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1.
Chemical-Vapor-Infiltrated Silicon Nitride, Boron Nitride, and Silicon Carbide Matrix Composites 总被引:1,自引:0,他引:1
Composites of carbon/chemical-vapor-deposited (CVD) Si3 N4 , carbon/CVD BN, mullite/CVD SiC, and SiC yarn/CVD SiC were prepared to determine if there were inherent toughness in these systems. The matrices were deposited at high enough temperatures to ensure that they were crystalline, which should make them more stable at high temperatures. The fiber-matrix bonding in the C/Si3 N4 composite appeared to be too strong; the layers of BN in the matrix of the C/BN were too weakly bonded; and the mullite/SiC composite was not as tough as the SiC/SiC composites. Only the SiC yarn/CVD SiC composite exhibited both strength and toughness. 相似文献
2.
Hironori Kodama Hiroshi Sakamoto Tadahiko Miyoshi 《Journal of the American Ceramic Society》1989,72(4):551-558
SiC-monofilament-reinforced SiC or Si3 N4 matrix composites were fabricated by hot-pressing, and their mechanical properties and effects of filaments and filament coating layers were studied. Relationships between frictional stress of filament/matrix interface and fracture toughness of SiC monofilament/Si3 N4 matrix composites were also investigated. As a result, it was confirmed experimentally that in the case of composites fractured with filament pullout, the fracture toughness increased as the frictional stress increased. On the other hand, when frictional stress was too large (>about 80 MPa) for the filament to be pulled out, fracture toughnesses of the composites were almost the same and not so much improved over that of Si3 N4 monolithic ceramics. The filament coating layers were found to have a significant effect on the frictional stress of the SiC monofilament/Si3 N4 matrix interface and consequently the fracture toughness of the composites. Also the crack propagation behavior in the SiC monofilament/Si3 N4 matrix composites was observed during flexural loading and cyclic loading tests by an in situ observation apparatus consisting of an SEM and a bending machine. The filament effect which obstructed crack propagation was clearly observed. Fatigue crack growth was not detected after 300 cyclic load applications. 相似文献
3.
Ellen Y. Sun Steven R. Nutt John J. Brennan 《Journal of the American Ceramic Society》1997,80(1):264-266
Interfaces in SK-fiber-reinforced glass-ceramic matrix composites were modified by applying different coatings to the fibers and varying the coating thickness. Coatings of SiC/BN, Si3 N4 /BN, and BN were applied to the fibers by CVD prior to composite fabrication. Interfacial microstructures were characterized using high-resolution and analytical transmission electron microscopy. Oxidation of the SiC fibers during composite fabrication was suppressed by the fiber coatings, provided that the coatings were sufficiently thick to prevent oxygen diffusion from the matrix. The SiC/RN and BN coatings were stable during high-temperature exposures, while the Si3 N4 /BN coating underwent chemical reactions. 相似文献
4.
Chang-an Wang Yong Huang Qingfeng Zan Linhua Zou Shengyou Cai 《Journal of the American Ceramic Society》2002,85(10):2457-2461
Based on a biomimetic design, Si3 N4 /BN composites with laminated structures have been prepared and investigated through composition control and structure design. To further improve the mechanical properties of the composites, Si3 N4 matrix layers were reinforced by SiC whiskers and BN separating layers were modified by adding Si3 N4 or Al2 O3 . The results showed that the addition of SiC whiskers in the Si3 N4 matrix layers could greatly improve the apparent fracture toughness (reaching 28.1 MPa·m1/2 ), at the same time keeping the higher bending strength (reaching 651.5 MPa) of the composites. Additions of 50 wt% Al2 O3 or 10 wt% Si3 N4 to BN interfacial layers had a beneficial effect on the strength and toughness of the laminated Si3 N4 /BN composites. Through observation of microstructure by SEM, multilevel toughening mechanisms contributing to high toughness of the laminated Si3 N4 /BN composites were present as the first-level toughening mechanisms from BN interfacial layers as crack deflection, bifurcation, and pull-out of matrix sheets, and the secondary toughening mechanism from whiskers in matrix layers. 相似文献
5.
Jae Young Choi Chong Hee Kim Do Kyung Kim 《Journal of the American Ceramic Society》1999,82(10):2665-2671
The synthesis and structure of a monodispersed spherical Si3 N4 /SiC nanocomposite powder have been studied. The Si3 N4 /SiC nanocomposite powder was synthesized by heating under argon a spherical Si3 N4 /C powder. The spherical Si3 N4 /C powder was prepared by heating a spherical organosilica powder in a nitrogen atmosphere and was composed of a mixture of nanosized Si3 N4 and free carbon particles. During the heat treatment at 1450°C, the Si3 N4 /C powder became a Si3 N4 /SiC composite powder and finally a SiC powder after 8 h, while retaining its spherical shape. The composition of the Si3 N4 /SiC composite powder changed with the duration of the heat treatment. The results of TEM, SEM, and selected area electron diffraction showed that the Si3 N4 /SiC composite powder was composed of homogeneously distributed nanosized Si3 N4 and SiC particles. 相似文献
6.
A carbothermal reaction of silica–phenol resin hybrid gels prepared from a two-step sol–gel process was conducted in atmospheric nitrogen. The gels were first pyrolyzed into homogeneous silica–carbon mixtures during heating and subsequently underwent a carbothermal reaction at higher temperatures. Using a gel-derived precursor with a C/SiO2 molar ratio higher than 3.0, Si3 N4 /SiC nanocomposite powders were produced at 1500°–1550°C, above the Si3 N4 –SiC boundary temperature. The predominant phase was Si3 N4 at 1500°C, and SiC at 1550°C. The Si3 N4 and SiC phase contents were adjustable by varying the temperature in this narrow range. The phase contents could also be adjusted by changing the starting carbon contents, or by its combination with varying reaction temperature. A two-stage process, i.e., a reaction first at 1550°C and then at 1500°C, offered another means of simple and effective control of the phase composition: the Si3 N4 and SiC contents varied almost linearly with the variation of the holding time at 1550°C. The SiC was nanosized (∼13 nm, Scherrer method) formed via a solid–gas reaction, while the Si3 N4 has two morphologies: elongated microsized crystals and nanosized crystallites, with the former crystallized via a gaseous reaction, and the latter formed via a solid–gas reaction. The addition of a Si3 N4 powder as a seed to the starting gel effectively reduced the size of the Si3 N4 produced. 相似文献
7.
Jianren Zeng Yoshinari Miyamoto Osamu Yamada 《Journal of the American Ceramic Society》1991,74(9):2197-2200
Fine Si3 N4 -SiC composite powders were synthesized in various SiC compositions to 46 vol% by nitriding combustion of silicon and carbon. The powders were composed of α-Si3 N4 , β-Si3 N4 , and β-SiC. The reaction analysis suggested that the SiC formation is assisted by the high reaction heat of Si nitridation. The sintered bodies consisted of uniformly dispersed grains of β-Si3 N4 , β-SiC, and a few Si2 N2 O. 相似文献
8.
Synthesis of Silicon Nitride/Silicon Carbide Nanocomposite Powders through Partial Reduction of Silicon Nitride by Pyrolyzed Carbon 总被引:1,自引:0,他引:1
An alternative method to incorporate nanometer-sized silicon carbide (SiC) particles into silicon nitride (Si3 N4 ) powder was proposed and investigated experimentally. Novolac-type phenolic resin was dissolved in ethanol and mixed with Si3 N4 powder. After drying and curing, the resin was converted to reactive carbon via pyrolysis. Si3 N4 powder was partially reduced carbothermally using the pyrolyzed carbon, and nanometer-sized SiC particles were produced in situ at 1530°-1610°C in atmospheric nitrogen. At temperatures <1550°C, the reduction rate was low and the SiC particles were very small; no SiC whiskers or barlike SiC was observed. At 1600°C, the reduction rate was high and the reaction was close to completion after only 10 min, with the appearance of SiC whiskers as well as curved, barlike, and equiaxial SiC, all of which were dozens of nanometers in diameter; this size is greater than that at observed temperatures <1550°C. A longer soaking time at 1600°C led to agglomerates. SiC particles were close to the surface of the Si3 N4 particles. The SiC content could be adjusted by changing the carbon content before reduction and the reduction temperature. A reaction mechanism that involved the decomposition of Si3 N4 has been proposed. 相似文献
9.
Chen-Feng Chan Bernard B. Argent William E. Lee 《Journal of the American Ceramic Society》1998,81(12):3177-3188
The microstructures of Al2 O3 –SiO2 –SiC–C refractory matrices with aluminum, silicon, Si3 N4 , BN, B2 O3 , and B4 C additives are characterized before and after a crucible slag test, and the phases present are compared to those expected at thermodynamic equilibrium. The carbon content dominates the resistance to CaO–MgO–Al2 O3 –SiO2 slag penetration, while the viscosity of liquid phases present has a significant influence when the matrix carbon contents are similar. Silicon and Si3 N4 additives reduce slag penetration resistance because of indirect oxidation of carbon to form SiC. B4 C, in particular, and B2 O3 also reduce slag penetration resistance because of formation of a more fluid boron-containing liquid, while aluminum and BN addition have no significant effect. Carbon and BN hardly react with the slag, while SiC partially reacts with it, leading to deposition of carbon as a dense layer. Corundum present in the refractories also readily dissolves in the slag. Microstructurally, slag penetration resistance is associated with the dense carbon layer located at the slag-refractory interface. 相似文献
10.
Fabrication of Low-Shrinkage, Porous Silicon Nitride Ceramics by Addition of a Small Amount of Carbon 总被引:4,自引:0,他引:4
Jian-Feng Yang Guo-Jun Zhang Tatsuki Ohji 《Journal of the American Ceramic Society》2001,84(7):1639-1641
Successful net-shape sintering offers a significant advantage for producing large or complicated products. Porous Si3 N4 ceramics with very low shrinkage were developed, in the present investigation, by the addition of a small amount of carbon. Carbon powders (1–5 vol%) of two types, with different mean particle sizes (13 nm and 5 μm), were added to α-Si3 N4 −5 wt% Y2 O3 powders. SiC nanoparticles formed through reaction of the added carbon with SiO2 on the Si3 N4 surface or with the Si3 N4 particles themselves. Such reaction-formed SiC nanoparticles apparently had an effective reinforcing effect, as in nanocomposites. Sintered Si3 N4 porous ceramics with a high porosity of 50%–60%, a very small linear shrinkage of ∼2%–3%, and a strength of ∼100 MPa were obtained. 相似文献
11.
Silicon Nitride Based Ceramic Nanocomposites 总被引:7,自引:0,他引:7
Xiaoqing Pan Joachim Mayer Manfred Rühle Koichi Niihara 《Journal of the American Ceramic Society》1996,79(3):585-590
Nanocomposites (Si3 N4 /SiC) were studied by combined high-resolution transmission electron microscopy and electron energy-loss spectroscopic imaging (ESI) techniques. In ESI micrographs three types of crystalline grains were distinguished: Si3 N4 matrix grains (0.5 μΩ), nanosized SiC particles (<100 nm) embedded in the Si3 N4 , and large SiC particles (100–200 nm) at grain boundary regions (intergranular particles). Amorphous films were found both at Si3 N4 grain boundaries and at phase boundaries between Si3 N4 and SiC. The Si3 N4 grain boundary film thickness varied from 1 to 2. 5 nm. Two kinds of embedded SiC particles were observed: type A has a special orientation with respect to the matrix, and type B possesses a random orientation with respect to the matrix. The surfaces of type B particles are completely covered by an amorphous phase. The existence of the amorphous film between the matrix and the particles of type A depends on the lattice mismatch across the interface. The mechanisms of nucleation and growth of Ω-Si3 N4 grains are discussed on the basis of these experimental results. 相似文献
12.
Yoon-Suk Oh Woo-Seok Cho Chang-Sam Kim Dae Soon Lim Deock-Soo Cheong 《Journal of the American Ceramic Society》1999,82(4):1076-1078
We have synthesized Si3 N4 /SiC nanocomposites using a commercial polymer. Formation behavior of SiC nanoparticles has been studied using X-ray photoelectron spectroscopy (XPS). Based on the XPS results, we concluded that SiC nanoparticles were formed by a chemical reaction of Si provided from Si3 N4 with free carbon obtained by pyrolysis of a polymer around 1300°C. The presence of CN x compounds in samples processed in an Ar atmosphere supported our explanation. 相似文献
13.
Takafumi Kusunose Tohru Sekino Yong Ho Choa Koichi Niihara 《Journal of the American Ceramic Society》2002,85(11):2678-2688
A chemical process for fabrication of Si3 N4 /BN nanocomposite was devised to improve the mechanical properties. Si3 N4 /BN nanocomposites containing 0 to 30 vol% hexagonal BN ( h -BN) were successfully fabricated by hot-pressing α-Si3 N4 powders, on which turbostratic BN ( t -BN) with a disordered layer structure was partly coated. The t -BN coating on α-Si3 N4 particles was prepared by reducing and heating α-Si3 N4 particles covered with a mixture of boric acid and urea. TEM observations of this nanocomposite revealed that the nanosized hexagonal BN ( h -BN) particles were homogeneously dispersed within Si3 N4 grains as well as at grain boundaries. As expected from the rules of composites, Young's modulus of both micro- and nanocomposites decreased with an increase in h -BN content, while the fracture strength of the nanocomposites prepared in this work was significantly improved, compared with the conventional microcomposites. 相似文献
14.
Young Sik Yoon Sang Woong Na Jaehyung Lee † Myeong-Woo Cho Eun-Sang Lee Won-Seung Cho 《Journal of the American Ceramic Society》2004,87(7):1374-1377
R -curve behavior of Si3 N4 –BN composites and monolithic Si3 N4 for comparison was investigated. Si3 N4 –BN composites showed a slowly rising R -curve behavior in contrast with a steep R -curve of monolithic Si3 N4 . BN platelets in the composites seem to decrease the crack bridging effects of rod-shaped Si3 N4 grains for small cracks, but enhanced the toughness for long cracks as they increased the crack bridging scale. Therefore, fracture toughness of the composites was relatively low for the small cracks, but it increased significantly to ∼8 MPa·m1/2 when the crack grew longer than 700 μm, becoming even higher than that of the monolithic Si3 N4 . 相似文献
15.
Corrosion of Si3 N4 under thin films of Na2 CO3 was investigated at 1000°C. Pure Si3 N4 and Si3 N4 with various additives were examined. Thermogravimetric analysis and morphology observations lead to the following detailed reaction mechanism: (I) decomposition of Na2 CO3 and formation of Na2 SiO3 , (II) rapid oxidation, and (III) formation of a protective silica layer below the silicate and a slowing of the reaction. For Si3 N4 with Y2 O3 additions, preferential attack of the grain-boundary phase occurred. The corrosion of pure Si and SiC was also studied for comparison to Si3 N4 . The corrosion mechanism generally applies to all three materials. Silicon reacted substantially faster than Si3 N4 and SiC. 相似文献
16.
Naoki Kondo Yoshikazu Suzuki Tatsuki Ohji 《Journal of the American Ceramic Society》2000,83(7):1816-1818
Silicon nitride–silicon carbide (Si3 N4 –SiC) nanocomposites were fabricated by a process involving reaction bonding followed by superplastic sinter-forging. The nanocomposites exhibited an anisotropic microstructure, in which rod-shaped, micrometer-sized Si3 N4 grains tended to align with their long axes along the material-flow direction. SiC particles, typically measuring several hundred nanometers, were located at the Si3 N4 grain boundaries, and nanosized particles were dispersed inside the Si3 N4 grains. A high bending strength of 1246 ± 119 MPa, as well as a high fracture toughness of 8.2 ± 0.9 MPa·m1/2 , was achieved when a stress was applied along the grain-alignment direction. 相似文献
17.
Chemical interaction within the system Si3 N4 -TiC was investigated in the present study by using thermodynamic calculations and kinetic analyses. The thermodynamic stabilities of such Si3 N4 -TiC composites as Si3 N4 -TiN-C and Si3 N4 -Ti(C,N)-C, and SiC-Ti(C,N) stability regions were defined and related to temperature and nitrogen partial pressures. Kinetic analyses were performed by constructing a relative weight-loss analysis of various Si3 N4 :TiC molar ratios reacted at temperatures from 1300° to 1750°C in an argon atmosphere. The reaction rates increased with the decreases in the Si3 N4 :TiC ratio and with increases in temperature. The reaction products consisted mainly of SiC and Ti(C,N) phases. The overall chemical interaction observed in the present study is attributable to chemical reactions between Si3 N4 and TiC and to the diffusion of carbon and nitrogen through the reaction layer after a dense reaction product layer had covered the titanium carbide. 相似文献
18.
Linus U. J. T. Ogbuji 《Journal of the American Ceramic Society》1992,75(11):2995-3000
The results of two-step oxidation experiments on chemically-vapor-deposited Si3 N4 and SiC at 1350°C show that a correlation exists between the presence of a Si2 N2 O interphase and the strong oxidation resistance of Si3 N4 . During normal oxidation, k p for SiC was 15 times higher than that for Si3 N4 , and the oxide scale on Si3 N4 was found by SEM and TEM to contain a prominent Si2 N2 O inner layer. However, when oxidized samples are annealed in Ar for 1.5 h at 1500°C and reoxidized at 1350°C as before, three things happen: the oxidation k p increases over 55-fold for Si3 N4 , and 3.5-fold for SiC; the Si3 N4 and SiC oxidize with nearly equal k p 's; and, most significant, the oxide scale on Si3 N4 is found to be lacking an inner Si2 N2 O layer. The implications of this correlation for the competing models of Si3 N4 oxidation are discussed. 相似文献
19.
Silicon Carbide Whisker Stability During Processing of Silicon Nitride Matrix Composites 总被引:1,自引:0,他引:1
Steven A. Bradley Keith R. Karasek Michael R. Martin Harry C. Yeh James L. Schienle 《Journal of the American Ceramic Society》1989,72(4):628-636
The effects of two different sources of SiC whiskers on the chemistry and microstructure of the SiC-whisker—Si3 N4 composites were evaluated using scanning transmission electron microscopy. Analyses were performed after presintering in N2 and after encapsulated hot isostatic pressing. Significant differences in the porosity, α- to β-Si3 N4 conversion, and whisker degradation were observed after presintering. It was also noted that whiskers containing surface iron impurities were converted to Si3 N4 during processing. Whiskers from the source having low surface iron exhibited little reaction. After hot isostatic pressing, some oxidation of the cleaner whiskers was observed. 相似文献
20.
Porous 2H-Silicon Carbide Ceramics Fabricated by Carbothermal Reaction between Silicon Nitride and Carbon 总被引:2,自引:0,他引:2
Jian-Feng Yang Guo-Jun Zhang Naoki Kondo Ji-Hong She Zhi-Hao Jin Tatsuki Ohji Shuzo Kanzaki 《Journal of the American Ceramic Society》2003,86(6):910-914
Porous SiC ceramics were synthesized by sintering pressed and pressed/CIPed powder compacts of α-Si3 N4 , carbon (Si3 N4 :C = 1:3 mol as ratio), and sintering aids, at 1600°C for few hours to achieve a reaction, and subsequently sintering at a temperature range of 1750°–1900°C, in an argon atmosphere. High porosities from 45%–65% were achieved by low shrinkage with large weight loss. Formation of pure 2H-SiC phase via a reaction between Si3 N4 and carbon can be demonstrated by X-ray diffractometry. The resultant porous SiC samples were characterized by SiC grain microstructures, pore-size distribution, and flexural strength. This method has the advantage of fabricating high-porous SiC ceramics with fine microstructure and good properties at a relatively low temperature. 相似文献