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1.
An indentation method for measuring shar strength in brittle matrix composites was applied to SiC-fiber/Si3 N4 -matrix samples. Three methods were used to manufacture the composites: reaction bonding of a Si/SiC preform, hot-pressing, and nitrogen-overpressure sintering. An indentation technique developed by Marshall for thin specimens was used to measure the shear strength of the interface and the interfacial friction stresses. This was done by inverting the sample after the initial push through and retesting the pushed fibers. SEM observations showed that the shear strength was determined by the degree of reaction between the fiber and the matrix unless the fiber was pushed out of its (well-bonded) sheath. 相似文献
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3.
Michael J. Hoffmann Alwin Nagel Peter Greil Günter Petzow 《Journal of the American Ceramic Society》1989,72(5):765-769
Si3 N4 composite materials containing up to 20 vol% SiC whiskers were slip cast and pressureless sintered at 1820°C and 0.13 MPa of N2 . Viscosimetry showed no influence of whisker loading on the rheology of the highly concentrated aqueous slips up to 15 vol% whiskers. During casting the whiskers were preferentially aligned parallel to the mold surfaces. Depending on the whisker loading, green densities of 0.64 to 0.69 fractional density could be achieved. Strong anisotropic shrinkage occurred during sintering with a maximum linear shrinkage of 21% perpendicular but only 7% parallel to the whisker plane. With increasing whisker content from 0 to 20 vol% sintered densities decreased from 0.98 to 0.88, respectively. 相似文献
4.
Branko Matovic Georg Rixecker Fritz Aldinger 《Journal of the American Ceramic Society》2004,87(4):546-549
This paper deals with the densification and phase transformation during pressureless sintering of Si3 N4 with LiYO2 as the sintering additive. The dilatometric shrinkage data show that the first Li2 O- rich liquid forms as low as 1250°C, resulting in a significant reduction of sintering temperature. On sintering at 1500°C the bulk density increases to more than 90% of the theoretical density with only minor phase transformation from α-Si3 N4 to β-Si3 N4 taking place. At 1600°C the secondary phase has been completely converted into a glassy phase and total conversion of α-Si3 N4 to β-Si3 N4 takes place. The grain growth is anisotropic, leading to a microstructure which has potential for enhanced fracture toughness. Li2 O evaporates during sintering. Thus, the liquid phase is transient and the final material might have promising mechanical properties as well as promising high-temperature properties despite the low sintering temperature. The results show that the Li2 O−Y2 O3 system can provide very effective low-temperature sintering additives for silicon nitride. 相似文献
5.
Composite ceramic materials based on Si3 N4 and ZrO2 stabilized by 3 mol% Y2 O3 have been formed using aluminum isopropoxide as a precursor for the Al2 O3 sintering aid. Densification was carred out by hot-pressing at temperatures in the range 1650° to 1800°C, and the resulting micro-structures were related to mechanical properties as well as to oxidation behavior at 1200°C. Densification at the higher temperatures resulted in a fibrous morphology of the Si3 N4 matrix with consequent high room-temperature toughness and strength. Decomposition of the ZrO2 grains below the oxidized surface during oxidation introduced radial stresses in the subscalar region, and from the oxidation experiments it is suggested that the ZrO2 incorporated some N during densification. 相似文献
6.
Fumiyasu Oba Kazuyoshi Tatsumi Isao Tanaka Hirohiko Adachi 《Journal of the American Ceramic Society》2002,85(1):97-100
First-principles calculations have been conducted to investigate impurities in cubic Si3 N4 and Ge3 N4 . Impurity species suitable for n - and p -type doping are suggested, in terms of the formation and ionization energies. The suggested species are P and O as n -type dopants and Al as a p -type dopant for c -Si3 N4 , and Sb and O as n -type dopants and Al as a p -type dopant for c -Ge3 N4 . The dependence of the formation energies on the chemical potentials indicates that a proper choice of growth conditions is mandatory for suppressing the incorporation of these impurities into anti and interstitial sites, where the impurities can be charged to compensate carriers. 相似文献
7.
Using a recently developed first-principles supercell method that includes the electron and core-hole interaction, the XANES/ELNES spectra of Si- L 2,3 , Si- K , and N- K edges in α-Si3 N4 , β-Si3 N4 , spinel c -Si3 N4 , and Si2 N2 O were calculated and compared. The difference in total energies between the initial ground state and the final core-hole state provides the transition energy. The calculated spectra are found to be in good agreement with the experimental measurements on β-Si3 N4 and c -Si3 N4 . The differences in the XANES/ELNES spectra for the same element in different crystals are explained in terms of differences in local bonding. The use of orbital-decomposed local density of states to explain the measured spectra is shown to be inadequate. These results reaffirm the importance of including the core-hole effect in any XANES/ELNES spectral calculation. 相似文献
8.
Hui Gu Rowland M. Cannon Hans J. Seifert Michael J. Hoffmann Isao Tanaka 《Journal of the American Ceramic Society》2002,85(1):25-32
The nitrogen solubility in the SiO2 -rich liquid in the metastable binary SiO2 -Si3 N4 system has been determined by analytical TEM to be 1%–4% of N/(O + N) at 1973–2223 K. Analysis of the near edge structure of the electron energy loss peak indicates that nitrogen is incorporated into the silicate network rather than being present as molecular N2 . A regular solution model with a positive enthalpy of mixing for the liquid was used to match the data for the metastable solubility of N in the presence of crystalline Si3 N4 and to adjust the computed phase diagram. The solubility of Si3 N4 in fused SiO2 is far less than reported in liquid silicates also containing Al, Mg, and/or Y. Apparently, these cations act as modifiers that break anion bridges in the silicate network and, thereby, allow further incorporation of Si3 N4 without prohibitive amounts of network cross-linking. Finally, indications emerged regarding the diffuse nature of the Si3 N4 -SiO2 interface that leads to amorphous regions of higher N content. 相似文献
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Elizabeth J. Opila R. Craig Robinson Dennis S. Fox Richard A. Wenglarz Mattison K. Ferber 《Journal of the American Ceramic Society》2003,86(8):1262-1271
Two commercially available additive-containing silicon nitride materials were exposed in four environments which ranged in severity from dry oxygen at 1 atm pressure, and low gas velocity, to an actual turbine engine. Oxidation and volatilization kinetics were monitored at temperatures ranging from 1066° to 1400°C. The main purpose of this paper is to examine the surface oxide morphology resulting from the exposures. It was found that the material surface was enriched in rare-earth silicate phases in combustion environments when compared with the oxides formed on materials exposed in dry oxygen. However, the in situ formation of rare-earth disilicate phases offered little additional protection from the volatilization of silica observed in combustion environments. It was concluded that externally applied environmental barrier coatings are needed to protect additive-containing silicon nitride materials from volatilization reactions in combustion environments. 相似文献
10.
Shuichi Kawano Junichi Takahashi Shiro Shimada 《Journal of the American Ceramic Society》2003,86(4):701-705
TiN-coated Si3 N4 particles were prepared by depositing TiO2 on the Si3 N4 surfaces from Ti(O- i -C3 H7 )4 solution, the TiO2 being formed by controlled hydrolysis, then subsequently nitrided with NH3 gas. A homogeneous TiO2 coating was achieved by heating a Si3 N4 suspension containing 1.0 vol% H2 O with the precursor at 40°C. Nitridation successfully produced Si3 N4 particles coated with 10–20 nm TiN particles. Spark plasma sintering of these TiN/Si3 N4 particles at 1600°C yielded composite ceramics with a relative density of 96% at 25 vol% TiN and an electrical resistivity of 10−3 Ω·cm in compositions of 17.5 and 25 vol% TiN/Si3 N4 , making these ceramics suitable for electric discharge machining. 相似文献
11.
Crack-Healing Behavior of Si3 N4 /SiC Ceramics under Cyclic Stress and Resultant Fatigue Strength at the Healing Temperature 总被引:1,自引:0,他引:1
Kotoji Ando Koji Takahashi Shin Nakayama Shinji Saito 《Journal of the American Ceramic Society》2002,85(9):2268-2272
Si3 N4 /SiC composite ceramics were sintered and subjected to three-point bending. A semi-elliptical surface crack of 100 μm surface length was made on each specimen. The crack-healing behavior under cyclic stress of 5 Hz, and resultant cyclic fatigue strengths at healing temperatures of 1100° and 1200°C, were systematically investigated. The main conclusions are as follows: (1) Si3 N4 /SiC composite ceramics have an excellent ability to heal a crack at 1100° and 1200°C. (2) This sample could heal a crack even under cyclic stress at a frequency of 5 Hz. (3) The crack-healed sample exhibited quite high cyclic fatigue strength at each crack-healing temperature, 1100° and 1200°C. 相似文献
12.
Developing the texture of ceramics is one of the effective ways for improving properties. Although the magnetic susceptibility of nonmagnetic materials is very small, there is a possibility to control the crystal orientation using a high magnetic field due to a magnetic anisotropy. In this study, Si3 N4 ceramics were manufactured by a slip-casting process under high magnetic field and pressureless sintering. The texture of Si3 N4 ceramics was studied using X-ray diffraction and scanning electron micrographs of polished and plasma-etched specimens. It has been found that most of the a,b -axes texture of β-Si3 N4 grains aligned to the magnetic field direction. 相似文献
13.
Shuqi Guo Naoto Hirosaki Yoshinobu Yamamoto Toshiyuki Nishimura Mamoru Mitomo 《Journal of the American Ceramic Society》2002,85(6):1607-1609
The effect of oxidation exposure on room-temperature flexural strength was examined in 3.33- and 12.51-wt%-Lu2 O3 -containing hot-pressed Si3 N4 ceramics exposed to air at 1500°C for up to 1000 h. After oxidation exposure, the room-temperature strength of the ceramics was degraded, and strength retention decreased with time at temperature, dependent on the amount of additive. The retention in room-temperature strength displayed by the two compositions after 1000 h of oxidation exposure was 75%–80%. The degradation in strength was attributed to the formation of new defects at and/or near the interface between the oxide layer and the Si3 N4 bulk during oxidation exposure. 相似文献
14.
Hideki Hyuga Mark I. Jones Kiyoshi Hirao Yukihiko Yamauchi 《Journal of the American Ceramic Society》2004,87(4):699-702
The tribological behavior of monolithic Si3 N4 and a Si3 N4 /carbon fiber composite has been assessed under high load and low speeds in an aqueous environment. The results showed that the friction coefficient of the Si3 N4 was not significantly reduced when compared with dry sliding, and this was attributed to the failure to maintain a lubricating layer between the solid–solid surfaces. In the case of the composite, the initial high friction coefficient was reduced shortly after the beginning of the wear test and maintained a low value (about 0.03) throughout. This was attributed to the solid lubricating effect of the composite resulting in lower stress at the contact asperities, preventing the removal of the lubricating layer. 相似文献
15.
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
16.
John E. Ritter Karl Jakus Micheal H. Godin Robert Ruh 《Journal of the American Ceramic Society》1992,75(7):1760-1766
Crack growth behavior under creep conditions was studied in SiC-whisker-reinforced mullite and silicon nitride. Tests of four-point bend specimens with indentation cracks were periodically interrupted to observe the creep behavior. At each interruption the bulk creep strain of the specimen, the growth of the indentation cracks, and the nucleation and growth of creep-induced cracks were measured. A strong linear correlation was observed in both materials between the crack growth rate and the creep strain rate. For a given strain rate, cracks in the silicon nitride composite propagated at velocities about an order of magnitude greater than those in the mullite composite. On the other hand, for similar nominal stresses, creep rates in the silicon nitride composites were about an order of magnitude less than with the mullite composite. 相似文献
17.
Ramakrishna T. Bhatt 《Journal of the American Ceramic Society》1992,75(2):406-412
The room-temperature mechanical properties of a SiC-fiberreinforced reaction-bonded silicon nitride composite were measured after 100 h treatment in nitrogen and oxygen environments to 1400°C. The composite heat-treated in nitrogen to 1400°C showed no appreciable loss in properties. In contrast, composites heat-treated in oxygen from 600° to 1000°C retained ∼65% and 35% of the matrix fracture and ultimate strength, respectively, of the as-fabricated composites, and those heat-treated from 1200° to 1400°C retained greater than 90% and 65% of the matrix fracture and ultimate strength, respectively, of the as-fabricated composites. For all nitrogen and oxygen treatments, the composite displayed strain capability beyond the matrix fracture strength. Oxidation of the fiber surface coating, which caused degradation of bond between the fiber and matrix and reduction in fiber strength, appears to be the dominant mechanism for property degradation of the composites oxidized from 600° to 1000°C. Formation of a protective silica coating at external surfaces of the composites at and above 1200°C reduced oxidation of the fiber coating and hence degrading effects of oxidation on their properties. 相似文献
18.
Edward S. Fisher Murli H. Manghnani Ji-Fan Wang Jules L. Routbort 《Journal of the American Ceramic Society》1992,75(4):908-914
A study of the elastic moduli of Al2 O3 and Si3 N4 ceramics reinforced with 0 to 25 wt% SiC whiskers has been performed. The Young's moduli, shear moduli, and longitudinal modulus are compared with calculated predictions for aligned fiber composites by Hill and Hashin and Rosen, and for fibers randomly oriented in three dimensions by Christensen and Waal. The measured values are in excellent quantitative agreement with those derived for the random orientation of the SiC whiskers. 相似文献
19.
The effects of heat treatment in Ar-O2 and H2 -H2 O atmospheres on the flexural strength of hot isostatically pressed Si3 N4 were investigated. Increases in room-temperature strength, to values significantly above that of the aspolished material, were observed when the Si3 N4 was exposed at 1400°C to (1) H2 with water vapor pressure ( P H2O ) greater than 1 × 10−4 MPa or (2) Ar with oxygen partial pressure ( P O2 ) of between 7 × 10−6 and 1.5 × 10−5 MPa. However, the strength of the material was degraded when the P H2O in H2 was lower than 1 × 10−4 MPa, and essentially unaffected when the P O2 in Ar was higher than 1.5 × 10−5 MPa. We suggest that the observed strength increases are the result of strength-limiting surface flaws being healed by a Y2 Si2 O7 layer formed during exposure. 相似文献
20.
We investigated the effects of a chemically-vapor-deposited mullite coating (∼100 nm) on the oxidation resistance of sintered Si3 N4 in air and steam environments. The coating was sacrificially incorporated into the thermally grown oxide (TGO) on Si3 N4 during isothermal oxidation in air at 1400°C, leading to significantly reduced TGO growth as well as markedly improved TGO morphology. This improvement can be attributed to the refractory and viscous nature of the SiO2 -Al2 O3 system, compared with SiO2 , when under the influence of alkali and/or alkaline-earth fluxing elements. However, the mullite coating had little effect on the stability of the ceramic in the steam environment at 1200°C, due likely to high activity of SiO2 in mullite. 相似文献