor infiltration using porous Si3Na ceramic as preform. The average grain size of SiC was 30 nm. Relationship between SiC content and relative complex permittivity of Si3Na-SiC within the frequency range of 8.2-12.4 GHz （X-band） was investigated. The average real part of relative complex permittivity ε′ of Si3N4-SiC increased from 3.7 to 14.9 and the relative imaginary part ε″ increased from 0.017 to 13.4 when the content of SiC increased from 0 to 10 vol.%. The Si3N4-SiC ceramic with 3 vol.% SiC achieved a reflection loss below -10 dB （90% absorption） at 8.0-11.4 GHz, and the minimum value was -27.1 dB at 9.8 GHz when the sample thickness was 2.5 mm. The excellent microwave absorbing abilities of Si3N4-SiC ceramic were attributed to the interfacial polarization at interface between Si3N4 and SiC and at grain boundary between SiC nanocrystals.展开更多
The microstructures and crack propagating characteristic of Si 3N 4 (μ)/SiC (n, w) composite ceramic were studied with AEM. The Si 3N 4 (μ)/SiC (n, w) composite ceramic consists of β Si 3N 4, β SiC, a smal...The microstructures and crack propagating characteristic of Si 3N 4 (μ)/SiC (n, w) composite ceramic were studied with AEM. The Si 3N 4 (μ)/SiC (n, w) composite ceramic consists of β Si 3N 4, β SiC, a small amount of α Si 3N 4 and α SiC, and amorphous phase. Most of Si 3N 4 grains were equiaxed crystal and also there were some bulky columnar ones. Most of SiC particles and SiC whiskers distributed at the Si 3N 4 grain boundaries and a few of smaller SiC particles in the Si 3N 4 grains. Most of amorphous structure was in the junction of several Si 3N 4 grains and thin amorphous layer was observed only at a few of Si 3N 4 boundaries. Failured cracks propagated mainly along the boundaries of the Si 3N 4 grains and partially passed through Si 3N 4 grains. The path of crack propagating might change, branching and twisting of the cracks might occur when the expanding crack meet the SiC particle and/or SiC whisker. Effect of the microstructure on strength and toughness of the composite ceramic was briefly discussed.展开更多
In recent decades,many additives with difierent characteristics have been applied to strengthen and toughen Al_2O_(3)一based ceramic cutting tool materials.Among them,SiC whiskers and SiC nanoparticles showed excellen...In recent decades,many additives with difierent characteristics have been applied to strengthen and toughen Al_2O_(3)一based ceramic cutting tool materials.Among them,SiC whiskers and SiC nanoparticles showed excellent performance in improving the material properties.W hile no attempts have been made to add SiC whiskers and SiC nanoparticles together into the ceramic matrix and the synergistically toughening efects of them have not been studied.An Al_2O_(3)一SiCw-SiCno advanced ceramic cutting tool material is fabricated by adding both one--dimensional SiC whiskers and zero--dimensional SiC nanoparticles into the Al_2O_(3)matrix with an efective dispersing and mixing process.The composites with 25 vo1%SiC whiskers and 25 vo1%SiC nanoparticles alone are also investegated for comparison purposes.Results show that the Al_2O_(3)一SiCw-SiCno composite with both 20 vo1%SiC whiskers and 5 vo1%SiC nanoparticles additives have much improved mechanical properties.The flexural strength of Al_2O_(3)-SiCw-SiCⅡD is 730~95 MPa and fracture toughness is 5.6±0.6 MPa’m.The toughening and strengthening mechanisms of SiC whiskers and nanoparticles are studied when they are added either individually or in combination.It is indicated that when SiC whiskers and nanoparticles are added together,the grains are further refined and homogenized,so that the microstructure and fracture mode ratio is modified.The SiC nanoparticles are found helpful to enhance the toughening efects of the SiC whiskers.The proposed research helps to enrich the types of ceramic cutting too1 and is benefit to expand the application range of ceramic cutting too1.展开更多
Ni/CeO_(2) catalysts(nCeO_(2):n_(Ni)=0,1,4,7,10)supported on SiC porous ce ramics for ethanol steam reforming(ESR)were investigated with respect to hydrogen production performance and growth of carbon deposition.The o...Ni/CeO_(2) catalysts(nCeO_(2):n_(Ni)=0,1,4,7,10)supported on SiC porous ce ramics for ethanol steam reforming(ESR)were investigated with respect to hydrogen production performance and growth of carbon deposition.The oxygen released from CeO_(2) enables the oxidation of CH_(x) species to serve as carbon precursors,thus providing Ni/CeO_(2) catalysts with stronger resistance to carbon deposition compared with Ni catalysts.The Ni/CeO_(2) catalysts prepared by inverse microemulsion and impregnation methods exhibit regular semicircular spherical shape on SiC porous ceramics.Under 500℃for 25 h of ESR reaction,the ethanol conversion rate over Ni/CeO_(2) catalysts(n_(CeO_(2)):n_(Ni)=7)is sustained up to 100%and H_(2) selectivity is essentially kept at 74%.The by-product selectivity declines stepwise with increasing content of CeO_(2),which is attributed to the adsorption and oxidation of CO and of CH_(x) species as CH_4 precursor from CeO_(2).The scanning electron microscopy(SEM)and transform electron microscopy(TEM)results reveal that further loading of CeO_(2) on the surface of Ni catalysts can alleviate both migration and sintering of Ni particles.Furthermore,carbon deposition on Ni/CeO_(2) catalysts preferentially outgrow filamentous rather than amorphous carbon,with a tendency for the latter to be more deactivated.展开更多
Joints between sintered silicon carbide （SSiC） were produced using a polysiloxane silicon resin YR3370 （GE Toshiba Silicones） as joining material. Samples were heat treated in a 99.99% nitrogen flux at temperature...Joints between sintered silicon carbide （SSiC） were produced using a polysiloxane silicon resin YR3370 （GE Toshiba Silicones） as joining material. Samples were heat treated in a 99.99% nitrogen flux at temperatures ranging from 1 100 ℃ to 1 300 ℃. Three point bending strength of the joint reached the maximum of 179 MPa as joined at 1 200℃. The joining layer is continuous, homogeneous and densified and has a thickness of 2 μm -5μm. The joining mechanism is that the amorphous silicon oxycarbide （SixOyCz） ceramic pyrolyzed from silicon resin YR3370 acts as an inorganic adhesive to SSiC substrate, which means the formation of the continuous Si-C bond structure between SixOyCz structure and SSiC substrate. Life prediction of the ceramic joint can be realized through the measurement of the critical time of the joint after the cyclic loading test.展开更多
An experimental investigation is carried out to machine SiC ceramic material through the method of high speed plane lapping with solid(fixed) abrasives after the critical condition of brittle-ductile transition is the...An experimental investigation is carried out to machine SiC ceramic material through the method of high speed plane lapping with solid(fixed) abrasives after the critical condition of brittle-ductile transition is theoretically analyzed. The results show that the material removal mechanism and the surface roughness are chiefly related to the granularity of abrasives for brittle materials such as SiC ceramic. It is easily realized to machine SiC ceramic in the ductile mode using W3.5 grit and a high efficiency, low cost and smooth surface with a surface roughness of R_a 2.4?nm can be achieved.展开更多
A novel temperature fluctuation synthesis/simultaneous densification process was developed for the preparation of Ti3SiC2 bulk ceramics. In this process. Si is used as an in-situ liquid forming phase and it is favorab...A novel temperature fluctuation synthesis/simultaneous densification process was developed for the preparation of Ti3SiC2 bulk ceramics. In this process. Si is used as an in-situ liquid forming phase and it is favorable for both the solid-liquid synthesis and the densification of Ti3SiC2 rainies. The present work demonstrated that the temperature fluctuation synthesis/simultaneous densification process is one of the most effective and simple methods for the preparation of Ti3SiC2 bulk materials providing relatively low synthesis temperature. short reaction time; and simultaneous synthesis and densification. This work also showed the capability to control the microstructure, e.g., the preferred orientation, of the bulk Ti3SiC2 materials simply by applying the hot pressing pressure at different Stages of the temperature fluctuation process. And textured Ti3SiC2 bulk materials with {002} faces of laminated Ti3SiC2 grains normal to the hot pressing axis were prepared.展开更多
SiC foam ceramic reinforced aluminum matrix composites(SFCAMCs)were prepared by squeeze casting aluminum alloy(Al-23Si)into the SiC foam ceramic with different pore sizes,and the corrosion behavior of the SFCAMCs was ...SiC foam ceramic reinforced aluminum matrix composites(SFCAMCs)were prepared by squeeze casting aluminum alloy(Al-23Si)into the SiC foam ceramic with different pore sizes,and the corrosion behavior of the SFCAMCs was studied in NaCl solutions.Static immersion corrosion tests were conducted at 20°C,50°C and 80°C,respectively.Corrosion morphology and products were analyzed by scanning electron microscope,energy dispersive system and X-ray diffraction.It was found that the corrosion rate of SFCAMCs increases as the temperature rising,and the bigger pore size of SiC foam ceramic reinforcement,the better corrosion resistance of SFCAMCs.展开更多
Alumina-based foam ceramic filters were fabricated by using alumina,SiC,magnesia powder as major materials.It has been found that this ceramic filter has a uniform macrostructure for filtering molten metals.The influe...Alumina-based foam ceramic filters were fabricated by using alumina,SiC,magnesia powder as major materials.It has been found that this ceramic filter has a uniform macrostructure for filtering molten metals.The influences of SiC and magnesia content,the sintering temperatures on ceramic properties were discussed.Alumina-based foam ceramic filters containing 2.2 mass% magnesia and 7.6 mass% SiC has a compressive strength of 1.36 MPa and a thermal shock resistance of 5 times.Its main phases after 1 hour sintering at 1 500℃ consist of alumina,silicon carbide,spinel and mullite.展开更多
In order to control the accumulation of SiC ceramic particles on the wall of the rotating chamber in the frame of a dry granulation process,the effect of the wall reverse speed on the mixing process is investigated.In...In order to control the accumulation of SiC ceramic particles on the wall of the rotating chamber in the frame of a dry granulation process,the effect of the wall reverse speed on the mixing process is investigated.In particular,an Euler-Euler two-phase flow model is used to analyze the dynamics of both SiC particles and air.The numerical results show that by setting a certain reverse rotating speed of the rotating chamber,the accumulation of SiC particles on the wall can be improved,i.e.,their direction of motion in proximity to the wall can be changed and particles can be forced to re-join the granulation process.Experimental tests conducted to verify the reliability of the numerical findings,demonstrate that when the reverse rotating speed of the rotating chamber is 4 r/min,the sphericity of SiC particles in the rotating chamber is the highest and the fluidity is the best possible one.展开更多
Mullite and corundum co-bonded SiC-based composite ceramics(SiC-mullite-Al2O3)were prepared by using SiC,calcined bauxite and kaolin via pressureless carbon-buried sintering.The low-cost SiC-based composite ceramics d...Mullite and corundum co-bonded SiC-based composite ceramics(SiC-mullite-Al2O3)were prepared by using SiC,calcined bauxite and kaolin via pressureless carbon-buried sintering.The low-cost SiC-based composite ceramics designed in this study are expected to be used as thermal storage materials in solar thermal power generation based on the high density and excellent thermal shock resistance.The influences of calcined bauxite addition and sintering temperature on the microstructures,phase compositions,and physical properties of the samples were investigated.Results demonstrated that the introduction of calcined bauxite containing two bonding phases greatly reduced the lowest sintering temperature to 1400℃.The SiC-mullite Al2O3 composite with 40 wt%calcined bauxite sintered at 1500℃exhibited optimum performance.The density and bending strength were 2.27 g·cm^-3 and 77.05 MPa.The bending strength increased by 24.58%and no cracks were observed after 30 thermal shock cycles,while general clay would reduce the thermal shock resistance of SiC.The SiC-mullite-Al2O3 composites with satisfied performance are expected to be used as thermal storage materials in solar thermal power generation systems.展开更多
This study examines the penetration of 12.7 mm armor piercing incendiary projectiles into SiC ceramic-fiber composite target plates.By observing the recovered projectile and the overall damage morphology of the cerami...This study examines the penetration of 12.7 mm armor piercing incendiary projectiles into SiC ceramic-fiber composite target plates.By observing the recovered projectile and the overall damage morphology of the ceramic-fiber composite target plates.Additionally,multi-level screening and weighing of the recovered projectile and ceramic fragments revealed that the mass distribution of the projectile and ceramic fragments under different backing structures conforms to a powerlaw distribution.Experimental results indicate that for single laminate as the backing,the fragmentation of the projectile and ceramics is highest when T300 is the material.Incorporating a T300 transition layer between the SiC ceramic and aramid fibers(Kevlar)or ultra-high molecular weight polyethylene(UHMWPE)increases the fragmentation of the projectile and ceramics,leading to increased energy absorption.The projectile’s head mainly exhibits pulverized abrasive fragmentation,while larger projectile fragments primarily result from shear and tensile stress-induced shear-tensile failure fractures.The primary damage mode of ceramics under high-speed impact is the expansion of ceramic cones and radial cracks.The main form of damage in UHMWPE laminate is interlayer separation caused by tensile waves,permanent plastic deformation at the back protrusion,and perforation failure primarily due to shear waves.The damage mode of Kevlar laminate is similar to that of UHMWPE,with the distinction being that Kevlar laminate primarily exhibits perforation failure caused by tensile waves.Carbon fiber T300 laminate damage mainly consists of cross-shaped brittle fractures caused by shear waves.展开更多
Porous C/C-SiC composites were prepared through a two-step chemical vapor infiltration process,and a multi-interlayer joint of Li20-MgO-Al2O3-SiO2（LMAS） was applied to join C/C-SiC composites and lithium aluminum si...Porous C/C-SiC composites were prepared through a two-step chemical vapor infiltration process,and a multi-interlayer joint of Li20-MgO-Al2O3-SiO2（LMAS） was applied to join C/C-SiC composites and lithium aluminum silicate（LAS） glass ceramics by means of a vacuum hot-pressing technique.Plenty of SiC whiskers were generated in the pores of low-density C/C composites during chemical vapor deposition process,which is essentia! to form a zigzag interface structure between C/C-SiC substrate and the LMAS interlayer.The average shear strength of the LMAS joint was improved from 12.17 to 19.91 MPa after changing the composites from high-density C/C composites（1.75 g/cm3） with a CVD-SiC coating to the C/C-SiC composites with a low density（1.48 g/cm3）.The improvement of the joint strength is mainly attributed to the formation of the inlay structure at the SiC-C/C and SiC-LMAS interfaces.展开更多
文摘Si/SiC ceramic composite and lnvar alloy were successfidly joined by vacuum brazing using Ti5OCu-W filler metals into which W was added to release the thermal stress of the brazed joint. Microstructures of the brazed joints were irwestigated by scanning electron micrascope （SEM） and energy dispersive spectrometer （EDS）. The mechanical properties of the brazed joints were measured by shearing tests. The results showed that the brazed joints were composed of Ti-Cu phase, W phase and Ti-Si phase. W had no effect on the wettability and mobility of the .filler metals. The growth of Ti2 Cu phase was restrained, and the reaction between ceramic composite and filler metals was weakened. The specimen, brazed at 970°C for 5 rain, had the maximum shear strength of 108 MPa at room temperature.
基金National Natural Science Foundation of China (51572112, 511172177) the Natural Science Foundation of Jiangsu Province (BK20151340)+2 种基金 theSix Talent Peaks Project of Jiangsu Province (2014-XL-002) the Post Doctorial Science Foundation of China (2014M551512) the Innovation/EntrepreneurshipProgram of Jiangsu Province ([2013]477, [2015]26)
文摘Three kinds of Mo-Ni-Si metallized coatings with various chemical compositions were deposited on SiC ceramic substrates by vacuum fusion sintering process, and the phase compositions of the coatings and their interface microstructures were analyzed. The wetting and spreading properties of molten Ag on the coated SiC ceramic substrates were investigated by the sessile drop technique, and the interfacial behavior of the Ag/coated SiC systems was analyzed. The results show that the coatings are mainly composed of Mo5Si3, MoSi2, Ni2Si, NiSi2 and MoNiSi. The tetragonal MoSi2 grains on the coating surface disappear gradually with the concentration of Mo increasing from 20 at% to 40 at%. The final contact angles of Ag/coated SiC systems at 1000 ℃ for holding 30 min are 45°, 79° and 85° for the coating compositions of Mo20-Ni32-Si48, Mo30-Ni28-Si42 and Mo40-Ni24-Si36, respectively. This result could be closely related to the interactions between the Ag drop and the microstructures of the three Mo-Ni-Si coatings. No obvious reaction layers are found at all the coating/substrate interfaces before and after the wetting tests.
基金supported financially by the National Natural Science Foundation of China (Nos. U1435206 and 51672064)the Beijing Municipal Science & Technology Commission (No. D161100002416001)
文摘Researching for interphase materials that can protect SiC fibers from oxygen and water vapor attacks has become one of the most important issues for the applications of SiC_f/SiC composites in high-temperature combustion environment. However, such kinds of interphase materials are not available yet. Herein,we report theoretically predicted properties of two promising interphase materials Y_5Si_3 C and Y_3Si_2C_2.Although crystallizing in different structures, they share the common features of layered structure,anisotropic chemical bonding, anisotropic electrical and mechanical properties, and low shear deformation resistance. The bulk moduli for Y_5Si_3C and Y_3Si_2C_2 are 78 and 93 GPa, respectively; while their shear moduli are 52 and 50GPa, respectively. The maximum to minimum Young's modulus ratios are1.44 for Y_5Si_3C and 3.27 for Y_3Si_2C_2. Based on the low shear deformation resistance and low Pugh's ratios(G/B = 0.666 forY_5Si_3C and 0.537 for Y_3Si_2C_2; G: shear modulus; B: bulk modulus), they are predicted as damage tolerant and soft ceramics with predicted Vickers hardness of 9.6 and 6.9 GPa, respectively.The cleavage plane and possible slip systems are(000 l) and(0001)[1120] and(1010)[0001] forY_5Si_3C,and those for Y_3Si_2C_2 are {h00} and(010)[101]. Since the oxidation products are water-vapor resistant Y2 Si2 O7, Y2 SiO5 and/or Y_2 O_3 upon oxidation, and the volume expansions are ca 140% and ca 26% for Y_5Si_3C and Y_3Si_2C_2, they are expected to seal the interfacial cracks in SiC_f/SiC composites. The unique combination of easy cleavage, low shear deformation resistance, volume expansions upon oxidation, and the resistance of the oxidation products to water vapor attack warrant them promising as interphase materials of SiC_f/SiC composites for water-vapor laden environment applications.
基金supported by National Science and Technology Major Project(no.2017-Ⅶ-0008-0102)National Natural Science Foundation of China(no.51975230)Fundamental Research Funds for the Central Universities(nos.2019kfy XMPY020,2020kfy FPZX003,2018KFYYXJJ030,2019kfy XKJC011)。
文摘Silica-based ceramic cores have been widely used to fabricate aero-engine hollow blades due to their moderate high temperature mechanical properties and excellent leachability.In this study,silica-based ceramics with SiC fiber addition were prepared via stereolithography,and the influence of SiC fiber content on mechanical properties of the obtained silica-based ceramics was investigated.With the increase of SiC fiber content,linear shrinkage gradually decreased,while room temperature flexural strength and high temperature flexural strength first increased and then decreased.As SiC fiber content increased to 4.0 wt%,linear shrinkage was reduced to 0.62%resulting from the oxidation of SiC.Furthermore,room temperature flexural strength was improved from 11.79 MPa to 23.83 MPa and high temperature flexural strength was enhanced from 15.64 MPa to 34.62 MPa with 4.0 wt%SiC fiber addition due to the reinforcement of fibers and the enhancedβ-cristobalite content,which meets the need of ceramic cores.Therefore,it demonstrates the capability of fabricating high-performance and high-precision silica-based ceramic cores reinforced by SiC fibers via stereolithography for rapid manufacturing of hollow blades.
文摘Silicon carbide (SiC) ceramics have excellent properties and widely used for high temperature applications. So far, joining techniques have been applied to fabricate large SiC ceramics with complicated shapes. In this work, the additive manufacturing (AM) technique was examined to fabricated SiC ceramics with complicated hollow structures using the Fused Deposition Modeling (FDM) type 3D-printer. To mold the hollow structure for the applications such as heat exchangers, the “support-less” condition must be achieved. Thus, extruded SiC-phenol resin compounds must be cured immediately after molding to keep the molded shapes. To increase the thermal conductivity of the SiC compounds, the combinations of commercial SiC powders with different average diameters were examined for increasing the volume fraction of SiC particles to the phenol resin. SiC compounds with optimized rheological properties for the modified FDM-type 3D-printer were successfully obtained.
基金financial support of the study by the Bundeswehr Research Institute for Materials, Fuels and Lubricants (WIWe B) (grant number E/E210/AB015/9F120)
文摘In order to improve the performance of ceramic composite armor it is essential to know the mechanisms during each phase of the projectile–target interaction and their influence on the penetration resistance.Since the view on the crater zone and the tip of a projectile penetrating a ceramic is rapidly getting obscured by damaged material,a flash X-ray technique has to be applied in order to visualize projectile penetration.For this purpose,usually several flash X-ray tubes are arranged around the target and the radiographs are recorded on film.At EMI a flash X-ray imaging method has been developed,which provides up to eight flash radiographs in one experiment.A multi-anode 450 k V flash X-ray tube is utilized with this method.The radiation transmitted through the target is then detected on a fluorescent screen.The fluorescent screen converts the radiograph into an image in the visible wavelength range,which is photographed by means of a high-speed camera.This technique has been applied to visualize and analyze the penetration of 7.62 mm AP projectiles into three different types of Si C ceramics.Two commercial Si C grades and MICASIC(Metal Infiltrated Carbon derived Si C),a C-Si Si C ceramic developed by DLR,have been studied.The influences,not only of the ceramic but also the backing material,on dwell time and projectile erosion have been studied.Penetration curves have been determined and their relevance to the ballistic resistance is discussed.
基金financial support from the National University Student Innovation Program fund (No. 101069911)supported by the Research Fund of State Key Laboratory of Solidification Processing in Northwestern Polytechnical University (No. KB200920)+1 种基金the China Postdoctoral Science Foundation (No. 20110491683)the 111 Project(B08040)
文摘Si3N4-SiC composite ceramics were fabricated by chemical vapor infiltration using porous Si3Na ceramic as preform. The average grain size of SiC was 30 nm. Relationship between SiC content and relative complex permittivity of Si3Na-SiC within the frequency range of 8.2-12.4 GHz （X-band） was investigated. The average real part of relative complex permittivity ε′ of Si3N4-SiC increased from 3.7 to 14.9 and the relative imaginary part ε″ increased from 0.017 to 13.4 when the content of SiC increased from 0 to 10 vol.%. The Si3N4-SiC ceramic with 3 vol.% SiC achieved a reflection loss below -10 dB （90% absorption） at 8.0-11.4 GHz, and the minimum value was -27.1 dB at 9.8 GHz when the sample thickness was 2.5 mm. The excellent microwave absorbing abilities of Si3N4-SiC ceramic were attributed to the interfacial polarization at interface between Si3N4 and SiC and at grain boundary between SiC nanocrystals.
文摘The microstructures and crack propagating characteristic of Si 3N 4 (μ)/SiC (n, w) composite ceramic were studied with AEM. The Si 3N 4 (μ)/SiC (n, w) composite ceramic consists of β Si 3N 4, β SiC, a small amount of α Si 3N 4 and α SiC, and amorphous phase. Most of Si 3N 4 grains were equiaxed crystal and also there were some bulky columnar ones. Most of SiC particles and SiC whiskers distributed at the Si 3N 4 grain boundaries and a few of smaller SiC particles in the Si 3N 4 grains. Most of amorphous structure was in the junction of several Si 3N 4 grains and thin amorphous layer was observed only at a few of Si 3N 4 boundaries. Failured cracks propagated mainly along the boundaries of the Si 3N 4 grains and partially passed through Si 3N 4 grains. The path of crack propagating might change, branching and twisting of the cracks might occur when the expanding crack meet the SiC particle and/or SiC whisker. Effect of the microstructure on strength and toughness of the composite ceramic was briefly discussed.
基金Supported by National Natural Science Foundation of China(Grant No.51175305)
文摘In recent decades,many additives with difierent characteristics have been applied to strengthen and toughen Al_2O_(3)一based ceramic cutting tool materials.Among them,SiC whiskers and SiC nanoparticles showed excellent performance in improving the material properties.W hile no attempts have been made to add SiC whiskers and SiC nanoparticles together into the ceramic matrix and the synergistically toughening efects of them have not been studied.An Al_2O_(3)一SiCw-SiCno advanced ceramic cutting tool material is fabricated by adding both one--dimensional SiC whiskers and zero--dimensional SiC nanoparticles into the Al_2O_(3)matrix with an efective dispersing and mixing process.The composites with 25 vo1%SiC whiskers and 25 vo1%SiC nanoparticles alone are also investegated for comparison purposes.Results show that the Al_2O_(3)一SiCw-SiCno composite with both 20 vo1%SiC whiskers and 5 vo1%SiC nanoparticles additives have much improved mechanical properties.The flexural strength of Al_2O_(3)-SiCw-SiCⅡD is 730~95 MPa and fracture toughness is 5.6±0.6 MPa’m.The toughening and strengthening mechanisms of SiC whiskers and nanoparticles are studied when they are added either individually or in combination.It is indicated that when SiC whiskers and nanoparticles are added together,the grains are further refined and homogenized,so that the microstructure and fracture mode ratio is modified.The SiC nanoparticles are found helpful to enhance the toughening efects of the SiC whiskers.The proposed research helps to enrich the types of ceramic cutting too1 and is benefit to expand the application range of ceramic cutting too1.
基金Project supported by the Natural Science Foundation of Hunan Province,China (2022JJ30133)。
文摘Ni/CeO_(2) catalysts(nCeO_(2):n_(Ni)=0,1,4,7,10)supported on SiC porous ce ramics for ethanol steam reforming(ESR)were investigated with respect to hydrogen production performance and growth of carbon deposition.The oxygen released from CeO_(2) enables the oxidation of CH_(x) species to serve as carbon precursors,thus providing Ni/CeO_(2) catalysts with stronger resistance to carbon deposition compared with Ni catalysts.The Ni/CeO_(2) catalysts prepared by inverse microemulsion and impregnation methods exhibit regular semicircular spherical shape on SiC porous ceramics.Under 500℃for 25 h of ESR reaction,the ethanol conversion rate over Ni/CeO_(2) catalysts(n_(CeO_(2)):n_(Ni)=7)is sustained up to 100%and H_(2) selectivity is essentially kept at 74%.The by-product selectivity declines stepwise with increasing content of CeO_(2),which is attributed to the adsorption and oxidation of CO and of CH_(x) species as CH_4 precursor from CeO_(2).The scanning electron microscopy(SEM)and transform electron microscopy(TEM)results reveal that further loading of CeO_(2) on the surface of Ni catalysts can alleviate both migration and sintering of Ni particles.Furthermore,carbon deposition on Ni/CeO_(2) catalysts preferentially outgrow filamentous rather than amorphous carbon,with a tendency for the latter to be more deactivated.
基金National Key Fundamental R&D Plan (2004CB217808)National Natural Science Foundation of China (20271037)
文摘Joints between sintered silicon carbide （SSiC） were produced using a polysiloxane silicon resin YR3370 （GE Toshiba Silicones） as joining material. Samples were heat treated in a 99.99% nitrogen flux at temperatures ranging from 1 100 ℃ to 1 300 ℃. Three point bending strength of the joint reached the maximum of 179 MPa as joined at 1 200℃. The joining layer is continuous, homogeneous and densified and has a thickness of 2 μm -5μm. The joining mechanism is that the amorphous silicon oxycarbide （SixOyCz） ceramic pyrolyzed from silicon resin YR3370 acts as an inorganic adhesive to SSiC substrate, which means the formation of the continuous Si-C bond structure between SixOyCz structure and SSiC substrate. Life prediction of the ceramic joint can be realized through the measurement of the critical time of the joint after the cyclic loading test.
文摘An experimental investigation is carried out to machine SiC ceramic material through the method of high speed plane lapping with solid(fixed) abrasives after the critical condition of brittle-ductile transition is theoretically analyzed. The results show that the material removal mechanism and the surface roughness are chiefly related to the granularity of abrasives for brittle materials such as SiC ceramic. It is easily realized to machine SiC ceramic in the ductile mode using W3.5 grit and a high efficiency, low cost and smooth surface with a surface roughness of R_a 2.4?nm can be achieved.
基金the National Outstanding YOung Scientist Foundation Under Grant !No.59925208 the National Natural Science Foundation of China
文摘A novel temperature fluctuation synthesis/simultaneous densification process was developed for the preparation of Ti3SiC2 bulk ceramics. In this process. Si is used as an in-situ liquid forming phase and it is favorable for both the solid-liquid synthesis and the densification of Ti3SiC2 rainies. The present work demonstrated that the temperature fluctuation synthesis/simultaneous densification process is one of the most effective and simple methods for the preparation of Ti3SiC2 bulk materials providing relatively low synthesis temperature. short reaction time; and simultaneous synthesis and densification. This work also showed the capability to control the microstructure, e.g., the preferred orientation, of the bulk Ti3SiC2 materials simply by applying the hot pressing pressure at different Stages of the temperature fluctuation process. And textured Ti3SiC2 bulk materials with {002} faces of laminated Ti3SiC2 grains normal to the hot pressing axis were prepared.
基金Project(00008713)supported by the Program of the Science and Technology Creative Team of Universities in Jiangxi,ChinaProject(2013-KLP-04)supported by the Open Foundation of Jiangxi Key Laboratory for Advanced Copper and Tungsten Materials,China
文摘SiC foam ceramic reinforced aluminum matrix composites(SFCAMCs)were prepared by squeeze casting aluminum alloy(Al-23Si)into the SiC foam ceramic with different pore sizes,and the corrosion behavior of the SFCAMCs was studied in NaCl solutions.Static immersion corrosion tests were conducted at 20°C,50°C and 80°C,respectively.Corrosion morphology and products were analyzed by scanning electron microscope,energy dispersive system and X-ray diffraction.It was found that the corrosion rate of SFCAMCs increases as the temperature rising,and the bigger pore size of SiC foam ceramic reinforcement,the better corrosion resistance of SFCAMCs.
基金The project is supported by National Natural Science Foundation of China:50334030PhD Fund of Liaoning Province:20041010.
文摘Alumina-based foam ceramic filters were fabricated by using alumina,SiC,magnesia powder as major materials.It has been found that this ceramic filter has a uniform macrostructure for filtering molten metals.The influences of SiC and magnesia content,the sintering temperatures on ceramic properties were discussed.Alumina-based foam ceramic filters containing 2.2 mass% magnesia and 7.6 mass% SiC has a compressive strength of 1.36 MPa and a thermal shock resistance of 5 times.Its main phases after 1 hour sintering at 1 500℃ consist of alumina,silicon carbide,spinel and mullite.
基金the National Natural Science Foundation of China(Grant No.51964022).
文摘In order to control the accumulation of SiC ceramic particles on the wall of the rotating chamber in the frame of a dry granulation process,the effect of the wall reverse speed on the mixing process is investigated.In particular,an Euler-Euler two-phase flow model is used to analyze the dynamics of both SiC particles and air.The numerical results show that by setting a certain reverse rotating speed of the rotating chamber,the accumulation of SiC particles on the wall can be improved,i.e.,their direction of motion in proximity to the wall can be changed and particles can be forced to re-join the granulation process.Experimental tests conducted to verify the reliability of the numerical findings,demonstrate that when the reverse rotating speed of the rotating chamber is 4 r/min,the sphericity of SiC particles in the rotating chamber is the highest and the fluidity is the best possible one.
基金Funded by the National Key Research and Development Program of Science and Technology of China(No.2018YFB1501002).
文摘Mullite and corundum co-bonded SiC-based composite ceramics(SiC-mullite-Al2O3)were prepared by using SiC,calcined bauxite and kaolin via pressureless carbon-buried sintering.The low-cost SiC-based composite ceramics designed in this study are expected to be used as thermal storage materials in solar thermal power generation based on the high density and excellent thermal shock resistance.The influences of calcined bauxite addition and sintering temperature on the microstructures,phase compositions,and physical properties of the samples were investigated.Results demonstrated that the introduction of calcined bauxite containing two bonding phases greatly reduced the lowest sintering temperature to 1400℃.The SiC-mullite Al2O3 composite with 40 wt%calcined bauxite sintered at 1500℃exhibited optimum performance.The density and bending strength were 2.27 g·cm^-3 and 77.05 MPa.The bending strength increased by 24.58%and no cracks were observed after 30 thermal shock cycles,while general clay would reduce the thermal shock resistance of SiC.The SiC-mullite-Al2O3 composites with satisfied performance are expected to be used as thermal storage materials in solar thermal power generation systems.
文摘This study examines the penetration of 12.7 mm armor piercing incendiary projectiles into SiC ceramic-fiber composite target plates.By observing the recovered projectile and the overall damage morphology of the ceramic-fiber composite target plates.Additionally,multi-level screening and weighing of the recovered projectile and ceramic fragments revealed that the mass distribution of the projectile and ceramic fragments under different backing structures conforms to a powerlaw distribution.Experimental results indicate that for single laminate as the backing,the fragmentation of the projectile and ceramics is highest when T300 is the material.Incorporating a T300 transition layer between the SiC ceramic and aramid fibers(Kevlar)or ultra-high molecular weight polyethylene(UHMWPE)increases the fragmentation of the projectile and ceramics,leading to increased energy absorption.The projectile’s head mainly exhibits pulverized abrasive fragmentation,while larger projectile fragments primarily result from shear and tensile stress-induced shear-tensile failure fractures.The primary damage mode of ceramics under high-speed impact is the expansion of ceramic cones and radial cracks.The main form of damage in UHMWPE laminate is interlayer separation caused by tensile waves,permanent plastic deformation at the back protrusion,and perforation failure primarily due to shear waves.The damage mode of Kevlar laminate is similar to that of UHMWPE,with the distinction being that Kevlar laminate primarily exhibits perforation failure caused by tensile waves.Carbon fiber T300 laminate damage mainly consists of cross-shaped brittle fractures caused by shear waves.
基金funding supported from the National Natural Science Foundation of China(Grant Nos.51221001 and 51222207)the "111" Project(Grant No.B08040)the Foundation of the National Excellent Doctoral Dissertation of China(No.201036)
文摘Porous C/C-SiC composites were prepared through a two-step chemical vapor infiltration process,and a multi-interlayer joint of Li20-MgO-Al2O3-SiO2（LMAS） was applied to join C/C-SiC composites and lithium aluminum silicate（LAS） glass ceramics by means of a vacuum hot-pressing technique.Plenty of SiC whiskers were generated in the pores of low-density C/C composites during chemical vapor deposition process,which is essentia! to form a zigzag interface structure between C/C-SiC substrate and the LMAS interlayer.The average shear strength of the LMAS joint was improved from 12.17 to 19.91 MPa after changing the composites from high-density C/C composites（1.75 g/cm3） with a CVD-SiC coating to the C/C-SiC composites with a low density（1.48 g/cm3）.The improvement of the joint strength is mainly attributed to the formation of the inlay structure at the SiC-C/C and SiC-LMAS interfaces.
