共查询到20条相似文献,搜索用时 15 毫秒
1.
Young-Wook Kim Mamoru Mitomo Toshiyuki Nishimura 《Journal of the American Ceramic Society》2002,85(4):1007-1009
Using AlN and RE2 O3 (RE = Y, Yb) as sintering additives, two different SiC ceramics with high strength at 1500°C were fabricated by hot-pressing and subsequent annealing under pressure. The ceramics had a self-reinforced microstructure consisting of elongated α-SiC grains and a grain-boundary glassy phase. High-temperature strength up to 1600°C was measured and compared with that of the SiC ceramics fabricated with AlN and Er2 O3 . SiC ceramics with AlN and Y2 O3 showed the best strength (∼630 MPa) at 1500°C, while SiC ceramics with AlN and Er2 O3 the best strength (∼550 MPa) at 1600°C. 相似文献
2.
Shuqi Guo Naoto Hirosaki Toshiyuki Nishimura Yoshinobu Yamamoto Mamoru Mitomo 《Journal of the American Ceramic Society》2003,86(11):1900-1905
The oxidation behavior and effect of oxidation on room-temperature flexural strength were investigated for hot-pressed Si3 N4 ceramics, with 3.33 and 12.51 wt% Lu2 O3 additives, exposed to air at 1400° and 1500°C for up to 200 h. Parabolic oxidation behavior was observed for both compositions. The oxidation products consisted of Lu2 Si2 O7 and SiO2 . The Lu2 Si2 O7 grew out of the surface silicate in preferred orientations. The morphology of oxidized surfaces was dependent on the amount of additive; Lu2 Si2 O7 grains in the 3.33 wt% composition appeared partially in a needlelike type, compared with a more equiaxed type exhibited in the 12.51 wt% case. The high resistance to oxidation shown for both compositions was attributed to the extensive amounts of crystalline, refractory secondary phases formed during the sintering process. Moreover, after 200 h of oxidation at 1400° and 1500°C, the strength retention displayed by the two compositions was 93%–95% and 85%–87%, respectively. The strength decrease was associated with the formation of new defects at the interface between the oxide layer and the Si3 N4 bulk. 相似文献
3.
The reactivity of AlN powder with water in supernatants obtained from centrifuged Si3 N4 and SiC slurries was studied by monitoring the pH versus time. Various Si3 N4 and SiC powders were used, which were fabricated by different production routes and had surfaces oxidized to different degrees. The reactivity of the AlN powder in the supernatants was found to depend strongly on the concentration of dissolved silica in these slurries relative to the surface area of the AlN powder in the slurry. The hydrolysis of AlN did not occur if the concentration of dissolved silica, with respect to the AlN powder surface, was high enough (1 mg SiO2 /(m2 AlN powder)) to form a layer of aluminosilicates on the AlN powder surface. This assumption was verified by measuring the pH of more concentrated (31 vol%) Si3 N4 and SiC suspensions also including 5 wt% of AlN powder (with respect to the solids). 相似文献
4.
Gas pressure sintering kinetics of silicon nitride powder coated with 10 wt% (9:1) Al2 O3 and TiO2 have been studied at 1850°C with a pressure schedule of 0.3 MPa in the first stage and 1 MPa in the second stage. The rates have been analyzed with a liquid-phase sintering model. Diffusion-controlled intermediate-stage kinetics have been observed. The role of second-step pressurization with nitrogen and argon has been determined by monitoring the kinetics. Pressurization at an earlier stage (∼90% relative density) reduces the densification rate but produces a denser material at the final stage. Although final density is greater, a porous surface layer forms on samples sintered with argon pressurization at the second stage. No such porous layer is formed in the case of pressurization with nitrogen. The mechanism of the intermediate-stage kinetics has been discussed with respect to the nature of the product analyzed by XRD after sintering. 相似文献
5.
Krishan L. Luthra 《Journal of the American Ceramic Society》1991,74(5):1095-1103
This study provides new perspectives on why the oxidation rates of silicon carbide and silicon nitride are lower than those of silicon and on the conditions under which gas bubbles can form on them. The effects on oxidation of various rate-limiting steps are evaluated by considering the partial pressure gradients of various species, such as O2 , CO, and N2 . Also calculated are the parabolic rate constants for the situations when the rates are controlled by oxygen and/or carbon monoxide (or nitrogen) diffusion. These considerations indicate that the oxidation of silicon carbide and silicon nitride should be mixed controlled, influenced both by an interface reaction and diffusion. 相似文献
6.
Young-Wook Kim Mamoru Mitomo Toshiyuki Nishimura 《Journal of the American Ceramic Society》2001,84(9):2060-2064
Fully dense SiC ceramics with high strength at high temperature were obtained by hot-pressing and subsequent annealing under pressure, with AlN and Er2 O3 as sintering additives. The ceramics had a self-reinforced microstructure consisting of elongated SiC grains and a grain-boundary glassy phase. The strength of these ceramics was ∼550 MPa at 1600°C, and the fracture toughness was ∼6 MPa·m1/2 at room temperature. The beneficial effect of the new additive composition on high-temperature strength might be attributable to the introduction of aluminum from the liquid composition into the SiC lattice, resulting in a refractive grain-boundary glassy phase. 相似文献
7.
Preparation of Silicon Carbide/Aluminum Nitride Ceramics Using Organometallic Precursors 总被引:1,自引:0,他引:1
Corinna L. Czekaj Michael L. J. Hackney William J. Hurley Jr. Leonard V. Interrante Gary A. Sigel Paul J. Schields Glen A. Slack 《Journal of the American Ceramic Society》1990,73(2):352-357
Solid solutions of 2H -SiC/AlN can be prepared at temperatures less than 1600°C by rapid pyrolysis ("hot drop") of mixtures of [(Me3 Si)0.80 ((CH2 =CH)MeSi)1.0 (MeHSi)0.35 ] n (VPS) or [MeHSiCH2 ] n (MPCS) with [R2 AlNH2 ]3 , where R=Et, i -Bu or simply by slow pyrolysis of the precursor mixture in the case of [Et2 AlNH2 ]3 . In contrast, slow pyrolysis of mixtures of VPS or MPCS with [ i -Bu2 AlNH2 ]3 yields a composite of 2 H -AlN and 3 C -SiC at 1600°C, which transforms into a single 2 H -SiC/AlN solid solution on heating to 2000°C. The influences of the nature of the precursor and processing conditions on the structure, composition, and purity of the SiC/AlN materials are discussed. 相似文献
8.
Yong S. Cheong Priya Mukundhan Henry H. Du Stephen P. Withrow 《Journal of the American Ceramic Society》2000,83(1):161-65
In the preceding paper, it was shown that aluminum ion implantation significantly improves the oxidation resistance of Si3 N4 ceramics under the influence of sodium. Not only is the oxidation rate reduced by up to an order of magnitude, the phase and morphological characteristics of the oxides grown on aluminum-implanted samples are improved as well. The role of aluminum in negating the detrimental effect of sodium on the oxidation resistance of Si3 N4 ceramics can be interpreted on the basis of network modification of the oxide layers by sodium and aluminum cations. The degree of improvement in the oxidation resistance does not, however, necessarily increase with the aluminum concentration. A simple quantitative analysis is presented which correlates the optimum aluminum implant concentration and the sodium content in the gas phase for the optimization of the oxidation resistance of Si3 N4 ceramics. 相似文献
9.
Volatility Diagrams for Silica, Silicon Nitride, and Silicon Carbide and Their Application to High-Temperature Decomposition and Oxidation 总被引:1,自引:0,他引:1
Volatility diagrams—isothermal plots showing the partial pressures of two gaseous species in equilibrium with the several condensed phases possible in a system—are discussed for the Si-O and Si-N systems, and extended to the Si-N-O and Si-C-O systems, in which the important ceramic constituents SiO2 , Si3 N4 , Si2 N2 O, and SiC appear as stable phases. Their use in understanding the passiveactive oxidation transitions for Si, Si3 N4 , and SiC are demonstrated. 相似文献
10.
Yong S. Cheong Priya Mukundhan Henry H. Du Stephen P. Withrow 《Journal of the American Ceramic Society》2000,83(1):154-60
Hot-isostatically-pressed, additive-free Si3 N4 ceramics were implanted with aluminum at multi-energies and multidoses to achieve uniform implant concentrations at 1, 5, and 10 at.% to a depth of about 200 nm. The oxidation behavior of unimplanted and aluminum-implanted Si3 N4 samples was investigated in 1 atm flowing oxygen entrained with 100 and 220 ppm NaNO3 vapor at 900–1100°C. Unimplanted Si3 N4 exhibits a rapid, linear oxidation rate with an apparent activation energy of about 70 kJ/mol, independent of the sodium content in the gas phase. Oxides formed on the unimplanted samples are rough and are populated with cracks and pores. In contrast, aluminum-implanted Si3 N4 shows a significantly reduced, parabolic oxidation rate with apparent activation energies in the range of 90–140 kJ/mol, depending on the sodium content as well as the implant concentration. The oxides formed on the implanted samples are glassy and mostly free from surface flaws. The alteration of the oxidation kinetics and mechanism of Si3 N4 in a sodium-containing environment by aluminum implantation is a consequence of the effective modification of the properties of the sodium silicates through aluminum incorporation. 相似文献
11.
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
12.
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
13.
Wieslaw A. Zdaniewski Cheryl A. Houser 《Journal of the American Ceramic Society》1989,72(11):2084-2087
Aluminum nitride and silicon carbide substrates were screen-printed with fritless gold and fired at 850°C in air. Interfacial diffusion zones up to 7 αm thick were observed, in which the concentrations of Au, Na impurities, and combined O varied together. Secondary ion mass and photoelectron spectroscopy revealed oxidized Al in the gold conductor supported by AIN. It is suggested that enhanced oxidation accompanies the diffusion of Au into the ceramics. 相似文献
14.
The oxygen content of silicon nitride with 1 mol% Y2 O3 —Nd2 O3 additive was measured after firing to determine the compositional change during gas-pressure sintering. Oxygen content decreases from 2.5 to 0.94 wt% during firing for 4 h at 1900°C and 10-MPa pressure in N2 . This decrease in oxygen results from the release of SiO gas generated by a thermaldecomposition reaction between Si3 N4 and SiO2 . The resultant sintered silicon nitride material contains less than 1 wt% oxygen. 相似文献
15.
Takayuki Nagano Hui Gu Kenji Kaneko Guo-Dong Zhan Mamoru Mitomo 《Journal of the American Ceramic Society》2001,84(9):2045-2050
Nanocrystalline β-SiC with additions of 7 wt% Al2 O3 , 2 wt% Y2 O3 , and 1 wt% CaO was subjected to tensile deformation to study its microstructural behavior under the dynamic process. The liquid-phase-sintered body had a relative density of >97% and an average grain size of 170 nm. Tension tests were conducted at initial strain rates ranging from 2 × 10−5 to 5 × 10−4 s−1 , in the temperature range 1973–2023 K, in both argon and N2 atmospheres. Although grain-boundary liquids formed by the additions vaporized concurrently with the decomposition of SiC and extensive grain growth, the maximum tensile elongation of 48% was achieved in argon. Annealing experiments under the same conditions revealed that vaporization and grain growth were both dependent on experimental time. Therefore, high strain rates suffered less from the hardening effect when cavitation damage was more severe. Testing in an N2 atmosphere brought about crystallization of the grain-boundary phase and prevented severe vaporization; however, fracture occurred at only 8% elongation. Grain-boundary sliding was still the dominant mechanism for deformation. 相似文献
16.
Xuguang Tong Jianbao Li Xiaozhan Yang Hong Lin Gangfeng Guo Mingsheng He 《Journal of the American Ceramic Society》2006,89(5):1730-1732
In this work, self-reinforced silicon nitrides with β-Si3 N4 seeds doped with Re2 O3 (Re=Yb, Lu) were investigated. Firstly, the two kinds of seeds were obtained by heating α-Si3 N4 powder with Yb2 O3 or Lu2 O3 , respectively. Then the self-reinforced silicon nitride ceramics were prepared by HP-sintering of α-Si3 N4 powder, Re2 O3 as additive, and the as-prepared seeds. Oxidation test was carried out at 1400°C in air for 100 h with thermogravimetry analysis (TGA) measurement. Mechanical properties, scanning electronic microscopy microstructures, and X-ray diffraction patterns were measured before and after oxidation. The results indicated that the introduction of the seeds doped with Re2 O3 (Re=Yb, Lu) could obviously increase the toughness and keep the room temperature and high-temperature strength of the ceramics at high values. After oxidation, the crystalline phase in grain boundary changed and the mechanical properties decreased. TGA showed a parabolic weight gain and the oxidation mechanism was discussed. 相似文献
17.
Yury G. Gogotsi Franz Porz Viktor P. Yaroshenko 《Journal of the American Ceramic Society》1992,75(8):2251-2259
The study examines the effect which the composition of hot-pressed electroconductive ceramics has on their structure, mechanical properties, and oxidation behavior, for ceramics of the type AIN–Al2 O3 –42 wt% TiN, differing in the AIN/Al2 O3 ratio. The results are physico-mechanical property data, including density, hardness, strength, fracture toughness, and wear resistance. A correlation was found between the wear resistance and fracture toughness. The analysis of oxidation products revealed the formation of α-Al2 O3 and rutile in the temperature range from 600° to 1100°C and aluminum titanate above 1200°C. The spallation of the oxide layer caused low oxidation resistance of Al2 O3 -rich composites above 1250°C. The oxidation of composites was compared with the oxidation of pure TiN. The relationship is discussed between material properties, composition, phases, and processing parameters. 相似文献
18.
The fracture behavior of Al2 O3 /SiC nanocomposites has been studied as a function of the SiC volume fraction and compared to that of the pure Al2 O3 matrix. A pronounced strengthening effect was only observed for materials with low SiC content (i.e., ≤10 vol%) although no evidence of concurrent toughening was found. Assessment of near-tip crack opening displacement (COD) could not experimentally substantiate significant occurrence of an elastic crack-bridging mechanism, in contrast with a recently proposed literature model. Quantitative fractography analysis indicated that transgranular crack propagation in Al2 O3 /SiC nanocomposites depends on the location of the SiC dispersoids within the matrix texture; the higher the fraction of transgranularly located dispersoids, the more transgranular the fracture mode. Experimental evidence of remarkably high residual stresses arising from thermal dilatation mismatch (upon cooling) between Al2 O3 and SiC phases were obtained by fluorescence and Raman spectroscopy. A strengthening mechanism is invoked which merely arises from residual stress through strengthening of Al2 O3 grain boundaries. 相似文献
19.
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
20.
Takayuki Narushima Takashi Goto Yasutaka Iguchi Toshio Hirai 《Journal of the American Ceramic Society》1991,74(10):2583-2586
Active oxidation behavior of chemically vapor-deposited silicon carbide in an Ar─O2 atmosphere at 0.1 MPa was examined in the temperature range between 1840 and 1923 K. The transition from active oxidation (mass loss) to passive oxidation (mass gain) was observed at certain distinct oxygen partial pressures ( P O 2 t ). The values of P O 2 t increased with increasing temperature and with decreasing total gas flow rates. This behavior was well explained by Wagner's model and thermodynamic calculations. Active oxidation rates ( k a ) increased with increasing O2 partial pressures and total gas flow rates. The rate-controlling step of the active oxidation was concluded to be O2 diffusion through the gaseous boundary layer. 相似文献