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Koji Tsukuma Kuniyoshi Ueda Kenichi Matsushita Masahiko Shimada 《Journal of the American Ceramic Society》1985,68(2):56-C-
The temperature dependence of bending strength, fracture toughness, and Young's modulus of composite materials fabricated in the ZrO2 (Y2 O3 )-Al2 O3 system were examined. The addition of A1203 enhanced the high-temperature strength. Isostatically hot-pressed, 60 wt% ZrO2 (2 mol% Y2 O3 )/40 wt% Al2 O3 exhibited an extremely high strength, 1000 MPa, at 1000°C. 相似文献
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A tracer sectioning technique was used to measure cation self-diffusion coefficients in fully dense polycrystalline Ya O3 and Er2 Os under oxidizing conditions. The results are described by the relations for Y2 O3 (1400° to 1670°C), and for Er2 O3 (1400° to 1700°C). The greater activation energy for erbium diffusion in erbia may be partly attributable to a mass effect. 相似文献
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The eutectic composition between Y4 Al2 O9 and Y2 O3 was determined using electron probe microanalysis (EPMA) on directionally solidified specimens with hypo- and hypereutectic compositions. The microstructures of the specimens as a function of composition differ considerably with small deviation from the eutectic composition (70.5 mol% Y2 O3 and 29.5 mol% Al2 O3 ). Based on the current results and other published data, the pseudobinary system between Al2 O3 and Y2 O3 is revised. 相似文献
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Koji Tsukuma Kuniyoshi Ueda Masahiko Shimada 《Journal of the American Ceramic Society》1985,68(1):4-C-5
Composites of Al2 O3 and Y2 O3 partially-stabilized ZrO2 were isostatically hot-pressed using submicrometer powders as the starting material. The addition of Al2 O3 resulted in a large increase in bending strength. The average bending strength for a composite containing 20 wt% Al2 O3 was 2400 MPa, and its fracture toughness was 17 MN·w−3/2 相似文献
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Ken Ando Yasumichi Oishi Hiroyuki Hase Koichi Kitazawa 《Journal of the American Ceramic Society》1983,66(12):222-C
Self-diffusion coefficients of the oxygen ion in single-crystal Y2 O3 were determined by the gas-solid isotope exchange technique. The results in the range 1100° to 1500°C are described by D=7.3 X 10-6 exp [-19l(kJ/mol)/RT] cm2 /s. Comparison of the results with those for oxides with the fluorite-type structure indicates that the regularly arranged vacant anion sites in the C-type structure do not contribute eflectively to oxygen ion diffusion . 相似文献
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Jenn-Ming Yang S. M. Jeng Sekyung Chang 《Journal of the American Ceramic Society》1996,79(5):1218-1222
The strength and fracture of a directionally solidified Y3 Al5 O12 /Al2 O3 eutectic fiber were investigated. The fiber was grown continuously by an edge-defined film-fed growth technique. The microstructure was characterized using X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The tensile strength and Weibull's modulus of the eutectic fibers were determined in the as-fabricated state and after extended thermal exposure at 1460°C in air. Fractographic analysis was used to identify and classify the strength-limiting mechanisms. The fracture toughness and crack growth behavior were characterized by an indentation technique. A fracture mechanics analysis was also used to establish the relationships between surface flaw size, tensile strength, and fracture toughness of the fiber. 相似文献
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The phase equilibrium relations in the systems Y2 O3 -Al2 O3 and Gd2 O3 -Fe2 O3 were examined. Each system has two stable binary compounds. A 3:s molar ratio garnet-type compound exists in both systems. The 1:1 distorted perovskite structure is stable in the system Gd2 O3 -Fe2 O3 but only metastable in the system Y2 O3 -AI2 O3 . This interesting example of metastable formation and persistence of a compound with ions of high Z/r values explains the discrepancies in the literature on the structure of the composition YA1O3 . A new 2:1 molar ratio cubic phase has been found in the system Y2 O3 -A12 O3 . Since silicon can be completely substituted for aluminum in this compound, the aluminum ions are presumably in fourfold coordination. 相似文献
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Kuan Zong Fung Anil V. Virkar David L. Drobeck 《Journal of the American Ceramic Society》1994,77(6):1638-1648
Cubic solid solutions in the Y2 O3 -Bi2 O3 system with ∼25% Y2 O3 undergo a transformation to a rhombohedral phase when annealed at temperatures ≤ 700°C. This transformation is composition-invariant and is thermally activated, and the product phase can propagate across matrix grain boundaries, indicating that there is no special crystallo-graphic orientation relationship between the product and the parent phases. Based on these observations, it is proposed that cubic → rhombohedral phase transformation in the Y2 O3 -Bi2 O3 system is a massive transformation. Samples of composition 25% Y2 O3 -75% Bi2 O3 with and without aliovalent dopants were annealed at temperatures ≤ 700°C for up to 10000 h. ZrO2 as a dopant suppressed while CaO and SrO as dopants enhanced the kinetics of phase transformation. The rate of cubic/rhombohedra1 interface migration (growth rate or interface velocity) was also similarly affected by the additions of dopants; ZrO2 suppressed while CaO enhanced the growth rate. Diffusion studies further showed that ZrO2 suppressed while CaO enhanced cation interdiffusion coefficient. These observations are rationalized on the premise that cation interstitials are more mobile compared to cation vacancies in cubic bismuth oxide. The maximum growth rate measured was ∼10−10 m/s, which is orders of magnitude smaller than typical growth rates measured in metallic alloys. This difference is explained in terms of substantially lower diffusion coefficients in these oxide systems compared to metallic alloys. 相似文献
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Ivar E. Reimanis M. E. Hawley T. E. Mitchell D. S. Zhou 《Journal of the American Ceramic Society》1995,78(8):2282-2286
The fracture surfaces of single-crystal Y3 A15 O12 (YAG) have been examined in detail using differential interference microscopy and atomic force microscopy. In YAG crystals grown in 1977 by the Czochralski method strikingly regular undulations of microscopic and submicroscopic dimensions (4–20 nm in amplitude, 1–20 μm in wavelength) are observed on every fracture surface. The undulations do not exhibit typical characteristics of Wallner lines; furthermore, they are not observed in identical fracture tests for YAG crystals grown in 1990 by the Czochralski method. Transmission electron microscopy reveals that the crystals grown in 1977 exhibit a periodic fluctuation of the ratio of the concentrations of aluminum to yttrium, suggesting that the fracture surface features are caused by periodic astoichiometry. 相似文献
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The fracture toughness of 3 mol% Y2 O3 -ZrO2 (3Y-PSZ) composites containing 10–30 vol% Al2 O3 with different particle sizes was investigated. It was found that Al2 O3 dispersion of up to 30 vol% increased the fracture toughness by 17% to 30%, and the toughness increase was more remarkable in the composite dispersed with Al2 O3 particles of larger sizes. By combining the effects of the dispersion toughening and phase transformation toughening, the toughness change in the present materials was theoretically predicted, which was in good agreement with the experimental data. 相似文献
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The ternary phase diagram of Al2 O3 -La2 O3 -TiO2 at 1400°C was determined with 12 compatibility triangles. Al2 O3 stabilizes the A-site-deficient La2/3 TiO3 perovskite structure. According to XRD and microstructural investigations, the solid solution extends along the La2/3 TiO3 -LaAlO3 tie line from at least 4 mol% LaAlO3 to pure LaAlO3 . With increasing LaAlO3 content, the stabilized La2/3 TiO3 structure changes from orthorombic via tetragonal to cubic. 相似文献
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Oriented samples of Al2 O3 -ZrO2 (Y2 O3 ) eutectics consisting of an alumina matrix with zirconia dispersoids were grown by directional solidification. Preferred growth directions and epitaxial relations were determined from X-ray and electron diffraction analyses. Imaging of interfaces was performed by high-resolution transmission electron microscopy on oriented platelets. Semicoherent interfaces were observed with faceting along crystallographic planes of both phases. 相似文献
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The addition of ThO2 to Y2 O3 inhibits grain growth during sintering and allows the sintering process to proceed to theoretical density by maintaining a high diffusion flux of vacancies from the pores to the grain boundaries. The inhibition of grain growth is accomplished by the segregation of ThO2 solute at the grain boundaries, causing a decrease in the grain-boundary mobility. The segregation of ThO2 at the grain boundaries can be inferred from the results of the microhardness and grain-growth studies presented. Further evidence for segregation is provided by quenching experiments and surface activity experiments. 相似文献
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Yukishige Kitano Yuuji Mori Akira Ishitani Takaki Masaki 《Journal of the American Ceramic Society》1988,71(1):34-C-
Tetragonal-to-rhombohedral stress-induced phase transformation was studied by X-ray diffraction on the ground surfaces of tetragonal zirconia polycrystals and partially stabilized zirconia containing 2.0 to 5.0 mol% Y2 O3 prepared by hot isostatic pressing. The rhombohedral phase increased with Y2 O3 content and also with hot isostatic pressing temperature. The stability of the rhombohedral phase was studied with regard to surface finish and thermal annealing. The subsequent heat treatment of the specimens was found to cause the reverse rhombohedral-to-tetragonal transformation. 相似文献