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1.
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
2.
The tetragonal ( t ) and cubic ( c ) ZrO2 solid solutions in two-phase ZrO2 -8 wt% Y2 O3 ceramics have low and high solute content, respectively. Annealing samples sintered at 1600°C between 700° and 1400°C requires a change in the volume fraction of the coexisting phases, as well as their equilibrium Y2 O3 content. The enrichment in Y2 O3 content of the c -ZrO2 grains is accomplished by liquid-film migration involving the ubiquitous silicate grain-boundary phase, while the volume fraction of t -ZrO2 increases by the nucleation and growth of cap-shaped t -ZrO2 lenses. The interfaces between the c -ZrO2 matrix and the growing t -ZrO2 lenses are semicoherent. 相似文献
3.
Conventional ramp-and-hold sintering with a wide range of heating rates was conducted on submicrometer and nanocrystalline ZrO2 –3 mol% Y2 O3 powder compacts. Although rapid heating rates have been reported to produce high density/fine grain size products for many submicrometer and smaller starting powders, the application of this technique to ZrO2 –3 mol% Y2 O3 produced mixed results. In the case of submicrometer ZrO2 –3 mol% Y2 O3 , neither densification nor grain growth was affected by the heating rate used. In the case of nanocrystalline ZrO2 –3 mol% Y2 O3 , fast heating rates severely retarded densiflcation and had a minimal effect on grain growth. The large adverse effect of fast heating rates on the densification of the nanocrystalline powder was traced to a thermal gradient/differential densification effect. Microstructural evidence suggests that the rate of densification greatly exceeded the rate of heat transfer in this material; consequently, the sample interior was not able to densify before being geometrically constrained by a fully dense shell which formed at the sample exterior. This finding implies that rapid rate sintering will meet severe practical constraints in the manufacture of bulk nanocrystalline ZrO2 –3 mol% Y2 O3 specimens. 相似文献
4.
J. LLorca José Y. Pastor Pedro Poza José I. Peña Isabel de Francisco Angel Larrea Victor M. Orera 《Journal of the American Ceramic Society》2004,87(4):633-639
The effect of Y2 O3 content on the flexure strength of melt-grown Al2 O3 –ZrO2 eutectics was studied in a temperature range of 25°–1427°C. The processing conditions were carefully controlled to obtain a constant microstructure independent of Y2 O3 content. The rod microstructure was made up of alternating bands of fine and coarse dispersions of irregular ZrO2 platelets oriented along the growth axis and embedded in the continuous Al2 O3 matrix. The highest flexure strength at ambient temperature was found in the material with 3 mol% Y2 O3 in relation to ZrO2 (Y2 O3 ). Higher Y2 O3 content did not substantially modify the mechanical response; however, materials with 0.5 mol% presented a significant degradation in the flexure strength because of the presence of large defects. They were nucleated at the Al2 O3 –ZrO2 interface during the martensitic transformation of ZrO2 on cooling and propagated into the Al2 O3 matrix driven by the tensile residual stresses generated by the transformation. The material with 3 mol% Y2 O3 retained 80% of the flexure strength at 1427°C, whereas the mechanical properties of the eutectic with 0.5 mol% Y2 O3 dropped rapidly with temperature as a result of extensive microcracking. 相似文献
5.
Effect of Ta2 O5 , Nb2 O5 , and HfO2 Alloying on the Transformability of Y2 O3 -Stabilized Tetragonal ZrO2
Dae-Joon Kim 《Journal of the American Ceramic Society》1990,73(1):115-120
The addition of Ta2 O5 , Nb2 O5 , and HfO2 enhanced the transformability of Y2 O3 -stabilized tetragonal ZrO2 polycrystal (Y-TZP), which was indicated by an increase in phase transformation temperatures and fracture toughness of Y-TZP. Comparison of the alloying effects of these oxides on the transformability and crystal structure of Y-TZP suggested that an alloying oxide which increases the c/a axial ratio (tetragonality) of TZP also increases the transformability. Empirical equations to predict the tetragonality are proposed. Calculated tetragonalities showed good agreement with measured values in the systems ZrO2 -Y2 O3 -Ta2 O5 , -Nb2 O5 , and -HfO2 . 相似文献
6.
Masahiro Yoshimura Manikpurage Jayaratna Shigeyuki Smiya 《Journal of the American Ceramic Society》1982,65(10):c166-c168
The pseudoternary system ZrO2 -Y2 O3 -Cr2 O3 was studied at 1600°C in air by the quenching method. Only one intermediate compound, YCrO3 , was observed on the Y2 O3 −Cr2 O3 join. ZrO2 and Y2 O3 formed solid solutions with solubility limits of 47 and 38 mol%, respectively. The apex of the compatibility triangle for the cubic ZrO2 , Cr2 O3 , and YCrO3 three-phase region was located at =17 mol% Y2 O3 (83 mol% ZrO2 ). Below 17 mol% Y2 O3 , ZrO2 solid solution coexisted with Cr2 O3 . Cr2 O3 appears to be slightly soluble in ZrO2 (ss). 相似文献
7.
The subsolidus phase relations in the entire system ZrO2 -Y2 O3 were established using DTA, expansion measurements, and room- and high-temperature X-ray diffraction. Three eutectoid reactions were found in the system: ( a ) tetragonal zirconia solid solution→monoclinic zirconia solid solution+cubic zirconia solid solution at 4.5 mol% Y2 O3 and ∼490°C, ( b ) cubic zirconia solid solutiow→δ-phase Y4 Zr3 O12 +hexagonalphase Y6 ZrO11 at 45 mol% Y2 O3 and ∼1325°±25°C, and ( c ) yttria C -type solid solution→wcubic zirconia solid solution+ hexagonal phase Y6 ZrO11 at ∼72 mol% Y2 O3 and 1650°±50°C. Two ordered phases were also found in the system, one at 40 mol% Y2 O3 with ideal formula Y4 Zr3 O12 , and another, a new hexagonal phase, at 75 mol% Y2 O3 with formula Y6 ZrO11 . They decompose at 1375° and >1750°C into cubic zirconia solid solution and yttria C -type solid solution, respectively. The extent of the cubic zirconia and yttria C -type solid solution fields was also redetermined. By incorporating the known tetragonal-cubic zirconia transition temperature and the liquidus temperatures in the system, a new tentative phase diagram is given for the system ZrO2 -Y2 O3 . 相似文献
8.
Shingo Hirano Masaru Yoshinaka Ken Hirota Osamu Yamaguchi 《Journal of the American Ceramic Society》1996,79(1):171-176
In the ZrO2 -Cr2 O3 system, metastable t -ZrO2 solid solutions containing up to 11 mol% Cr2 O3 crystallize at low temperatures from amorphous materials prepared by the hydrazine method. The lattice parameter c decreases linearly from 0.5149 to 0.5077 nm with increased Cr2 O3 content, whereas the lattice parameter a is a constant value ( a = 0.5077 nm) regardless of the starting composition. At higher temperatures, transformation (decomposition) of the solid solutions proceeds in the following way: t (ss)→ t (ss) + m + Cr2 O3 → m + Cr2 O3 . Above 11 mol% Cr2 O3 addition, c-ZrO2 phases are formed in the presence of Cr2 O3 . The t -ZrO2 solid solution powders have been characterized for particle size, shape, and surface area. They consist of very fine particles (15–30 nm) showing thin platelike morphology. Dense ZrO2 (3Y)-Cr2 O3 composite ceramics (∼99.7% of theoretical) with an average grain size of 0.3 μm have been fabricated by hot isostatic pressing for 2 h at 1400°C and 196 MPa. Their fracture toughness increases with increased Cr2 O3 content. The highest K Ic value of 9.5 MPa·;m1/2 is achieved in the composite ceramics containing 10 mol% Cr2 O3 . 相似文献
9.
Jin-Ho Lee Masatomo Yashima Masato Kakihana Masahiro Yoshimura 《Journal of the American Ceramic Society》1998,81(4):894-900
The phase equilibria in the Y2 O3 -Nb2 O5 system have been studied at temperatures of 1500° and 1700°C in the compositional region of 0-50 mol% Nb2 O5 . The solubility limits of the C-type Y2 O3 cubic phase and the YNbO4 monoclinic phase are 2.5 (±1.0) mol% Nb2 O5 and 0.2 (±0.4) mol% Y2 O3 , respectively, at 1700°C. The fluorite (F) single phase exists in the region of 20.1-27.7 mol% Nb2 O5 at 1700°C, and in the region of 21.1-27.0 mol% Nb2 O5 at 1500°C, respectively. Conductivity of the Y2 O3 - x mol% Nb2 O5 system increases as the value of x increases, to a maximum at x = 20 in the compositional region of 0 ≤ x ≤ 20, as a result of the increase in the fraction of F phase. In the F single-phase region, the conductivity decreases in the region of 20-25 mol% Nb2 O5 , because of the decrease in the content of oxygen vacancies, whereas the conductivity at x = 27 is larger than that at x = 25. The conductivity decreases as the value of x increases in the region of 27.5 ≤ x ≤ 50, because of the decrease in the fraction of F. The 20 mol% Nb2 O5 sample exhibits the highest conductivity and a very wide range of ionic domain, at least up to log p O 2 =−20 (where p O 2 is given in units of atm), which indicates practical usefulness as an ionic conductor. 相似文献
10.
Jonathan D. French Helcn M. Chan Martin P. Harmer Gary A. Miller 《Journal of the American Ceramic Society》1992,75(2):418-423
Composites of Al2 O3 (A) and cubic ZrO2 (Z) (8 mol% Y2 O3 ) (with c -ZrO2 volume fractions ranging from O to 1) were fabricated by pressureless sintering of mechanically mixed powders. The microstructures of the AZ composites were duplex, with the grains of both phases exhibiting similar size. Room-temperature mechanical properties including Young's modulus (determined from elastic wave velocity measurements), strength and toughness (by indentation-strength-in-bending), and Vickers microhardness were evaluated for the full range of compositions. All properties exhibited a linear decrease with increasing c -ZrO2 content, and no R -curve behavior was seen in any of the composite compositions. Fracture morphology, observed from cracks emanating from microhardness indentations, changed from essentially intergranular for the tougher Al2 O3 to transgranular for c -ZrO2 , with AZ composites exhibiting mixed morphology. 相似文献
11.
Osamu Yokota Masatomo Yashima Naoki Yamamoto Masahiro Yoshimura 《Journal of the American Ceramic Society》1997,80(9):2429-2432
Melts of x mol% Ta2 O5 –Y2 O3 (x = 0–32.5) were rapidly quenched to investigate the formation of metastable fluorite solid solutions. C-type Y2 O3 , fluorite, and fergusonite phases existed in the compositional regions of 0 x 16, 8 x 32.5, and 27.5 x 32.5, respectively. Their lattice parameters were precisely measured through either Rietveld analysis or a least-squares fit of the individual X-ray diffraction peak positions. The lattice parameter of the fluorite phase decreased linearly with increasing Ta2 O5 content, strongly suggesting the formation of compositionally homogeneous metastable solid solutions. Ta2 O5 was almost insoluble into Y2 O3 at 1700°C in the equilibrium state. 相似文献
12.
Ehrenfried Zschech Paris N. Kountouros Günter Petzow Peter Behrens Alex Lessmann Ronald Frahm 《Journal of the American Ceramic Society》1993,76(1):197-201
Valence state and site symmetry of Ti ions in TiO2 –Y2 O3 –ZrO2 powders with 2 mol% Y2 O3 and 5, 10, 15, and 20 mol% TiO2 , respectively, are studied by X-ray absorption near-edge spectroscopy (XANES). Tetravalent Zr4+ ions are replaced predominantly by Ti4+ ions. Within the solubility region of Ti ions, a subsequent displacement of Ti ions from the center of symmetry is observed with increasing TiO2 content in TiO2 –Y2 O3 -stabilized tetragonal ZrO2 polycrystals (Ti-Y-TZP) under investigation. This behavior cannot be interpreted with a random substitution of Ti4+ ions on Zr4+ lattice sites. On the contrary, this correlation between the TiO2 content in Ti-Y-TZP and the shift of Ti ions indicates an increasing interaction between the Ti ions with growing TiO2 content, caused by a subsequent clustering of Ti ions. 相似文献
13.
Kentaro Fukuda Teiichi Hanada Setsuhisa Tanabe Takeshi Yao 《Journal of the American Ceramic Society》2002,85(4):915-920
Amorphous films in the system Al2 O3 –Y2 O3 were prepared by the rf sputtering method in the range of 0–76 mol% Y2 O3 , and their density, refractive index, and elastic constants were measured. All of the physical properties of the amorphous Al2 O3 –Y2 O3 films had a similar compositional dependence; that is, they increased continuously, but not linearly with increasing Y2 O3 content. To confirm the coordination states of aluminum and yttrium ions in the amorphous Al2 O3 –Y2 O3 films, the Al K α X-ray emission spectra and the X-ray absorption near edge structures (XANES) were measured. The average coordination number of aluminum ions in the amorphous films containing up to about 40 mol% Y2 O3 content was 5, that is a mixture of 4-fold- and 6-fold-coordinated states. In the region of more than about 50 mol% Y2 O3 , the fraction of the 6-fold-coordinated aluminum ions increased with increasing Y2 O3 content, while the results led to the conclusion that the coordination number of yttrium ions was always 6, regardless of composition. These results indicate that, in amorphous films in the system Al2 O3 –Y2 O3 , the change of the coordination state of aluminum ions has an important effect on physical properties. 相似文献
14.
The phase diagram for the system ZrO2 -Y2 O3 was redetermined. The extent of the fluorite-type ZrO2 -Yz O3 solid solution field was determined with a high-temperature X-ray furnace, precise lattice parameter measurements, and a hydrothermal technique. Long range ordering occurred at 40 mol% Y2 O3 and the corresponding ordered phase was Zr3 Y4 OL12 . The compound has rhombohedra1 symmetry (space group R 3), is isostructural with UY6 Ol2 and decomposes above 1250±50°C. The results indicate that the eutectoid may occur at a temperature <400°C at a composition between 20 and 30 mol% Y2 O3 Determination of the liquidus line indicated a eutectic at 83± 1 mol% Y2 O3 and a peritectic at 76 ± 1 mol% Y2 O3 . 相似文献
15.
Xinzhang Zhou Vijay Shukla W. Roger Cannon Bernard H. Kear 《Journal of the American Ceramic Society》2003,86(8):1415-1420
Rapidly solidified ZrO2 (Y2 O3 )–Al2 O3 powders were prepared by melting fine-particle aggregates in a high-enthalpy plasma flame and then rapidly quenching them in cold water or on a copper chill plate. To ensure complete melting and homogenization of all the particles before quenching, the water-quenching treatment was often repeated two or even three times. The resulting melt-quenched powders and splats displayed a variety of metastable structures, depending on composition and cooling rate. ZrO2 -rich material developed an extended solid solution phase, whereas eutectic material formed a nanofibrous or amorphous structure. Under high cooling rate conditions, the ZrO2 -rich material developed a nanocomposite structure ( t -ZrO2 +α-Al2 O) directly by melt-quenching, whereas, more typically, such a structure was developed only after postannealing of the as-quenched metastable material. 相似文献
16.
The crystallization of MgO-Al2 O3 -SiO2 -ZrO2 glasses at 1000°C was studied. Isothermal heat treatments of a cordierite-based glass (2MgO.2Al2 O3 .5SiO2 = Mg2 Al4 Si5 O18 ) with 7 wt% ZrO2 produced surface crystallization of α-cordierite and tetragonal ZrO2 ( t -ZrO2 ). These phases advanced into the glass by cocrystallization of t -ZrO2 rods in an α-cordierite matrix with a well-defined orientation relation. The t -ZrO2 rods were unstable with respect to diffusional breakup (a Rayleigh instability) and decomposed into rows of aligned ellipsoidal and spheroidal particles. The t -ZrO2 was very resistant to transformation to monoclinic symmetry. With a similar glass containing 15 wt% ZrO2 , surface crystallization of α-cordierite and t -ZrO2 was accompanied by internal crystallization of t -ZrO2 dendrites. Transformation of the dendrites to mono-clinic symmetry was observed under some conditions. 相似文献
17.
Kazunari Sasaki Petr Bohac Ludwig J. Gauckler 《Journal of the American Ceramic Society》1993,76(3):689-698
Phase equilibria in the system ZrO2 ─InO1.5 have been investigated in the temperature range from 800° to 1700°C Up to 4 mol%, InO1.5 is soluble in t -ZrO2 at 1500°C. The martensitic transformation temperature m → t of ZrO2 containing InO1.5 is compared with that of ZrO2 solid solutions with various other trivalent ions with different ionic radii. The diffusionless c → t ' A phase transformation is discussed. Extended solid solubility from 12.4 ± 0.8 to 56.5 ± 3 mol% InO1.5 is found at 1700°C in the cubic ZrO2 phase. The eutectoid composition and temperature for the decomposition of c -ZrO2 solid solution into t -ZrO2 +InO1.5 solid solutions were determined. A maximum of about 1 mol% ZrO2 is soluble in bcc InO1.5 phase. Metastable supersaturation of ZrO2 in bcc InO 1.5 and conditions for phase separation are discussed. 相似文献
18.
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
19.
The phase relations for the system y2 o3 –Ta2 o5 in the composition range 50 to 100 mol% Y2 O3 have been studied by solid-state reactions at 1350°, 1500°, or 17000C and by thermal analyses up to the melting temperatures. Weberite-type orthorhombic phases (W2 phase, space group C2221 ), fluorite-type cubic phases (F phase, space group Fm3m )and another orthorhombic phase (O phase, space group Cmmm )are found in the system. The W2 phase forms in 75 mol% Y2 O3 under 17000C and O phase in 70 mol% Y2 O3 up to 1700°C These phases seem to melt incongruently. The F phase forms in about 80 mol% Y2 O3 and melts congruently at 2454° 3°C. Two eutectic points seem to exist at about 2220°C 90 mol% Y2 O3 , and at about 1990°C, 62 mol% Y2 O3 . A Phase diagram including the above three phases were not identified with each other. 相似文献
20.
Osamu Yamaguchi Daijo Tomihisa Masakazu Shirai Kiyoshi Shimizu 《Journal of the American Ceramic Society》1988,71(5):260-C
In the system Nb2 O5 –Ta2 O5 , a continuous series of δ-Nb2 O5 (δ-Ta2 O5 ) solid solutions with a hexagonal cell is formed while heating amorphous materials prepared by the simultaneous hydrolysis of niobium and tantalum alkoxides. The lattice parameters a and c change linearly with increasing Ta2 O5 content; the former value increases from 0.3604 to 0.3620 nm, and the latter value decreases from 0.3923 to 0.3883 nm. They transform to γ-Nb2 O5 (β-Ta2 O5 ) solid solutions with an orthorhombic cell at higher temperatures. The changes in lattice parameters a and c as functions of composition are the same as those of hexagonal solid solutions, whereas parameter b is relatively constant. 相似文献