共查询到20条相似文献,搜索用时 15 毫秒
1.
Jiang Li Yubai Pan Yusong Wu Huamin Kou Jingkun Guo 《International Journal of Applied Ceramic Technology》2007,4(3):276-284
High-quality alumina ceramics were fabricated by a hot pressing with MgO and SiO2 as additives using α-Al2 O3 -seeded nanocrystalline γ-Al2 O3 powders as the raw material. Densification behavior, microstructure evolution, and mechanical properties of alumina were investigated from 1250°C to 1450°C. The seeded γ-Al2 O3 sintered to 98% relative density at 1300°C. Obvious grain growth was observed at 1400°C and plate-like grains formed at 1450°C. For the 1350°C hot-pressed alumina ceramics, the grain boundary regions were generally clean. Spinel and mullite formed in the triple-grain junction regions. The bending strength and fracture toughness were 565 MPa and 4.5 MPa·m1/2 , respectively. For the 1300°C sintered alumina ceramics, the corresponding values were 492 MPa and 4.9 MPa·m1/2 . 相似文献
2.
Kyeong-Sik Cho Young-Wook Kim † Heon-Jin Choi June-Gunn Lee 《Journal of the American Ceramic Society》1996,79(6):1711-1713
A process based on liquid-phase sintering and subsequent annealing for grain growth is presented to obtain in situ -toughened SiC-30 wt% TiC composites. Its microstructures consist of uniformly distributed elongated α-SiC grains, matrixlike TiC grains, and yttrium aluminum garnet (YAG) as a grain boundary phase. The composites were fabricated from β-SiC and TiC powders with the liquid forming additives of A12 O3 and Y2 O3 by hot pressing. During the subsequent heat treatment, the β→α phase transformation of SiC led to the in situ growth of elongated α-SiC grains. The fracture toughness of the SiC-30 wt% TiC composites after 6-h annealing was 6.9 MPa-m1/2 , approximately 60% higher than that of as-hot-pressed composites (4.4 MPa-m1/2 ). Bridging and crack deflection by the elongated α-SiC grains appear to account for the increased toughness of this new class of composites. 相似文献
3.
β-SiC powder containing 6 wt% A12 O3 and 4 wt% Y2 O3 as sintering additives was pressureless sintered at 2000°C for 1 h (AYE-SiC) and 3 h (AYP-SiC). AYE-SiC consisted of an equiaxed grain structure and AYP-SiC exhibited a micro-structure with platelike grains as a result of grain growth related to β→α phase transformation during sintering, R -curve behavior and flaw tolerance for these silicon carbides were evaluated by the indentation-strength technique. For comparison, the R -curve behavior of conventional sintered, boron- and carbon-doped SiC (SS-SiC) was evaluated. AYE-SiC and AYP-SiC exhibited rising R -curve behavior with toughening exponents of m = 0.042 and m = 0.135, respectively. AYP-SiC exhibited better flaw tolerance and more sharply rising R -curve behavior than AYE-SiC. The more sharply rising R -curve behavior and the better flaw tolerance of AYP-SiC were attributed mainly to grain bridging of crack faces by platelike grains. Because of the high degree of transgranular fracture, SS-SiC exhibited a flat R -curve despite a microstructural feature with platelike grains. 相似文献
4.
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
5.
Xue-Ning Huang Chu Kun Kuo Patrick S. Nicholson 《Journal of the American Ceramic Society》1995,78(4):892-896
An epitaxial β-alumina crystal growth method was used to modify α-AI2 O3 platelet surfaces before inclusion as a reinforcing phase in partially stabilized zirconia (3Y-TZP). The as-grown surface phase was Na-β"-AI2 O3 . This was converted to Ca-β"-AI2 O3 by ion exchange, as the latter is more temperature-stable at composite sintering temperatures. The conditions of formation, thermal stability, and chemical compatibility of these interfacial phases were examined. α-AI2 O3 platelets with Ca-β"-AI2 O3 film were incorporated into 3Y-TZP. The β"-AI2 O3 /ZrO2 interface was found to promote platelet debonding and pullout, thus enhancing the α-AI2 O3 platelet/crack interactions during the fracture process. 相似文献
6.
V. A. Izhevskyi A. H. A. Bressiani J. C. Bressiani 《Journal of the American Ceramic Society》2005,88(5):1115-1121
A series of silicon carbide-based ceramics with different sintering additives were liquid-phase sintered to high densities. Yb2 O3 in combination with AlN was used as the additive, instead of the commonly used Y2 O3 –AlN, to improve the refractoriness of the secondary phase. Thermo-chemical decomposition of AlN was sufficiently suppressed with the use of nitrogen overpressure and reasonable weight loss was achieved in the different additive containing SiC ceramics without a reactive powder bed. Use of the heavier rare-earth element modified the liquid phase formed during sintering and reduced the phase transformation controlled grain growth rate, compared with Y2 O3 doped materials. It also permitted microstructure tailoring through post-sintering heat treatments in nitrogen. Materials with self-reinforced microstructures, formed as a result of anisotropic grain growth, were obtained. Improved fracture toughness (4.5–5 MPa/m1/2 ) and good flexural strength retention up to 1400°C were also observed. 相似文献
7.
Tzer-Shin Sheu 《Journal of the American Ceramic Society》1994,77(9):2345-2353
The in situ β-Si3 N4 /α'-SiAlON composite was studied along the Si3 N4 –Y2 O3 : 9 AlN composition line. This two phase composite was fully densified at 1780°C by hot pressing Densification curves and phase developments of the β-Si3 N4 /α'-SiAlON composite were found to vary with composition. Because of the cooperative formation of α'-Si AlON and β-Si3 N4 during its phase development, this composite had equiaxed α'-SiAlON (∼0.2 μm) and elongated β-Si3 N4 fine grains. The optimum mechanical properties of this two-phase composite were in the sample with 30–40%α', which had a flexural strength of 1100 MPa at 25°C 800 MPa at 1400°C in air, and a fracture toughness 6 Mpa·m1/2 . α'-SiAlON grains were equiaxed under a sintering condition at 1780°C or lower temperatures. Morphologies of the α°-SiAlON grains were affected by the sintering conditions. 相似文献
8.
Microstructural Evolution in Liquid-Phase-Sintered SiC: Part I, Effect of Starting Powder 总被引:1,自引:0,他引:1
Huiwen Xu Tania Bhatia Swarnima A. Deshpande Nitin P. Padture Angel L. Ortiz Francisco L. Cumbrera 《Journal of the American Ceramic Society》2001,84(7):1578-1584
The effect of starting SiC powder (β-SiC or α-SiC), with simultaneous additions of Al2 O3 and Y2 O3 , on the microstructural evolution of liquid-phase-sintered (LPS) SiC has been studied. When using α-SiC starting powder, the resulting microstructures contain hexagonal platelike α-SiC grains with an average aspect ratio of 1.4. This anisotropic coarsening is consistent with interface energy anisotropy in α-SiC. When using β-SiC starting powder, the β→α phase transformation induces additional anisotropy in the coarsening of platelike SiC grains. A strong correlation between the extent of β→α phase transformation, as determined using quantitative XRD analysis, and the average grain aspect ratio is observed, with the maximum average aspect ratio reaching 3.8. Based on these observations and additional SEM and TEM characterizations of the microstructures, a model for the growth of these high-aspect-ratio SiC grains is proposed. 相似文献
9.
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
10.
Electroconductive Al2 O3 –NbN ceramic composites were prepared by hot pressing. Dense sintered bodies of ball-milled Al2 O3 –NbN composite powders were obtained at 1550°C and 30 MPa for 1 h under a nitrogen atmosphere. The bending strength and fracture toughness of the composites were enhanced by incorporating niobium nitride (NbN) particles into the Al2 O3 matrix. The electrical resistivity of the composites decreased with increasing amount of NbN phase. For a 25 vol% NbN–Al2 O3 composite, the values of bending strength, fracture toughness, Vickers hardness, and electrical resistivity were 444.2 MPa, 4.59 MPa·m1/2 , 16.62 GPa, and 1.72 × 10−2 Ω·cm, respectively, making the composite suitable for electrical discharge machining. 相似文献
11.
The microstructure and humidity-sensitive characteristics of α -Fe2 O3 porous ceramic were investigated. Microporous α -Fe2 O3 powders were obtained by controlling the topotactic decomposition reaction of α -FeOOH. Water vapor adsorption thermogravimetrical experiments were carried out in the relative humidity (rh) range 0% to 95% on the α -Fe2 O3 powder and the 900°C sintered compact. The microstructure was investigated by SEM, TEM, Hg intrusion, and N2 adsorption porosimetry techniques. The humidity sensitivity was investigated by the impedance measurements technique in 0% to 95% rh on the compacts sintered at 50°C steps in the 850° to 1100°C range. Humidity response was found to be affected by the microstructure, i.e., the characteristics of the precursor powders and sintering temperatures. 相似文献
12.
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
13.
Gan Feng Tu Zhi Tong Sui Qiang Huang Chang Zhen Wang 《Journal of the American Ceramic Society》1992,75(4):1032-1034
Y-PSZ ceramics with 5 wt% Al2 O3 were synthesized by a sol–gel route. Experimental results show that powders of metastable tetragonal zirconia with 2.7 mol% Y2 O3 and 5 wt% Al2 O3 can be fabricated by decomposing the dry gel powder at 500°C. Materials sintered in an air atmosphere at 1500°C for 3 have high density (5.685 g/cm3 ), high content of metastable tetragonal zirconia (>96%), and high fracture toughness (8.67 MPa.m1/2 ). Compared with the Y-PSZ ceramics, significant toughening was achieved by adding 5 wt% Al2 O3 . 相似文献
14.
Asoke C. D. Chaklader Sankar Das Gupta Edmond C. Y. Lin Boris Gutowski 《Journal of the American Ceramic Society》1992,75(8):2283-2285
Al2 O3 and SiC composite materials have been produced from mixtures of aluminosilicates (both natural minerals and synthetic) and carbon as precursor materials. These composites are produced by heating a mixture of kaolinite (or synthetic aluminosilicates) and carbon in stoichiometric proportion above 1550°C, so that only Al2 O3 and SiC remain as the major phases. A similar process has also been used for synthesizing other composite powders having mixtures of Al2 O3 , SiC, TiC, and ZrO2 in different proportions (all compounds together or selective mixtures of some of them), as desired. The microstructure of hot-pressed dense compacts, produced from these powders, revealed that the SiC phase is distributed very homogeneously, even occasionally within Al2 O3 grains on a nanosize scale. The homogeneous distribution of SiC particles within the system produced high fracture toughness of the hot-pressed material (KIC ∼ 7.0 MPa · m1/2 ) and having Vicker's hardness values greater than 2000 kgf/mm2 . 相似文献
15.
Anteneh Kebbede John Parai Altaf H. Carim 《Journal of the American Ceramic Society》2000,83(11):2845-2851
Microstructural changes caused by doping α-Al2 O3 with small amounts of SiO2 and TiO2 added singly or together were investigated. When they were sintered at 1450°C for 120 min, singly doped samples developed equiaxed microstructures, but codoped material developed an anisotropic microstructure that contained platelike grains with an average aspect ratio of 3.4. The development of anisotropy thus resulted from a cooperative effect of silicon and titanium. Amorphous material was present at most grain boundaries in the silicon-doped sample. In the codoped sample, only boundaries that exhibited a basal facet were penetrated by amorphous material. Energy dispersive X-ray spectroscopy analysis showed strong titanium enrichment at the edges of platelets. Additional experiments demonstrated that the volume fraction of highly anisotropic platelike grains interspersed with equiaxed grains could be adjusted by using varying amounts of titanium with a constant amount of silicon content. The fracture toughnesses of such materials increased as the structure became more anisotropic. 相似文献
16.
In Situ-Toughened Silicon Carbide 总被引:10,自引:0,他引:10
Nitin P. Padture 《Journal of the American Ceramic Society》1994,77(2):519-523
A new processing strategy based on atmospheric pressure sintering is presented for obtaining dense SiC-based materials with microstructures consisting of (i) uniformly distributed elongate-shaped α-SiC grains and (ii) relatively high amounts (20 vol%) of second-phase yttrium aluminum garnet (YAG). This strategy entails the sintering of β-SiC powder doped with α-SiC, Al2 O3 , and Y2 O3 . The Al2 O3 and Y2 O3 aid in the liquid-phase sintering of SiC and form in situ YAG, which has a significant thermal expansion mismatch with SiC. During a subsequent grain-growth heat treatment, it is postulated that the α-SiC "seeds" assist in controlling in situ growth of the elongated α-SiC grains. The fracture pattern in the in situ -toughened SiC is intergranular with evidence of copious crack-wake bridging, akin to toughened Si3 N4 ceramics. The elongate nature of the α-SiC grains, together with the high thermal-residual stresses in the microstructure, enhance the observed crack-wake bridging. This bridging accounts for a measured twofold increase in the indentation toughness of this new class of in situ -toughened SiC relative to a commercial SiC. 相似文献
17.
Yoshihiko Takano Masaru Yoshinaka Ken Hirota Osamu Yamaguchi 《Journal of the American Ceramic Society》2001,84(10):2445-2447
Intermetallic CoAl powder has been prepared via self-propagating high-temperature synthesis (SHS). Dense CoAl materials (99.6% of theoretical) with the combined additions of ZrO2 (3Y) and Al2 O3 have been fabricated via spark plasma sintering (SPS) for 10 min at 1300°C and 30 MPa. The microstructures are such that tetragonal ZrO2 (0.3 μm) and Al2 O3 (0.5 μm) particles are located at the grain boundaries of the CoAl (8.5 μm) matrix. Improved mechanical properties are obtained; especially the fracture toughness and the bending strength of the materials with ZrO2 (3Y)/Al2 O3 = 16/4 mol% are 3.87 MPa·m1/2 and 1080 MPa, respectively, and high strength (>600 MPa) can be retained up to 1000°C. 相似文献
18.
WILLIAM C. HAGEL P. J. JORGENSEN D. S. TOMALIN 《Journal of the American Ceramic Society》1966,49(1):23-26
Since the difference between oxygen-ion and cation diffusion coefficients is greater for α-Cr2 O3 than for α-Fe2 O3 or α-Al2 O3 , a study of initial-sintering kinetics was undertaken to show unequivocally which species is rate controlling. Fine powders of α-Cr2 O3 , obtained by thermal decomposition of reagent-grade (NH4 )2 Cr2 O7 , were lightly compacted and their isothermal rates of shrinkage were determined between 1050° and 1300°C. Resultant data follow volume-diffusion sintering models, and calculated diffusion coefficients agree with, those measured for oxygen ions in α-Cr2 O3 . There is little evidence that oxygen diffusion along grain boundaries becomes so enhanced that chromium ions are left in control of the process. 相似文献
19.
Rabindra N. Das Amit Bandyopadhyay Susmita Bose 《Journal of the American Ceramic Society》2001,84(10):2421-2423
Nanocrystalline α-Al2 O3 ceramic powders have been prepared from an aqueous solution of aluminum nitrate and sucrose. Soluble Al ion-sucrose solution forms the precursor material once it is completely dehydrated. Heat treatment of the dehydrated precursors at low temperature (600°C) results in the formation of porous single-phase α-Al2 O3 . The precursor and heat-treated powders have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and BET surface area analysis. The phase-pure nanocrystalline α-Al2 O3 particles had an average specific surface area of >190 m2 /g, with an average pore size between 18 and 25 nm. 相似文献
20.
Xudong Sun Ji-Guang Li Shiwen Guo Zhimeng Xiu Kai Duan Xiao Zhi Hu 《Journal of the American Ceramic Society》2005,88(6):1536-1543
Al2 O3 /SiC ceramic nanocomposites were fabricated from nanocrystalline Al2 O3 (10 nm in diameter) and SiC (15 nm in diameter) powders, and a theoretical model of intragranular particle residual stress strengthening was investigated. The SiC nanoparticles in the Al2 O3 grains create a normal compressive stress at the grain boundaries and a tangential tensile stress in the Al2 O3 grains, resulting in the "strengthening" of the grain boundaries and "weakening" of the grains. The model gives a good explanation of the experimental results of the authors and others which are difficult to be explained by the existing strengthening models, i.e. the maximum strength is normally achieved at about 5 vol% of SiC particles in the Al2 O3 –SiC ceramic nanocomposites. According to the model, there exists an optimum amount of SiC for strengthening, below which the grain boundaries are not fully "strengthened" and the fracture is mainly intergranular, above which the grains are "weakened" too much and the fracture is mainly transgranular, and at which the fracture is a mixture of intergranular and transgranular. 相似文献