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1.
Geometrical Microstructural Development in Superplastic Silicon Nitride with Rod-Shaped Grains 总被引:1,自引:0,他引:1
Naoki Kondo Eiichi Sato Fumihiro Wakai 《Journal of the American Ceramic Society》1998,81(12):3221-3227
The three-dimensional microstructural development of silicon nitride ceramics that exhibit superplastic elongation (up to ɛ = 1.34) was analyzed using a stereological analysis method. According to the microstructural change from randomly oriented grains to aligned grains along the tensile direction, the average orientation angle between the tensile axis and the major axis of a grain decreased monotonously as the strain increased. The average grain aspect ratio remained almost constant up to ɛ = 0.88 and then started to increase. Based on the microstructural development, three different modes of the change in the grain configuration-i.e., grain rotation, grain elongation, and grain translation-were considered. It is suggested that the contributions of the three modes vary according to the microstructural development during the deformation. 相似文献
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Guo-Dong Zhan Mamoru Mitomo Young-Wook Kim 《Journal of the American Ceramic Society》1999,82(10):2924-2926
Fine-grained (<1 μm) silicon carbide ceramics with high strength were obtained by using ultrafine (∼90 nm) β-SiC starting powders and a seeding technique for microstructural control. The microstructures of the as-hot-pressed and annealed ceramics without α-SiC seeds consisted of fine, uniform, and equiaxed grains. In contrast, the annealed material with seeds had a uniform, anisotropic microstructure consisting of elongated grains, owing to the overgrowth of β-phase on α-seeds. The strength, the Weibull modulus, and the fracture toughness of fine-grained SiC ceramics increased with increasing grain size up to ∼1 μm. Such results suggested that a small amount of grain growth in the fine grained region (<1 μm) was beneficial for mechanical properties. The flexural strength and the fracture toughness of the annealed seeded materials were 835 MPa and 4.3 MPa·m1/2 , respectively. 相似文献
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Nitin P. Padture Christopher J. Evans Hockin H. K. Xu‡ Brian R. Lawn 《Journal of the American Ceramic Society》1995,78(1):215-217
The machinability of a heterogeneous silicon carbide with weak interphase boundaries, elongated grains, and high internal stresses is evaluated relative to a homogeneous control material with a well-bonded, equiaxed, and unstressed grain structure. Drilling and grinding rates for the silicon carbide are substantially enhanced by the microstructural heterogeneity—the weak boundaries enable easy grain-scale dislodgement in place of the more conventional macrofracture chipping mode of removal. At the same time, the residual machining damage in the machined surfaces is significantly less strength degrading in the heterogeneous material. Implications concerning the microstructural design of flaw-tolerant ceramics for enhanced machinability are considered. 相似文献
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Guo-Dong Zhan Mamoru Mitomo Hidehiko Tanaka Young-Wook Kim 《Journal of the American Ceramic Society》2000,83(6):1369-1374
The effect of annealing with and without applied pressure on the microstructural development and phase transformation was investigated in fine-grained β-SiC ceramics containing α-SiC seeds. Materials annealed without pressure had a microstructure consisting of elongated grains, while materials annealed with pressure showed a duplex microstructure consisting of small matrix grains and some of elongated grains. However, annealing with pressure (25 MPa) was found to greatly retard phase transformation from β→α polytypes and inhibit grain growth. This change in lattice parameter suggests that the retardation of phase transformation and grain growth might be attributed to a reduced mass transport rate, which is the result of Al being introduced into the SiC by the annealing pressure. 相似文献
5.
Peter A. Smith Helen M. Kerch rew G. Haerle Joseph Keller 《Journal of the American Ceramic Society》1996,79(10):2515-2526
The effect of solids loading, particle-size distribution, and suspension viscosity on the resultant microstructure of slipcast monolithic ceramics prepared from aqueous suspensions of alumina and silicon carbide was studied. Unimodal alumina suspensions (average particle size = 0.6 μm) were prepared at 35, 37, and 42 vol%. Silicon carbide suspensions (average particle size = 0.7 μm) were produced with different quantities of dispersant at 37 vol%. Similarly, aqueous alumina suspensions of 42 and 50 vol% were produced with a bimodal particle-size distribution. The slip-cast microstructures were characterized by mercury porosimetry and small-angle neutron scattering, which provided pore size (distribution), pore fraction, and pore morphology. Essentially, the combination of these techniques deciphered packing differences obtained in the cake microstructures. For the alumina cakes produced from the 35,37, and 42 vol% suspensions, the individual characterization techniques, mercury intrusion, and the neutron scattering measurements showed that the cake microstructures were similar in pore size and quantity. However, comparison of the techniques and their assumptions showed differences in the pore shape. Mercury porosimetry and neutron scattering showed bimodal porosity for the cake produced from a mixture of 85% 6-μm particles and 15% 0.6-μm particles. Pore volume fraction and pore size increases were correlated with increased viscosity in the silicon carbide suspensions. In addition, the silicon carbide cake microstructures were measured, and homogeneity was evaluated as a function of position in the cast. 相似文献
6.
Ralph F. Jr. Krause Sheldon M. Wiederhorn Chien-Wei Li 《Journal of the American Ceramic Society》2001,84(10):2394-2400
The tensile creep behavior of a gas-pressure-sintered silicon nitride containing silicon carbide was characterized at temperatures between 1375° and 1450°C with applied stresses between 50 and 250 MPa. Individual specimens were tested at fixed temperatures and applied loads. Each specimen was pin-loaded within the hot zone of a split-tube furnace through silicon carbide rods connected outside the furnace to a pneumatic cylinder. The gauge length was measured by laser extensometry, using gauge markers attached to the specimen. Secondary creep rates ranged from 0.54 to 270 Gs−1, and the creep tests lasted from 6.7 to 1005 h. Exponential functions of stress and temperature were fitted to represent the secondary creep rate and the creep lifetime. This material was found to be more creep resistant than two other silicon nitride ceramics that had been characterized earlier by the same method of measurement as viable candidates for high-temperature service. 相似文献
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Charles A. Lewinsohn Lucille A. Giannuzzi Charles E. Bakis Richard E. Tressler 《Journal of the American Ceramic Society》1999,82(2):407-413
The creep behavior of three types of silicon carbide fibers that have been fabricated via chemical vapor deposition is described. The fibers exhibit only primary creep over the range of conditions studied (1200°–1400°C, 190–500 MPa). A transmission electron microscopy study of the microstructural development that is induced by the creep deformation of SCS-6 silicon carbide fibers at 1400°C is presented. Significant grain growth occurs in all silicon carbide regions of the fiber during creep, in contrast to the reasonably stable microstructure that is observed after annealing at the same temperature and time. 相似文献
11.
Creep and Microstructural Evolution at High Temperature of Liquid-Phase-Sintered Silicon Carbide 总被引:1,自引:0,他引:1
Juan J. Meléndez-Martínez Miguel Castillo-Rodríguez Arturo Domínguez-Rodríguez Angel L. Ortiz Fernando Guiberteau 《Journal of the American Ceramic Society》2007,90(1):163-169
The compressive creep characteristics at 1625°C of liquid-phase-sintered silicon carbide ceramics containing 5 and 15 wt% of crystalline Y3 Al5 O12 (YAG) as the secondary phase were studied. In the two cases, strains between 10% and 15% were reached without failure. The creep behavior was characterized by a stress exponent n ≈2, and the proportion of secondary phase was related to the creep resistance of the materials. The microstructural evolution during creep consisted firstly in the re-distribution of the secondary phase, probably as a consequence of its viscous flow at the creep conditions, and secondly an extensive nucleation and growth of cavities, which was more important for the highest YAG content. The latter reflects the carbothermal reduction that the secondary phase undergoes during creep. 相似文献
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At high temperatures in clean oxidizing environments, SiC forms a very protective SiO2 film, but, in environments containing low levels of gaseous alkali salt contaminants or where condensed salts may deposit on the surface, the resistance of the film is significantly reduced. Oxidation kinetics of SiC were measured by continuous thermogravimetric analysis in a controlled environment containing CO2 , H2 O, and O2 plus low levels of potassium-containing salts. Potassium was found to be incorporated into the SiO2 scale and to significantly change its transport properties and its morphology. The rate of scale formation was found to increase directly in proportion to K in the scale. A change in mechanism was observed when water vapor was added to the reacting gas stream. 相似文献
14.
Oxidation of Silicon, Silicon Carbide, and Silicon Nitride in Gases Containing Oxygen and Chlorine 总被引:1,自引:0,他引:1
PeiPei Hsu Sikyin Ip Chan Park Michael J. McNallan 《Journal of the American Ceramic Society》1993,76(6):1621-1623
Chlorine contamination accelerates the oxidation of silicon-based ceramics through the formation of volatile silicon chloride or silicon oxychloride species which degrade the protective character of the SiO2 film. Accelerated attack may occur by active corrosion or formation of bubbles in the oxide layer. Si3 N4 is much more resistant to this attack than either silicon or SiC. This resistance may be related to the presence of a thin silicon oxynitride layer below the SiO2 scale which forms on Si3 N4 . 相似文献
15.
Silicon nitride (Si3 N4 ) and SiAlONs can be self-toughened through the growth of elongated β-Si3 N4 /β-SiAlON grains in sintering. α-SiAlONs usually retain an equiaxed grain morphology and have a higher hardness but lower toughness than β-SiAlONs. The present work has demonstrated that elongated alpha-SiAlON grains can also be developed through pressureless sintering. alpha-SiAlONs with high-aspect-ratio grains in the calcium SiAlON system have exhibited significant grain debonding and pull-out effects during fracture, which offers promise for in-situ -toughened α-SiAlON ceramics. 相似文献
16.
RACHMAN CHAIM ARTHUR H. HEUER R.T. CHEN 《Journal of the American Ceramic Society》1988,71(11):960-969
Several continuous SiC and SiC/N-based ceramic fibers prepared from different polymer precursors have been characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), and high-resolution electron microscopy (HREM). Methods to prepare longitudinal as well as cross-sectional thin specimens from brittle ceramic fibers were developed to facilitate HREM and EELS studies. Lattice images clearly showed nanometer-sized crystallites, as well as amorphous regions. Microchemical analysis using EELS permitted study of the form and distribution of the various chemical species within the fibers. 相似文献
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Tyrone Mitchell Jr. † ‡ Lutgard C. De Jonghe † ‡ Warren J. MoberlyChan Robert O. Ritchie† ‡ 《Journal of the American Ceramic Society》1995,78(1):97-103
α-silicon carbide platelet/β-silicon carbide composites have been produced in which the individual platelets were coated with an aluminum oxide layer. Hot-pressed composites showed a fracture toughness as high as 7.2 MPa·m1/2 . The experiments indicated that the significant increase in fracture toughness is mainly the result of crack deflection and accompanying platelet pullout. The coating on the platelets also served to prevent the platelets from acting as nucleation sites for the α- to β-phase transformation, so that the advantageous microstructure remains preserved during high-temperature processing. 相似文献
18.
Judy Schneider Koushik Biswas Georg Rixecker Fritz Aldinger 《Journal of the American Ceramic Society》2003,86(3):501-507
The knowledge of the microstructural evolution during exposure to high temperatures is important to understanding the mechanisms responsible for the creep resistance of silicon carbide (SiC) ceramics. This includes not only the phase transformation of the SiC grains, but also the phase transformations of the oxynitride grain-boundary phases. For this study, a series of SiC specimens were prepared with varying molar ratios of AlN-Y2 O3 additives. Increased creep resistance was observed in specimens with an additive system containing a 2:3 molar ratio or 60 mol% Y2 O3 . A continuous oxide layer of Y2 Si2 O7 formed at the surface during elevated temperature testing in air. No blistering or cracking was observed in this oxide coating. Further increase of the creep resistance was achieved by a post-sintering nitrogen anneal. 相似文献
19.
碳化硅陶瓷以其优异的抗热震、耐高温、抗氧化和耐化学腐蚀等特性而广泛地应用于石油、化学。汽车、机械和宇航等工业领域中,井日益引起人们的重视。本文对各种SIC陶瓷的制备方法、性能特点及其应用现状进行了综合评述。 相似文献
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本文主要概述了高纯度SiC粉体、烧结体的制造方法及其制品,同时也涉及到了超高纯度SiC单晶的制造和应用。SiC材料纯度不仅与电、电子的特性密切相关,而且与机械、热、光学的特性密切相关,所以利用其优异的耐热性、强度、硬度、耐磨损性、抗化学药剂性、体积电阻系数等特性,对工业的发展起到了巨大作用,特别是在半导体产业方面,迅速扩大了使用SiC基板的产品市场。 相似文献