共查询到20条相似文献,搜索用时 15 毫秒
1.
Yoshikazu Suzuki Héctor A. Calderón Naoki Kondo Tatsuki Ohji 《Journal of the American Ceramic Society》2000,83(6):1346-1350
The in situ formation of magnetoplumbite-type (M-type) hexaferrites within a 3Y-TZP matrix was examined for the La2 O3 –ZnO–Fe2 O3 and BaO–Fe2 O3 systems. The formation of barium hexaferrite (Ba-M) was rapid enough at a temperature of 1300°C for 2 h to result in a uniform dispersion of fine Ba-M particles in a tetragonal zirconia polycrystal (TZP) matrix. However, the formation of lanthanum-substituted hexaferrite (La-M) was rather sluggish, despite the existence of a charge-compensating divalent oxide. The 3Y-TZP/20-wt%-BaFe12 O19 in situ composite possessed good magnetic properties, as well as moderately good mechanical properties. 相似文献
2.
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
3.
Valter Sergo 《Journal of the American Ceramic Society》2004,87(2):247-253
The stresses of laminate structures obtained by joining single layers of pure alumina (A), pure yttria-stabilized tetragonal zirconia, 3Y-TZP (Z), and an intimate mixture of alumina and zirconia (AZ) have been determined by fluorescence (in alumina) and Raman (in zirconia) piezospectroscopy. Three symmetrical stacking sequences were examined, namely, A/Z/A, A/AZ/A, and AZ/Z/AZ, with the aim of designing structures where the higher coefficient of thermal expansion (CTE) of zirconia could be used to induce compressive stress in the external layers (and ensuing tensile stress in the central layer). Two experimental sessions, 6 years apart, were conducted on the same samples, also taking care to record the spectra from the same locations; during the time elapsed between the two sessions, the samples were kept at room temperature and humidity. The stress values in alumina obtained during the more recent session were markedly different from those observed in the first session. Monoclinic zirconia ( m -zirconia) was absent in all samples in the first session, whereas up to 25 vol% zirconia could be observed during the second session. m -Zirconia could only be observed in AZ layers and not in Z layers, irrespective of the position in the stacking sequence. It was concluded that 3Y-TZP underwent spontaneous tetragonal-to-monoclinic ( t – m ) transformation, that is, "aging," when mixed with alumina at the grain-size level. Aging occurred only where pristine t -zirconia was subject to tensile stresses larger than ∼400 MPa. 相似文献
4.
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
5.
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
6.
Grain growth kinetics and grain-boundary segregation of 12Ce-TZP and 2Y-TZP, containing divalent to pentavalent cationic dopants, were studied. In all cases, normal grain growth follwing the parabolic growth relation was observed at higher temperatures. The mobility of grain boundaries was suppressed by the addition of divalent and trivalent cations, unchanged or enhanced by the addition of tetravalent and pentavalent cations. Larger cations have a stronger effect in suppressing grain growth. From ESCA, AES, and STEM analysis of the near grain-boundary regions, it is further concluded that only divalent and trivalent cations segregate. These observations can be satisfactorily rationalized using the space charge concept and the model of impurity drag. 相似文献
7.
Herbert K. Schmid 《Journal of the American Ceramic Society》1991,74(2):387-394
The microstructure and microchemistry of grain-boundary regions in (CeO2 + La2 O3 )-stabilized tetragonal ZrO2 polycrystals (Ce(La)-TZP) were studied by means of transmission electron microscopy (TEM). Evidence was found for the existence of crystalline and vitreous intergranular phases situated in small pockets at multiple grain junctions and in thin films along grain boundaries. In this ceramic system grain-boundary migration was observed in situ in the TEM in sample areas subjected to electron irradiation. Interfaces migrated away from their centers of curvature. Evidence was found for Ce de-alloying in the volume swept by the advancing boundaries. It is suggested that the coherency lattice strain brought about by a partial reduction of Ce, resulting in the diffusion of Ce3+ along grain boundaries to free surfaces, is the driving force for this phenomenon. 相似文献
8.
Superplastic deformation of tetragonal zirconia polycrystal (TZP) was investigated by compression test in the temperature range of 1000° to 1500°C. Special attention was paid to the role of the grain-boundary glass phase on hightemperature deformation behavior. A small addition of glass phase markedly improved the high-temperature deformability of TZP. Lithium silicate glass was much superior to aluminosilicate or lithium aluminum silicate glasses for lowering the high-temperature flow stress. The deformation mechanism was discussed on the basis of mechanical testing data and microstructural examinations. 相似文献
9.
Chiari Schmid Orfeo Sbaizero Valter Sergo Sergio Meriani 《Journal of the American Ceramic Society》1992,75(7):2003-2005
During an investigation of the role of alumina particles in ceria-stabilized tetragonal zirconia polycrystals (Ce-TZP)1 we observed that a group of samples (based on a Ce-TZP matrix (8.5 mol% Ceria) containing 15 vol% dispersed alumina particles), exhibited an extended plastic deformation after the first elastic response. This deformation could be retained upon a prompt unloading from a fourpoint bend jig. These deformed (bent) specimens recovered their original straight shape when heated above 200°C, exhibiting features like the shape memory effect (SME). A careful examination of the samples revealed the presence of wedgelike transformation zones intruding the bulk of the specimen inwards from the tensioned side.
In an attempt to increase the degree of bending, other samples of the same composition and microstructure have been placed under a static load and maintained under that condition for ≅15 min. The penetration depth of the transformation zone reached the opposite face of the samples and the monoclinic-phase concentration rose about 50% on both sides. Through this inwards movement, these samples, that were initially bent, showed an elongation of about 0.5% and became straightened. These samples returned to their original size after heating at ≅250°C. To get a deeper insight, samples have been examined by X-ray diffraction (XRD), differential thermal analysis (DTA), and thermodilatometry (TD). 相似文献
In an attempt to increase the degree of bending, other samples of the same composition and microstructure have been placed under a static load and maintained under that condition for ≅15 min. The penetration depth of the transformation zone reached the opposite face of the samples and the monoclinic-phase concentration rose about 50% on both sides. Through this inwards movement, these samples, that were initially bent, showed an elongation of about 0.5% and became straightened. These samples returned to their original size after heating at ≅250°C. To get a deeper insight, samples have been examined by X-ray diffraction (XRD), differential thermal analysis (DTA), and thermodilatometry (TD). 相似文献
10.
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
11.
Effect of Cation Doping on the Superplastic Flow in Yttria-Stabilized Tetragonal Zirconia Polycrystals 总被引:1,自引:0,他引:1
Junpei Mimurada Manabu Nakano Kazutaka Sasaki Yuichi Ikuhara Taketo Sakuma 《Journal of the American Ceramic Society》2001,84(8):1817-1821
The superplastic characteristics of various cation-doped yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) were examined. For 1 mol% cation doping the true stress of Y-TZP is very dependent on the ionic radii of the doped cations; for instance, smaller cation radii give rise to lower true stress when compared with the other compositions for the same grain size, strain rate, and testing temperature. The altered true stress level must be due to the change in diffusivity of the accommodation process for grain boundary sliding caused by the addition of cations in ZrO2 . The strain to failure of the doped zirconia is affected by both ionic radius and valence of the dopant cations. 相似文献
12.
Hiroki Kondo Tohru Sekino Takafumi Kusunose Tadachika Nakayama Yo Yamamoto Masashi Wada Tomohiko Adachi Koichi Niihara 《Journal of the American Ceramic Society》2003,86(3):523-525
Stability and mechanical properties of the tetragonal phase were investigated for NiO-doped yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) systems. Only 0.3 mol% of NiO in solid solution could be added to the Y-TZP while maintaining the tetragonal phase. Fracture toughness improved remarkably on addition of a small amount of NiO. Raman spectroscopy analysis around cracks introduced by Vickers indentation revealed that the amount of monoclinic phase transformed from tetragonal phase was increased. It was confirmed that fracture toughness improvement was due not only to increased grain size, but also to Y-TZP destabilization by solid solution of NiO. 相似文献
13.
Junya Kondoh Yoichi Tomii Katsuhiro Kawachi 《Journal of the American Ceramic Society》2003,86(12):2093-2102
Methods of suppressing decreased conductivity in 8 mol% Y2 O3 -stabilized–92 mol% ZrO2 (8YSZ) with aging were investigated. Different amounts of Sc2 O3 were doped into 8YSZ. The electrochemical properties of Sc2 O3 -doped 8YSZ were measured, and the microstructural and local structural changes were characterized. The present results indicate that an appropriate amount of Sc2 O3 doping, 3 or 4 mol%, effectively suppresses decreased conductivity with aging in 8YSZ. 相似文献
14.
Harushige Tsubakino Ryoichi Nozato Mitsuharu Hamamoto 《Journal of the American Ceramic Society》1991,74(2):440-443
The tetragonal-to-monoclinic martensitic phase transformation in ZrO–3 mol% Y2 O3 (PSZ) containing 0 to 12 wt% Al2 O3 was investigated by dilatometry, XRD, and SEM-EDS methods. The propagation of the transformation into the specimen interiors was suppressed by the addition of Al2 O3 . The grain size was independent of the addition of Al2 O3 . Both Y2 O3 and Al2 O3 segregated at grain boundaries. From this segregation behavior, it was suggested that a certain compound or phase of Y2 O3 –Al2 O3 could be formed at grain boundaries, which would presumably prevent the propagation of the transformation into interiors of PSZ-containing Al2 O3 . 相似文献
15.
Francisco del Monte Willa Larsen John D. Mackenzie 《Journal of the American Ceramic Society》2000,83(3):628-634
Gel-glasses of various compositions in the x ZrO2 . (10 – x )SiO2 system were fabricated by the sol–gel process. Precipitation due to the different reactivities between tetraethyl orthosilicate (TEOS) and zirconium(IV) n -propoxide has been eliminated through the use of 2-methoxyethanol as a chelating agent. Thermal treatment of these gels produced crystalline ZrO2 particles. While monoclinic is the stable crystalline phase of zirconia at low temperatures, the metastable tetragonal phase is usually the first crystalline phase formed on heat treatment. However, stability of the tetragonal phase is low, and it transforms to the monoclinic phase on further heat treatment. In this study, it has been found that the transformation temperature increases as the SiO2 content in the ZrO2 –SiO2 binary oxide increases. The most significant results were from samples containing only 2 mol% SiO2 , where the metastable tetragonal phase formed at low temperatures and remained stable over a broad temperature range. X-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy were used to elucidate the structure of these binary oxides as a function of temperature. 相似文献
16.
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
17.
Sukhvinder P. S. Badwal Fabio T. Ciacchi Michael V. Swain Viktor Zelizko 《Journal of the American Ceramic Society》1990,73(8):2505-2507
The grain-boundary resistivity of tetragonal zirconia polycrystals, which had undergone creep with different applied compressive loads and at different temperatures, has been measured with impedance spectroscopy. A stress exponent of unity was determined from strain rate versus stress data. The grain-boundary resistivity decreased significantly with increasing stress at a constant creep temperature indicating squeezing out of the glassy phase from interfaces between grains. This, however, had no effect on the activation energy for the grain-boundary resistivity. 相似文献
18.
Crack resistance characteristics and fatigue properties have been investigated in Ce-TZP ceramics with different grain sizes. The relatively low critical transformation stress allows the development of larger transformation zones (≦200 μm), leading to flaw-tolerant behavior. However, autocatalytic transformation processes are found to be bound to grain sizes beyond a critical value; transformation is then very limited in finer microstructures. Fatigue as a specific cyclic effect is more pronounced in microstructures with larger grains. Thus, damaging processes in the course of extensive t–m transformation are suspected to be intensified during cyclic loading. 相似文献
19.
Naoto Hirosaki Yoshinobu Yamamoto Toshiyuki Nishimura Mamoru Mitomo Junichi Takahashi Hisanori Yamane Masahiko Shimada 《Journal of the American Ceramic Society》2002,85(11):2861-2863
Phase relationships in the Si3 N4 –SiO2 –Lu2 O3 system were investigated at 1850°C in 1 MPa N2 . Only J-phase, Lu4 Si2 O7 N2 (monoclinic, space group P 21 / c , a = 0.74235(8) nm, b = 1.02649(10) nm, c = 1.06595(12) nm, and β= 109.793(6)°) exists as a lutetium silicon oxynitride phase in the Si3 N4 –SiO2 –Lu2 O3 system. The Si3 N4 /Lu2 O3 ratio is 1, corresponding to the M-phase composition, resulted in a mixture of Lu–J-phase, β-Si3 N4 , and a new phase of Lu3 Si5 ON9 , having orthorhombic symmetry, space group Pbcm (No. 57), with a = 0.49361(5) nm, b = 1.60622(16) nm, and c = 1.05143(11) nm. The new phase is best represented in the new Si3 N4 –LuN–Lu2 O3 system. The phase diagram suggests that Lu4 Si2 O7 N2 is an excellent grain-boundary phase of silicon nitride ceramics for high-temperature applications. 相似文献
20.
Compatibility relations of Al2 03 in the quaternary system Zr02-Al2 03 -Si02 -CaO were studied by firing and quenching followed by microscopy and energy-dispersive X-ray examination. A projection of the boundary surface of the primary crystallization volume of Al2 03 was constructed in terms of the CaO, Si02 , and Zr02 contents of the mixtures recalculated to 100 wt%. Two invariant points, where four solids coexist with a liquid phase, are defined, and the positions of the isotherms were established. 相似文献