共查询到20条相似文献,搜索用时 31 毫秒
1.
Paul F. Becher Kathleen B. Alexander Alan Bleier Shirley B. Waters Wilbur H. Warwick 《Journal of the American Ceramic Society》1993,76(3):657-663
Based on experimental and modeling studies, the rate of increase in the martensite start temperature M s for the tetragonal-to-monoclinic transformation with increase in zirconia grain size is found to rise with decrease in ZrO2 content in the zirconia-toughened alumina ZTA system. The observed grain size dependence of M s can be related to the thermal expansion mismatch tensile (internal) stresses which increase with decrease in zirconia content. The result is that finer zirconia grain sizes are required to retain the tetragonal phase as less zirconia is incorporated into the alumina, in agreement with the experimental observations. At the same time, both the predicted and observed applied stress required to induce the transformation are reduced with increase in the ZrO2 grain size. In addition, the transformation-toughening contribution at temperature T increases with increase in the M s temperature brought about by the increase in the ZrO2 grain size, when T > M s . In alumina containing 20 vol% ZrO2 (12 mol% CeO2 ), a toughness of ∼10 MPa. √m can be achieved for a ZrO2 grain size of ∼2 μm ( M s ∼ 225 K). However, at a grain size of ∼2 μm, the alumina–40 vol% ZrO2 (12 mol% CeO2 ) has a toughness of only 8.5 MPa. √m ( M s ∼ 150 K) but reaches 12.3 MPa. ∼m ( M s ∼ 260 K) at a grain size of ∼3 μm. These findings show that composition (and matrix properties) play critical roles in determining the ZrO2 grain size to optimize the transformation toughening in ZrO2 -toughened ceramics. 相似文献
2.
Both tetragonal ( t ) and monoclinic ( m ) ZrO2 particles in ZrO2 -toughened Al2 O3 can give rise to toughening. In the stress field of propagating cracks, the t -ZrO2 particles can undergo the stress-induced t → m transformation, and the residual stresses around already-transformed m -ZrO2 particles can cause microcracking. The t -ZrO2 particles transformed in crack tip stress fields do not, however, also cause appreciable microcracking. The toughening increments via these distinct mechanisms are comparable. It appears that optimally fabricated Zr02 -toughened Al2 O3 's should contain a mixture of t - and m -ZrO2 . 相似文献
3.
Mixtures of ultrafine monoclinic zirconia and aluminum hydroxide were prepared by adding NH4 OH to hydrolyzed zirconia sols containing varied amounts of aluminum sulfate. The mixtures were heat-treated at 500° to 1300°C. The relative stability of monoclinic and tetragonal ZrO2 in these ultrafine particles was studied by X-ray diffractometry. Growth of ZrO2 crystallites at elevated temperatures was strongly inhibited by Al2 O3 derived from aluminum hydroxide. The monoclinic-to-tetragonal phase transformation temperature was lowered to ∼500°C in the mixture containing 10 vol% Al2 O3 , and the tetragonal phase was retained on cooling to room temperature. This behavior may be explained on the basis of Garvie's hypothesis that the surface free energy of tetragonal ZrO2 is lower than that of the monoclinic form. With increasing A12 O3 content, however, the transformation temperature gradually increased, although the growth of ZrO2 particles was inhibited; this was found to be affected by water vapor formed from aluminum hydroxide on heating. The presence of atmospheric water vapor elevates the transformation temperature for ultrafine ZrO2 . The reverse tetragonal-to-monoclinic transformation is promoted by water vapor at lower temperatures. Accordingly, it was concluded that the monoclinic phase in fine ZrO2 particles was stabilized by the presence of water vapor, which probably decreases the surface energy. 相似文献
4.
Francisco del Monte Willa Larsen John D. Mackenzie 《Journal of the American Ceramic Society》2000,83(6):1506-1512
Metastable tetragonal ZrO2 phase has been observed in ZrO2 –SiO2 binary oxides prepared by the sol–gel method. There are many studies concerning the causes of ZrO2 tetragonal stabilization in binary oxides such as Y3 O2 –ZrO2 , MgO–ZrO2 , or CaO–ZrO2 . In these binary oxides, oxygen vacancies cause changes or defects in the ZrO2 lattice parameters, which are responsible for tetragonal stabilization. Since oxygen vacancies are not expected in ZrO2 –SiO2 binary oxides, tetragonal stabilization should just be due to the difficulty of zirconia particles growing in the silica matrix. Furthermore, changes in the tetragonal ZrO2 crystalline lattice parameters of these binary oxides have recently been reported in a previous paper. The changes of the zirconia crystalline lattice parameters must result from the chemical interactions at the silica–zirconia interface (e.g., formation of Si–O–Zr bonds or Si–O− groups). In this paper, FT-IR and 29 Si NMR spectroscopy have been used to elucidate whether the presence of Si–O–Zr or Si–O− is responsible for tetragonal phase stabilization. Moreover, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy have also been used to study the crystalline characteristics of the samples. 相似文献
5.
Glasses of composition 3ZrO2 O · 2SiO2 were prepared by the sol-gel process from metal alkoxides. Tetragonal ZrO2 was precipitated by appropriate heat treatment at 1000° to 1200°C. The fracture toughness of these glass-ceramics increased with increasing crystallite size of the tetragonal ZrO2 , reaching ∼5.0 MN/m3/2 at a size of ∼40 nm. The higher fracture toughness was attributed to tetragonal → monoclinic ZrO2 transformation toughening. 相似文献
6.
Toughening Behavior Involving Multiple Mechanisms: Whisker Reinforcement and Zirconia Toughening 总被引:4,自引:0,他引:4
Since the contribution of transformation toughening increases with the loca crack resistance (which is proportional to the toughness of the matrix), ZrO2 particles were added to a toughened, whisker-reinforced ceramic matrix. Analysis revealed that the combination of these multiple toughening agents should result in ceramic composites tougher than (1) that achieved by either mechanism by itself or (2) the sum of the two processes. The toughness of mullite could be increased 1.8-and 2.4-fold with a 20 vol% addition of ZrO2 particles or SiC whiskers, respectively. However, when 20 vol% of both ZrO2 particles and SiC whiskers were added, the toughness was increased at least 3-fold with monoclinic m -ZrO2 and by >5-fold with tetragonal t -ZrO2 . The differences in the toughening achieved when t -ZrO2 vs m -ZrO2 is present in the SiC-whisker-reinforced mullite are attributed to differences in their interdependencies upon the whisker reinforcement. 相似文献
7.
María C. Caracoche Patricia C. Rivas Mario M. Cervera Ricardo Caruso Edgardo Benavídez Oscar de Sanctis Marta E. Escobar 《Journal of the American Ceramic Society》2000,83(2):377-384
Sol–gel-derived powder samples of zirconia (ZrO2 ) prepared via the dissolution of zirconium n -propoxide in methanol, ethanol, and 2-propanol have been characterized mainly using perturbed angular correlations spectroscopy, as a function of temperature. Results indicate that the nanostructures and subsequent thermal evolution are alcohol dependent: the shorter the alcohol chain, the more hydrolyzed the product. ZrO2 powder that has been obtained using ethanol as the solvent is the product that exhibits the better stabilization of the metastable tetragonal phase ( t -phase). It undergoes a clear and detailed t 1 -form → t 2 -form → monoclinic ZrO2 thermal transformation and shows the highest activation energy against the transformation to the monoclinic phase. 相似文献
8.
The transformation of ultrafine powders (particle size, 0.01 to 0.04 μm) of the system ZrO2– Al2 O3 , prepared by spraying their corresponding nitrate solutions into an inductively coupled plasma (ICP) of ultrahigh temperature, was investigated. The powders were composed of metastable tetragonal ZrO2 ( mt- ZrO2 ) and γ-Al2 O3 . On heating, the mt- ZrO2 (or tetragonal ZrO2 , t -ZrO2 ) was retained up to 1200°C. At 1380°C the transformation to monoclinic ZrO2 ( m -ZrO2 ) occurred and the amount of the m -ZrO2 decreased with the increase in Al2 O3 content, thus indicating the stabilization of the t -ZrO2 by the Al2 O3 , which seems to be explained in terms of the retardation of grain growth. 相似文献
9.
Based on the electrokinetic properties of aqueous silica, boehmite, and ZrO2 dispersions, cordierite-ZrO2 composites were fabricated by a mixed colloidal processing route. The fabricated composite was characterized by a dense and homogeneous microstructure and by a uniform spatial distribution of submicrometer-sized tetragonal ZrO2 particles throughout the matrix. Increasing ZrO2 content enhanced densification and resulted in a full density composite at 20 wt% ZrO2 . Fracture toughness was also increased with increasing ZrO2 content. The enhanced toughening was partly attributed to the martensitic transformation of the dispersed tetragonal ZrO2 particles in a cordierite matrix. The formation of zircon was suppressed by suitably adjusting the heating schedule during sintering. 相似文献
10.
Yu-Seon Shin Young-Woo Rhee Suk-Joong L. Kang 《Journal of the American Ceramic Society》1999,82(5):1229-1232
The contributions of transformation toughening and microcrack toughening in an 85Al2 O3 15ZrO2 (vol%) composite were quantitatively evaluated. Three types of hot-pressed samples with similar size (∼0.5 µm) and size distribution of ZrO2 grains, but with different contents (vol%) of monoclinic- ( m -) ZrO2 (0 (AZS), 45 (AZT), and 67 (AZM)) were prepared using Y2 O3 and MoO2 dopants. Therefore, the possible effect of ZrO2 grain size on each toughening mechanism was eliminated. When the measured fracture toughnesses of m -ZrO2 volume fractions before and after fracture were compared, the transformation-toughening constant was estimated as 3.0 MPam1/2 and the microcrack-toughening constant 0.2 MPam1/2 for a 100% monoclinic transformation of ZrO2 grains. This result indicates that transformation toughening was the dominant toughening mechanism in the studied composite. 相似文献
11.
Several unusual microstructural features, i.e., 90° tetragonal ZrO2 twins containing antiphase domain boundaries, tetragonal ZrO2 precipitates in a colony morphology, and precipitate-free zones at the perimeter of cubic ZrO2 grains containing fine tetragonal ZrO2 precipitates, were observed in a single ZrO2 -12 wt% Y2 O2 ceramic annealed at 1550°, 1400°, and 1250°C, respectively. The type of phase transformation responsible for each microstructural feature is described. 相似文献
12.
SHULIN WEN LITAI MA JINGKUN GUO TUNGSHENG YEN 《Journal of the American Ceramic Society》1986,69(7):570-572
The present work involves the observation of phase transformation in Y2 O3 -containing tetragonal ZrO2 polycrystals (Y-TZP) using electron microscopy. The observations indicate that the martensitic phase transformation ususally starts from grain boundaries. Transformation was also observed at the tip of a microcrack and its adjacent region. Our observations also indicate that the tetragonal ZrO2 grains do not all transform at the same time at the fracture surfaces. 相似文献
13.
Measurement of the Crystallographically Transformed Zone Produced by Fracture in Ceramics Containing Tetragonal Zirconia 总被引:3,自引:0,他引:3
During fracture of ceramics containing tetragonal zirconia particles, a volume of zirconia material on either side of the crack irreversibly transforms to the monoclinic crystal structure. Transformation zone sizes, measured using Raman microprobe spectroscopy, are presented for three sintered ceramics. In a single-phase ZrO2 −3.5 mol% Y2 O3 material, an upper bound measurement of 5 μm is obtained for the zone size. In the Al2 O3 /ZrO2 composites studied, the zone size is deduced to correspond to ∼1 grain in diameter. On the basis of the monoclinic concentrations derived from the Raman spectra it is further concluded that only a fraction of the ZrO2 grains within the transformation zone transform, providing indirect evidence for the effect of particle size on the propensity for transformation. 相似文献
14.
Transformation Toughening in Zirconia-Containing Ceramics 总被引:31,自引:0,他引:31
Richard H. J. Hannink Patrick M. Kelly Barry C. Muddle 《Journal of the American Ceramic Society》2000,83(3):461-487
15.
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
16.
Yttria-ceria-doped tetragonal zirconia (Y,Ce)-TZP)/alumina (Al2 O3 ) composites were fabricated by hot isostatic pressing at 1400° to 1450°C and 196 MPa in an Ar–O2 atmosphere using the fine powders prepared by hydrolysis of ZrOCl2 solution. The composites consisting of 25 wt% Al2 O3 and tetragonal zirconia with compositions 4 mol% YO1.5 –4 mol% CeO2 –ZrO2 and 2.5 mol% YO1.5 –5.5 mol% CeO2 –ZrO2 exhibited mean fracture strength as high as 2000 MPa and were resistant to phase transformation under saturated water vapor pressure at 180°C (1 MPa). Postsintering hot isostatic pressing of (4Y, 4Ce)-TZP/Al2 O3 and (2.5Y, 5.5Ce)-TZP/Al2 O3 composites was useful to enhance the phase stability under hydrothermal conditions and strength. 相似文献
17.
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
18.
Internal Stresses and the Martensite Start Temperature in Alumina-Zirconia Composites: Effects of Composition and Microstructure 总被引:1,自引:0,他引:1
Kathleen B. Alexander Paul F. Becher Xun-Li Wang Chun-Hway Hsueh 《Journal of the American Ceramic Society》1995,78(2):291-296
n alumina-based composites containing ceria-stabilized tetragonal zirconia, the martensite start temperature ( Ms ) of the tetragonal-to-monoclinic zirconia phase transformation exhibits a grain size dependence that becomes increasingly pronounced as the zirconia content decreases. Neutron diffraction experiments confirm earlier dilatometry measurements of M s in composites containing ≥20 vol% ZrO2 and were instrumental in obtaining M s values in lower zirconia content (i.e., 10 vol%) composites. The dependence of M s on zirconia content is related to the internal stresses that arise from differences in thermal expansion coefficients between the two phases. Neutron diffraction measurements show that the internal tensile stresses in the zirconia grains increase with decreasing zirconia content. The measured internal stresses are in quantitative agreement with predictions based on models assuming isolated ZrO2 particles at low zirconia contents and a continuous ZrO2 "matrix" phase at higher zirconia contents. This assumption is consistent with the observed microstructural development in which the low zirconia contents result in isolated zirconia grains, whereas higher zirconia contents result in more interconnected zirconia grains. 相似文献
19.
Ram Srinivasan Burtron H. Davis O. Burl Cavin Camden R. Hubbard 《Journal of the American Ceramic Society》1992,75(5):1217-1222
Amorphous zirconia precursors were made by the precipitation of a zirconium tetrachloride solution with either slow (8 h) or rapid additions of ammonium hydroxide at a pH of 10.5. Following calcination at 500°C for 4 h, the rapidly precipitated precursor exhibited predominantly monoclinic ZrO2 phase, while the slowly precipitated precursor produced the tetragonal ZrO2 phase. The crystallization and phase transformations were followed by in situ high-temperature X-ray diffraction (HTXRD) for both specimens in helium and in air. Each amorphous precursor first crystallizes as the tetragonal phase at about 450°C. A tetragonal-to-monoclinic phase transformation of the rapidly precipitated material was observed on cooling at about 275°C. Surface impregnation of sulfate ions following precipitation inhibited the tetragonal-to-monoclinic transformation for the rapidly precipitated ZrO2 sample. The crystallite size for the t -ZrO2 of all samples, irrespective of whether they transform to monoclinic, was approximately 11 nm, indicating that the t → m transformation in these materials is not controlled by differences in crystallite size. It is therefore suggested that anionic vacancies control the tetragonal-to-monoclinic phase transformation on cooling, and that oxygen adsorption triggers this phase transformation. 相似文献
20.
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