共查询到20条相似文献,搜索用时 10 毫秒
1.
Mikio Fukuhara 《Journal of the American Ceramic Society》1989,72(2):236-242
The effect of Al2 O3 and (Ti or Si)C additions on various properties of a (Y)TZP (yttria-stabilized tetragonal zirconia polycrystal)–Al2 O3 –(Ti or Si)C ternary composite ceramic were investigated for developing a zirconia-based ceramic stronger than SiC at high temperatures. Adding Al2 O3 to (Y)TZP improved transverse rupture strength and hardness but decreased fracture toughness. This binary composite ceramic revealed a rapid loss of strength with increasing temperature. Adding TiC to the binary ceramic suppressed the decrease in strength at temperatures above 1573 K. The residual tensile stress induced by the differential thermal expansion between ZrO2 and TiC therefore must have inhibited the t - → m -ZrO2 martensitic transformation. It was concluded that a continuous skeleton of TiC prevented grain-boundary sliding between ZrO2 and Al2 O3 . In contrast, for the ternary material containing β-SiC in place of TiC, the strength decreased substantially with increasing temperature because of incomplete formation of the SiC skeleton. 相似文献
2.
Jonathan D. French Helcn M. Chan Martin P. Harmer Gary A. Miller 《Journal of the American Ceramic Society》1992,75(2):418-423
Composites of Al2 O3 (A) and cubic ZrO2 (Z) (8 mol% Y2 O3 ) (with c -ZrO2 volume fractions ranging from O to 1) were fabricated by pressureless sintering of mechanically mixed powders. The microstructures of the AZ composites were duplex, with the grains of both phases exhibiting similar size. Room-temperature mechanical properties including Young's modulus (determined from elastic wave velocity measurements), strength and toughness (by indentation-strength-in-bending), and Vickers microhardness were evaluated for the full range of compositions. All properties exhibited a linear decrease with increasing c -ZrO2 content, and no R -curve behavior was seen in any of the composite compositions. Fracture morphology, observed from cracks emanating from microhardness indentations, changed from essentially intergranular for the tougher Al2 O3 to transgranular for c -ZrO2 , with AZ composites exhibiting mixed morphology. 相似文献
3.
Jung-In Yang Sahn Nahm Chang-Hack Choi Hwack-Joo Lee Hyun-Min Park 《Journal of the American Ceramic Society》2002,85(1):165-168
The effect of ZrO2 on crystallographic order, microstructure, and microwave dielectric properties of Ba(Zn1/3 Ta2/3 )O3 (BZT) ceramics was investigated. A small amount of ZrO2 disturbed the 1:2 cation ordering. The average grain size of the BZT significantly increased with the addition of ZrO2 , which was attributed to liquid-phase formation. The relative density increased with the addition of a small amount of ZrO2 , but it decreased when the ZrO2 content was increased. Variation of the dielectric constant with ZrO2 addition ranged between 27 and 30, and the temperature coefficient of resonant frequency increased abruptly as the ZrO2 amount exceeded 2.0 mol%. The Q value of the BZT significantly improved with the addition of ZrO2 , which could be explained by the increased relative density and grain size. The maximum Q × f value achieved in this investigation was ∼164 000 GHz for the BZT with 2.0 mol% ZrO2 sintered at 1550°C for 10 h. 相似文献
4.
Ana E. Bohé Julio Andrade-Gamboa Daniel M. Pasquevich Alfredo J. Tolley Jorge L. Pelegrina 《Journal of the American Ceramic Society》2000,83(4):755-760
The microstructure of ZrO2 fine particles produced by a novel synthesis method at 450° and 950°C has been studied. The fundamentals of the synthesis method, which involves both chemical and diffusion phenomena, are presented. The method is based on mass transport through the gaseous phase between metallic zirconium and Fe2 O3 powder. The mass-transporting chemical species are zirconium and iron chlorides. This article focuses on the microstructure and structure of ZrO2 particles formed by the reaction between gaseous ZrCl4 and solid Fe2 O3 , which is a relevant reaction step that occurs during the synthesis process. The resulting ZrO2 crystals grown on Fe2 O3 particles have been analyzed using transmission electron microscopy. Microstructural characterization has been complemented by X-ray diffractometry analysis. Tetragonal-ZrO2 is produced at 450°C and monoclinic-ZrO2 single crystals are produced at 950°C. 相似文献
5.
D. Doni Jayaseelan N. Kondo D. Amutha Rani S. Ueno T. Ohji S. Kanzaki 《Journal of the American Ceramic Society》2002,85(11):2870-2872
The pulse electric current sintering technique (PECS) was demonstrated to be effective in rapid densification of fine-grained Al2 O3 /3Y-ZrO2 using available commercial powders. The composites attained full densification (>99% of TD) at 1450°C in less than 5 min. The composites sintered at a high heating rate had a fine microstructure. The incorporation of 3 vol% 3Y-ZrO2 substantially increased the average fracture strength and the toughness of alumina to as high as 827 MPa and 6.1 MPa·m1/2 , respectively. A variation in the heating rate during the PECS process influenced grain size, microstructure, and strength, though there was little or no variation in the fracture toughness. 相似文献
6.
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
7.
Siegfried Skirl Ralph Krause Sheldon M. Wiederhorn Jürgen Rödel 《Journal of the American Ceramic Society》2001,84(9):2034-2040
Composites with microstructures of interpenetrating networks were manufactured by gas pressure infiltration of Ni3 Al into porous preforms of aluminum oxide. Composites with Ni3 Al contents of between 15% and 30% by volume were made and evaluated mechanically at temperatures between room temperature and 1000°C. The fracture strength, the fracture toughness, Young's modulus, and the thermal expansion coefficient were measured for each composite and test condition and were correlated with the microstructures of the composites. Composites with low Ni3 Al contents had strengths below 400 MPa, presumably due to microcracking along the interface between the Ni3 Al and the Al2 O3 . The composite with the highest content of Ni3 Al, 30 vol%, had a mean fracture strength of 675 ± 16 MPa, a Weibull modulus of 23.9, and a room-temperature toughness of 9.2 ± 0.5 MPa·m1/2 . 相似文献
8.
Atsushi Kitaoka Ken Hirota Masaru Yoshinaka Yoshinari Miyamoto Osamu Yamaguchi 《Journal of the American Ceramic Society》2000,83(5):1311-1313
NiAl/10-mol%-ZrO2 (3Y) composites of almost full density have been fabricated via spark plasma sintering (SPS) for 10 min at 1300°C and 30 MPa. The former intermetallic compound, which contains a trace amount of Al2 O3 , has been prepared via self-propagating high-temperature synthesis. The composite microstructures are such that tetragonal ZrO2 (∼0.2 μm) and Al2 O3 (∼0.5 μm) particles are located at the grain boundaries of the NiAl (∼46 μm) matrix. Improved mechanical properties are obtained: the fracture toughness and bending strength are 8.8 MPa·m1/2 and 1045 MPa, respectively, and high strength (>800 MPa) can be retained up to 800°C. 相似文献
9.
Koji Tsukuma 《Journal of the American Ceramic Society》2000,83(12):3219-3221
Composites of β-Ce2 O3 ·11Al2 O3 and tetragonal ZrO2 were fabricated by a reductive atmosphere sintering of mixed powders of CeO2 , ZrO2 (2 mol% Y2 O3 ), and Al2 O3 . The composites had microstructures composed of elongated grains of β-Ce2 O3 ·11Al2 O3 in a Y-TZP matrix. The β-Ce2 O3 ·11Al2 O3 decomposed to α-Al2 O3 and CeO2 by annealing at 1500°C for 1 h in oxygen. The elongated single grain of β-Ce2 O3 ·11Al2 O3 divided into several grains of α-Al2 O3 and ZrO2 doped with Y2 O3 and CeO2 . High-temperature bending strength of the oxygen-annealed α-Al2 O3 composite was comparable to the β-Ce2 O3 ·11Al2 O3 composite before annealing. 相似文献
10.
Hae-Won Kim Young-Hag Koh Hyoun-Ee Kim 《Journal of the American Ceramic Society》2000,83(11):2863-2865
The densification behavior and mechanical properties of B4 C hot-pressed at 2000°C for 1 h with additions of Al2 O3 up to 10 vol% were investigated. Sinterability was greatly improved by the addition of a small amount of Al2 O3 . The improvement was attributed to the enhanced mobility of elements through the Al2 O3 near the melting temperature or a reaction product formed at the grain boundaries. As a result of this improvement in the density, mechanical properties, such as hardness, elastic modulus, strength, and fracture toughness, increased remarkably. However, when the amount of Al2 O3 exceeded 5 vol%, the level of improvement in the mechanical properties, except for fracture toughness, was reduced presumably because of the high thermal mismatch between B4 C and Al2 O3 . 相似文献
11.
The cubic ( c -ZrO2 ) and tetragonal zirconia ( t -ZrO2 ) phase stability regions in the system ZrO2 –Y2 O3 –Ta2 O5 were delineated. The c -ZrO2 solid solutions are formed with the fluorite structure. The t -ZrO2 solid solutions having a c/a axial ratio (tetragonality) smaller than 1.0203 display high fracture toughness (5 to 14 MPa · m1/2 ), and their instability/transformability to monoclinic zirconia ( m -ZrO2 ) increases with increasing tetragonality. On the other hand, the t -ZrO2 solid solutions stabilized at room temperature with tetragonality greater than 1.0203 have low toughness values (2 to 5 MPa · m1/2 ), and their transformability is not related to the tetragonality. 相似文献
12.
Yoshihiko Takano Masahiro Hachiya† Masaru Yoshinaka† Ken Hirota Osamu Yamaguchi 《Journal of the American Ceramic Society》2000,83(2):448-450
CrN powder consisting of granular particles of ∼3 μm has been prepared by self-propagating high-temperature synthesis under a nitrogen pressure of 12 MPa using Cr metal. Dense pure CrN ceramics and CrN/ZrO2 (2Y) composites in the CrN-rich region have been fabricated by hot isostatic pressing for 2 h at 1300°C and 196 MPa. The former ceramics have a fracture toughness ( K IC ) of 3.3 MPa ·m1/2 and a bending strength (σb ) of 400 MPa. In the latter materials almost all of the ZrO2 (2Y) grains (0.36–0.41 μm) are located in the grain boundaries of CrN (∼4.6 μm). The values of K IC (6.1 MPa · m1/2 ) and σb (1070 MPa) are obtained in the composites containing 50 vol% ZrO2 (2Y). 相似文献
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14.
Crack resistance characteristics and fatigue properties have been studied in four types of Y2 O3 –TZP ceramics including one containing Al2 O3 . The largely linear-elastic behavior connected with the very small transformation zone (<5 μm) explains the absence of any resistance-curve behavior and the flaw-controlled strength. The crack resistance shows high sensitivity to environment-induced subcritical crack growth. This influence is also operative in both types of fatigue experiments, i.e., under static and cyclic stresses, leading to reduced fatigue thresholds compared with K IC . While for static conditions a benefit is observed from enhanced t-m ZrO2 transformation, cyclic stresses provoke an additional fatigue effect. However, if the cyclic stresses are restricted to subthreshold values, cyclic stress-induced effects in the process zone provide an improvement of the materials being visible as a strengthening effect. 相似文献
15.
Seeding a mixture of boehmite (AIOOH) and colloidal ZrO2 with α-alumina particles and sintering at 1400°C for 100 min results in 98% density. The low sintering temperature, relative to conventional powder processing, is a result of the small alumina particle size (∼0.3 μm) obtained during the θ-to α-alumina transformation, homogeneous mixing, and the uniform structure of the sol-gel system. Complete retention of pure ZrO2 in the tetragonal phase was obtained to 14 vol% ZTA because of the low-temperature sintering. The critical grain size for tetragonal ZrO2 was determined to be ∼0.4 μm for the 14 vol% ZrO2 —Al2 O3 composite. From these results it is proposed that seeded boehmite gels offer significant advantages for process control and alumina matrix composite fabrication. 相似文献
16.
Applying an Eshelby approach, the internal micromechanical stresses within an SiC-inclusion-reinforced (platelet to whisker geometries) polycrystalline alumina matrix composite were calculated. The results are compared to the experimental residual stress measurements of a SiC-whisker-reinforced Al2 O3 by Predecki, Abuhasan, and Barrett and found to be in excellent agreement. The calculations are then extended to SiC-reinforced composites with polycrystalline mullite, silicon nitride, and cordierite matrices. It is concluded that the internal stresses are significantly influenced by the inclusion geometry as well as the thermoelastic differences between the inclusion and the matrix and also the volume fraction. 相似文献
17.
Kazuki Okada Yu-ichi Yoshizawa Taketo Sakuma 《Journal of the American Ceramic Society》1991,74(11):2820-2823
Grain-size distribution in various Al2 O3 ─ZrO2 (2.5 mol% Y2 O3 ) ceramics during high-temperature annealing was examined. In alumina-rich alloys, the grain size of major and minor phases was very different, while grain size was almost uniform in zirconia-rich alloys. This difference in grainsize distribution was related to the difference in grain growth rate of the major phase and to the effectiveness of grain-boundary pinning by minor-phase grains. 相似文献
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Our analysis of the microwave dielectric properties of the δ-Bi2 O3 –Nb2 O5 solid solution (δ-BNss ) showed a continuous increase in permittivity and dielectric losses with an increasing concentration of Nb2 O5 . The only discontinuity was found for the temperature coefficient of resonant frequency, which is negative throughout the entire homogeneity range but reaches a minimum value for the sample with 20 mol% Nb2 O5 . At the same composition there is a discontinuity in the grain size of the δ-BNss ceramics. For the sample containing 25 mol% Nb2 O5 two structural modifications were observed. A single-phase tetragonal Bi3 NbO7 , in the literature referred to as a Type-III phase, is formed in a very narrow temperature range from 850° to 880°C. A synthesis performed below or above this temperature range resulted in the formation of the end member of the δ-BNss homogeneity range. Compared with the δ-BNss the Bi3 NbO7 ceramics exhibit lower microwave dielectric losses, an increased conductivity, and a positive temperature coefficient of resonant frequency. 相似文献