共查询到20条相似文献,搜索用时 15 毫秒
1.
H. SCHUBERT 《Journal of the American Ceramic Society》1986,69(3):270-271
The transformability of the grains in tetragonal zirconia polycrystals is determined by thermal stresses (eigenstresses) which develop because of anisotropic expansion behavior of the tetragonal grains on cooling. Anisotropic thermal expansion coefficients based on lattice parameter determinations at room temperature and 600° and 800°C are presented for tetragonal zirconia containing 2 and 3 mol% Y2 O3 . The sources of errors in these data are discussed. 相似文献
2.
Motohiro Suganuma 《Journal of the American Ceramic Society》1995,78(11):2889-2896
Scanning acoustic microscopy (SAM) has been applied to investigate Vickers indentation-induced damage in Y2 O3 -stabilized tetragonal zirconia polycrystal (Y-TZP). The leaky Rayleigh wave velocity, vR , around the indentation is determined from the V( Z ) curve technique. A considerable anisotropy in vR is observed within the elastic/plastic zone which results from the indentation-induced residual stresses. In contreast, an isotropic reduction in vR is found within the indentation core, implying the presence of microcracks. Furthermore, the SAM observations reveal that the elasic/plastic boundary is axisymmetric with respect to the loading axis and that its radius is 1.2 times as large as the indentation half-diagonal. These results are discussed in terms of an analysis based on the pressurized-sphericalcavity model. 相似文献
3.
Michiyuki Yoshida Yutaka Shinoda Takashi Akatsu Fumihiro Wakai 《Journal of the American Ceramic Society》2002,85(11):2834-2836
Ultrafine-grained monoclinic ZrO2 polycrystals (MZP) and 3-mol%-Y2 O3 -stabilized tetragonal ZrO2 polycrystals (3Y-TZP) were obtained by hot isostatic pressing (HIP). Both MZP and TZP were "high-purity" materials with impurities less than 0.1 wt%. The deformation behavior was studied at 1373 K, which was lower than the monoclinic ↔ tetragonal transition temperature. The stress exponent of 3Y-TZP with grain size of 63 nm was 3 in the higher stress region, and increased from 3 to 4 with decreasing stress. The deformation of MZP was characterized by a stress exponent of 2.5 over a wide stress range. The strain rate of 3Y-TZP was slower than that of MZP by 1 order of magnitude. It was suggested that either the doped yttrium or the difference in the crystal structure affected the diffusion coefficients of ZrO2 . 相似文献
4.
Yttria-containing tetragonal zirconia polycrystals with low thermal stability showed plastic deformation with a maximum bending strain of 0.8% due to the stress-induced tetragonal to monoclinic transformation. The strain rate depended on applied stress and temperature. The temperature at which the transformation rate is maximum increases with increasing applied stress. Changes in microstructure and crystallographic structure after plastic deformation were examined by transmission electron microscopy and X-ray analyses. The mechanism of plastic deformation is discussed in relation to the tetragonal to monoclinic transformation. 相似文献
5.
TAKAKI MASAKI 《Journal of the American Ceramic Society》1986,69(7):519-522
Yttria-partially-stabilized zirconia (Y-PSZ) materials containing 2.5, 3.0, and 5.0 mol% of Y2 O3 prepared by hot pressing were subjected to ageing in air for >10 h at temperatures in the range of 800°C and 1200°C. The sintered materials were measured to determine the mechanical properties and microstructures and analyzed for trace elements. A sharp reduction in bending strength was observed after the ageing, the cause for which was suggested to be the formation of cavities produced by the oxidation of carbon. 相似文献
6.
Krzysztof Haberko Waldemar Pyda Jan Piekarczyk Miroslaw M. Bucko 《Journal of the American Ceramic Society》1992,75(5):1272-1275
Fully tetragonal and sintered 13 mol% TiO2 ─3 mol% Y2 O3 ─84 mol% ZrO2 was thermally treated at 1300°C for 1 h in argon in the presence of carbon. No phase changes occurred on the as-received surface and in the bulk of the material, but t → m transformation occurred on polished surfaces under reducing conditions, and it resulted in increased fracture toughness, Young's modulus, and modulus of rigidity. Deoxidation of the system occurred and 0.174 wt% of carbon was found in the sample. This seemed to stabilize the tetragonal phase. 相似文献
7.
Robert G. Hill Christopher Goat David Wood 《Journal of the American Ceramic Society》1992,75(4):778-785
A SiO2 ─Al2 O3 ─CaO─CaF2 ionomer glass was investigated using thermal analysis, X-ray diffraction, and scanning electron microscopy. The purpose of this investigation was to control the susceptibility of the glass to acid attack. The differential thermal analysis trace exhibited a sharp glass transition at about 645°C and two exotherms. The first exotherm corresponded to liquid–liquid phase separation followed by crystallization of fluorite. The second, much larger, exotherm was the result of crystallization of the remaining glass phase to form anorthite. Prolonged heat treatment below the glass-transition temperature demonstrated that crystallization of fluorite can occur without prior liquid–liquid phase separation. 相似文献
8.
The phase diagram for the CuO-rich part of the La2 O3 ─CuO join was redetermined. La2 Cu2 O5 was found to have a lower limit of stability at 1002°± 5°C and an incongruent melting temperature of ∼1035°C. LagCu7 O19 had both a lower (1012°± 5°C) and an upper (1027°± 5°C) limit of stability. Subsolidus phase relations were studied in the La2 O3 ─CuO─CaO system at 1000°, 1020°, and 1050°C in air. Two ternary phases, La1.9 Ca1.1 Cu2 O5.9 and LaCa2 Cu3 O8.6 , were stable at these temperatures, with three binary phases, Ca2 CuO3 , CaCu2 O3 , and La2 CuO4 . La2 Cu2 O5 and La8 Cu7 O19 were stable only at 1020°C, and did not support solid-solution formation. 相似文献
9.
Subsolidus Phase Relationships in Part of the System Si,Al,Y/N,O: The System Si3 N4 ─AIN─YN─Al2 O3 ─Y2 O3
Wei-Ying Sun Tseng-Ying Tien Tung-Sheng Yen 《Journal of the American Ceramic Society》1991,74(11):2753-2758
The subsolidus phase relationships in the system Si,Al,Y/N,O were determined. Thirty-nine compatibility tetrahedra were established in the region Si3 N4 ─AIN─Al2 O3 ─Y2 O3 . The subsolidus phase relationships in the region Si3 N4 ─AIN─YN─Y2 O3 have also been studied. Only one compound, 2YN:Si3 N4 , was confirmed in the binary system Si3 N4 ─YN. The solubility limits of the α'─SiAION on the Si3 N4 ─YN:3AIN join were determined to range from m = 1.3 to m = 2.4 in the formula Y m /3 Si12- m Al m N16 . No quinary compound was found. Seven compatibility tetrahedra were established in the region Si3 N4 ─AIN─YN─Y2 O3 . 相似文献
10.
The compositional range for glass formation below 1600°C in the Sm2 O3 ─Al2 O3 ─SiO2 system is (9–25)Sm2 O3 ─(10–35)Al2 O3 ─(40–75)SiO2 (mol%). Selected properties of the Sm2 O3 ─Al2 O3 ─SiO2 (SmAS) glasses were evaluated as a function of composition. The density, refractive index, microhardness, and thermal expansion coefficient increased as the Sm2 O3 content increased from 9 to 25 mol%, the values exceeding those for fused silica. The dissolution rate in 1 N HCl and in deionized water increased with increasing Sm2 O3 content and with increasing temperature to 70°C. The transformation temperature ( T g ) and dilatometric softening temperature ( T d ) of the SmAS glasses exceeded 800° and 850°C, respectively. 相似文献
11.
Cristina Leonelli Tiziano Manfredini Mariano Paganelli Gian Carlo Pellacani Jose Luis Amoros Albaro Jose Emilio Enrique Navarro Maria Jose Orts Silvia Bruni Franco Cariati 《Journal of the American Ceramic Society》1991,74(5):983-987
In order to verify the possibility of using glass-ceramic materials as tile coatings, the devitrification processes of three industrial formulations belonging to the Li2 O─Al2 O3 ─SiO2 glass-ceramic system were investigated by differential thermal analysis, X-ray diffractometry, scanning electron microscopy, and IR spectroscopy. Compositional variations were made by addition of large amounts of MgO or CaO or PbO (ZnO) oxides as well as through smaller additions of other oxides. In these systems the surface crystallization contributes appreciably to the bulk crystallization mechanism. All the systems investigated show a high tendency toward crystallization even at very high heating rates, developing a very close network of interlocked crystals of synthetic β-spodumene-silica solid solutions (LiAlSi4 O10 ). The results of this research are expected to establish the conditions under which these glass-ceramic systems can be practically used as tile glazes. 相似文献
12.
Takashi Wakasugi Fumitaka Tsukihashi Nobuo Sano 《Journal of the American Ceramic Society》1991,74(7):1650-1653
The BN solubilities for B2 O3 , B2 O3 ─SiO2 , and B2 O3 ─CaO systems have been measured mainly at 1823 K using a graphite crucible. The capability of the systems for nitrogen dissolution is compared with that of silicate systems in terms of nitride capacity. The dependence of nitrogen solubility in molten CaO containing 15 mol% of B2 O3 on oxygen and nitrogen partial pressures is also investigated. It has been found that there are two mechanisms for nitrogen dissolution, namely as chemically bonded nitrogen and as physically dissolved nitrogen gas. 相似文献
13.
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
14.
15.
Yukishige Kitano Yuuji Mori Akira Ishitani Takaki Masaki 《Journal of the American Ceramic Society》1988,71(8):382-C
Structural changes of 2.5-mol%-Y2 O3 -stabilized tetragonal ZrO2 polycrystal fractured surfaces, as well as ground, polished, and annealed surfaces, were studied by X-ray diffraction. Much greater intensity of the (200) tetragonal peak than (002) was found on the thin surface layer of the ground specimen, but not on the fracture surface. The intensity changes were discussed in relation to the toughening mechanism. 相似文献
16.
The compression creep behavior of Y2 O3 -stabilized ZrO2 (YSZ) was studied at temperatures to 2000 ° C. The function of Y2 O3 content and grain size was tested in specimens with various impurity concentrations and porosity distributions. For relatively fine-grained specimens, creep rates increased with the 1.5 power of the applied stress at low stresses and with the third power at high stresses. The results for coarse-grained specimens can, in general, be fit by the cube dependence. The 1.5 power can be reduced to a linear dependence by correcting for an apparent threshold stress, which decreases with increasing temperature. Creep activation energies for YSZ are 128 ± 10 kcal/mol, independent of Y2 O3 content, impurity level, grain size, and porosity distribution. In addition, over a broad range of temperatures and stresses the absolute values of the steady-state creep rates are influenced only by grain size and O2 partial pressure. 相似文献
17.
Transformation plasticity in CeO2 -stabilized tetragonal zirconia polycrystals due to the tetragonal-to-monoclinic transformation was studied by inducing volumetric and shear deformation under compression and bending between the burst temperature of martensite (monoclinic) formation ( Mb ) and the burst temperature of austenite (tetragonal) formation ( Ab ). The stress-strain curve features a load drop, a perfect plastic regime, and an extended strain-hardening regime before the exhaustion of transformation. Macroscopic shear bands formed in the perfect plastic regime. The yield stress has a strong, positive pressure and temperature sensitivity but is strain-rate sensitive only in the last stage of deformation. These results are rationalized in terms of stress assistance to the transformation which, in a homogeneous tetragonal polycrystal, may propagate autocatalytically. Autocatalysis can be impeded by a second phase, such as monoclinic ZrO2 or Al2 O3 , and is suppressed at higher temperature. Flow localization is found to precede and precipitate crack formation. As a result, the actual fracture energy is much less than the total plastic work. The implications of stress-assisted, autocatalytic transformation on strength and toughness are explored. 相似文献
18.
Dae-Joon Kim Paul F. Becher Camden R. Hubbard 《Journal of the American Ceramic Society》1993,76(11):2904-2908
Tetragonal ZrO2 ( t -ZrO2 ) solid solutions were prepared with addit ons of 2 mol% Y2 O3 plus up to 0.45 mol% Nb2 O5 . The thermal expansion coefficients in both the a- and c -axis lattice directions increased with Nb2 O5 alloying and the thermal expansion in the c -axis direction was greater than that in the a -axis direction over the entire composition range. This anisotropic thermal expansion behavior was related to the 4-fold coordination of Nb5+ with oxygen ions in t -ZrO2 solid solutions in the system ZrO2 –Y2 O3 –Nb2 O5 . The fracture toughness continuously increased with Nb2 O5 alloying and suggested that the c/a axial ratio is a more significant factor than the internal stress that arises from the thermal expansion anisotropy, in the determination of the transformability of t -ZrO2 in this system. 相似文献
19.
Koji Morita Keijiro Hiraga Yoshio Sakka 《Journal of the American Ceramic Society》2002,85(7):1900-1902
High-strain-rate superplasticity is attained in a 3-mol%-Y2 O3 -stabilized tetragonal ZrO2 polycrystal (3Y-TZP) dispersed with 30 vol% MgAl2 O4 spinel: tensile elongation at 1823 K reached >300% at strain rates of 1.7 × 10−2 – 3.3 × 10−1 s−1 . The flow behavior and the microstructure of this material indicate that the MgAl2 O4 dispersion should enhance accommodation processes necessary for grain boundary sliding. Such an effect is assumed to arise from an enhancement of the cation diffusion by the dissolution of Al and Mg ions into the ZrO2 matrix and from stress relaxation due to the dispersed MgAl2 O4 grains. 相似文献
20.
The phase composition of fine ZrO2 and ZrO─Y2 O3 powders prepared by the process of spray pyrolysis was detected using XRD. An interesting phenomenon has been observed. In this paper, the influence of the temperature and carrier gas flux on the phase composition of as-prepared powders is described. The formation and transformation mechanisms of the powder phase in the process are also discussed. 相似文献