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1.
Optical observations and X-ray measurements were used to detect the martensitic transformation of tetragonal ZrO2 to the monocline structure during room-temperature stressing of Mg-PSZ. The transformation occurs at stresses as low as ∼200 MPa and is reversible. Additional observations of transformation around Vickers indentations and cracks suggest that application of much higher stresses prevents the reverse transformation on unloading. 相似文献
2.
The monoclinic-tetragonal phase transformation of ZrO2 was examined with a vacuum hot-stage microscope. Polished sections of vacuum-sintered 99.7% pure ZrO2 were observed from room temperature to 1300°C. The rapid formation of platelet substructure within ZrO2 grains in the temperature range 1050° to 1150°C was associated with the heating transformation. Photomicrographs and motion pictures were taken of the specimen as the transformation progressed. The surface deformation was irreversible, preventing observation of the phase inversion on cooling. From these hot-stage studies, supplementary DTA, X-ray, and thermal expansion data, and other existing information, it is concluded that the transformation is of the diffusionless, athermal type, characteristic of Fe-Ni martensitic transformations. 相似文献
3.
The martensitic transformation in tetragonal ZrO2 grains in a ternary MgO-Y2 O3 -ZrO2 alloy has been studied using in situ observations in the transmission electron microscope. Transformation occurred by the nucleation and growth of monoclinic laths; thermoelastic equilibrium can be maintained at different extents of transformation by continuously varying the applied stress. The product phase was always twinned, but two twinning mechanisms were found-sequential formation of twin-related variants and posttransformation deformation twinning. In one example, a (401)/(410) pair of martensite habit planes led to a (100) conjunction twinning plane. 相似文献
4.
The stress-induced martensitic transformation of t -ZrO2 precipitates in a ternary MgO-Y2 O3 -ZrO2 alloy has been studied in situ in the transmission electron microscope. The transformation occurs autocatalytically and takes place by piecewise growth of two twin-related m -ZrO2 variants. Unloading causes retransformation of partially transformed precipitates, but this reverse ( m → t ) transformation of fully transformed precipitates only occurs on heating. The martensitic transformation in this system is clearly thermoelastic . 相似文献
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6.
MICHAEL HOCH 《Journal of the American Ceramic Society》1964,47(12):630-632
The activity of zirconium in the tetragonal ZrO2 phase was measured at 2200° to 2300°K as a function of composition by studying the reaction
From the variation of the zirconium activity with composition, the pairwise interaction energy E11 between vacancies in the oxygen lattice was evaluated at -4.6 ± 1.0 kcal per mole. 相似文献
From the variation of the zirconium activity with composition, the pairwise interaction energy E
7.
An X-ray method to determine the transformation zone size in ceramics containing tetragonal ZrO2 is described. Results obtained on plane fracture surfaces of various composites were correlated to mechanical property data and TEM observations and were found to be in good agreement. This indicates that the method presented is a useful tool for estimating stress-induced transformation zone sizes and for checking the effectiveness of tetragonal particles introduced in a ceramic matrix. 相似文献
8.
Phase changes and the microstructure resulting from low-temperature annealing of yttria-doped tetragonal ZrO2 polycrystals in water were investigated at 65° to 120°C. Tetragonal ZrO2 on the surface of the sintered body transformed to the monoclinic phase, accompanied by microcracking. The transformation rate in water, which was much greater than that in air, was first order with respect to surface concentration of tetragonal ZrO2 . Nonaqueous solvents with a molecular structure containing a lone-pair electron orbital opposite a proton donor site also greatly enhanced the transformation. 相似文献
9.
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
10.
HARRO BESTGEN RACHMAN CHAIM ARTHUR H. HEUER 《Journal of the American Ceramic Society》1988,71(10):826-831
Tetragonal zirconia ( t -ZrO2 ) grains in an annealed ZrO2 8 wt% Y2 O3 alloy transformed to orthorhombic ( o ) or monoclinic ( m ) symmetry by stresses induced by localized electron beam heating in the transmission electron microscope. Different transformation mechanisms were observed, depending on foil thickness and orientation of individual grains. In thicker grains (≥150 nm), the transformation proceeded by a burst-like growth of m laths, and this is believed to approximate bulk behavior. In thinner grains near the edge of the foil, usually those with a [100], orientation perpendicular to the thin-foil surface, "continuous" growth of an o or m phase with an antiphase-boundary-containing microstructure was observed. The o phase is believed to be a high-pressure poly-morph of ZrO2 , which forms (paradoxically) as a thin-foil artifact because it is less dense than t -ZrO2 , but more dense than m -ZrO2 . In some very thin grains, the t → m transformation was thermoelastic. Furthermore, a mottled structure often occurred just before the t → m or t → o transformation, which is attributed to surface transformation. Aside from the lath formation, the observed transformation modes are a result of the reduced constraints in thin foils. 相似文献
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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
13.
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
14.
Fred F. Lange Burt I. Davis Douglas O. Raleigh 《Journal of the American Ceramic Society》1983,66(3):50-C-
The solid sodium electrolyte β"-Al2 O3 (Li-stabilized) was strengthened with additions of tetragonal ZrO2 (15 vol%). The conductivity of this composite material, measured in an Na/Na cell, was 7.7 Ω· at 300°C. Average values of strength and the critical stress intensity factor were 350 MPa and 4.5 MPa·m1/2 , respectively, for the sintered composite material. 相似文献
15.
Fine single-domain and polydomain particles of tetragonal ZrO2 were prepared by hydrothermal and heat treatment of ZrO2 · n H2 O. The particles were characterized by X-ray diffraction, electron microscopy, NMR, mass spectrometry, and ir spectroscopy. The main impurity in the samples was 1 to 2 wt% OH− ions, most of which were concentrated on the particle surfaces or at domain boundaries; some were also distributed in the lattice. Fine single-domain tetragonal particles were strain-free, but polydomain particles had large strains. The single-domain tetragonal particles were transformed much more easily than the polydomain particles by mechanical treatment. The stablization of metastable tetragonal ZrO2 cannot be explained adequately by the surface-energy theory. An explanation based on the concept of a martensitic transformation may be more reasonable. 相似文献
16.
Tetragonal ( t ) ZrO2 precipitates in Mg-, Ca-, and Y-partially-stabilized ZrO2 (Mg-PSZ, Ca-PSZ, Y-PSZ) have different habit planes and different morphologies. These differences arise because of differences in lattice parameters of precipitate and cubic ( c ) ZrO2 matrix in the three systems. The approximate {001} habit plane and oblate spheroid precipitate morphology observed in Mg-PSZ are explained in terms of anisotropic elasticity using the theory of Khachaturyan. The aspect ratio of ∼5 of these particles is used to calculate a c/t interfacial energy of ∼0.15 J·m–2 . The aligned equiaxed precipitates observed in Ca-PSZ and the twinned colonies observed in Y-PSZ can also be explained using this theory and arise from interactions between strain fields during coarsening; the aligned particles in Ca-PSZ may actually represent an intermediate state before the formation of colonies in this system. 相似文献
17.
A. H. HEUER N. CLAUSSEN W.M. KRIVEN M. RUHLE 《Journal of the American Ceramic Society》1982,65(12):642-650
The stability of tetragonal ZrO2 particles in ceramic matrices was considered, with particular reference to Al2 O3 -ZrO2 composites and to partially stabilized ZrO2 . In both systems, particles above a "critical" size transform martensitically to monoclinic symmetry on cooling to room temperature. The critical factors that could affect the size dependence of the transformation temperature—surface and strain energy effects, the chemical free energy driving force, and the difficulty of nucleating the martensitic transformation—were considered. Nucleation arguments are probably the most important. 相似文献
18.
FARHAD K. MOGHADAM TOM YAMASHITA ROBERT SINCLAIR DAVID A. STEVENSON 《Journal of the American Ceramic Society》1983,66(3):213-216
The influence of heat treatment (800°C for 200 h) on the micro-structure of 8 mol% Sc2 O3 -ZrO2 was investigated by XRD and TEM. The starting material was initially characterized and found to contain predominantly cubic-fluorite phase grains, with <5% of the grain containing the rhombohedral β phase. The β phase was positively identified by the analysis of electron diffraction pattern and by quantitative energy dispersive X-ray analysis. On aging, the relative amount of β phase was found to increase to about 15 to 20% by XRD measurement; this was confirmed by TEM observation. The orientation relation between the different variants of the β phase within a grain was determined to be (100)r ||(010)r , and the geometrical arrangement of these variants within the grain was deduced using a 21 /2 D imaging electron microscopy technique. 相似文献
19.
Effect of Densification Conditions on the Stabilization of the Tetragonal Phase in ZrO2 Polycrystals
The stability of the tetragonal phase in tetragonal zirconia polycrystals consolidated at 830 MPa for 2 to 5 s at 1400°C was studied. Consolidation under such conditions stabilizes the tetragonal phase because of the resulting grain size. Subsequent heat treatment of the samples for relatively long periods, however, tends to promote the tetragonal→monoclinic transformation. 相似文献
20.
R. Morena P. E. Lockwood L. Evans C. W. Fairhurst 《Journal of the American Ceramic Society》1986,69(4):75-C-
The effect on mechanical behavior of ZrO2 additions to a dental porcelain was investigated. The ZrO2 was introduced into the glassy matrix phase of the porcelain by refritting the all-glass porcelain constituent. X-ray diffraction indicated that a sizeable fraction of the ZrO2 was retained in the tetragonal form after the porcelain was fired. Zirconia additions to the porcelain produced substantial improvements in fracture toughness, strength, and thermal shock resistance. 相似文献