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1.
Petra A. Langjahr Rainer Oberacker Michael J. Hoffmann 《Journal of the American Ceramic Society》2001,84(6):1301-1308
Investigations of changes in phase composition, mechanical properties, and microstructure of ZrO2 -based plasma-sprayed thermal barrier coatings (TBCs) with 8 mol% CeO2 , 19.5 mol% CeO2 /1.5 mol% Y2 O3 , 35 mol% CeO2 , and 4.5 mol% Y2 O3 after long-term heat treatments at typical operation temperatures (1000°–1400°C) are presented. Experimental studies include X-ray diffractometry, mechanical testing, and scanning electron microscopy. Thermal cycling experiments also have been performed. TBCs with 8 mol% CeO2 contain mainly the tetragonal equilibrium phase and, therefore, show rapid failure because of the high amount of tetragonal → monoclinic phase transformation, even after relatively short heat treatments (1250°C/1 h). In the case of the other systems that consist mainly of the tetragonal or cubic nonequilibrium phases, TBCs with 19.5 mol% CeO2 /1.5 mol% Y2 O3 or 35 mol% CeO2 reveal a smaller amount of monoclinic phase after long-term heat treatments (1250°C/1000 h) compared with TBCs containing 4.5 mol% Y2 O3 . TBCs containing 35 mol% CeO2 show a higher degree of sintering than the TBCs with 19.5 mol% CeO2 /1.5 mol% Y2 O3 and, therefore, a greater increase of the elastic modulus. Among the systems investigated, TBCs containing 4.5 mol% Y2 O3 exhibit the highest resistance to failure in thermal-cycling experiments. 相似文献
2.
The phase equilibria in the zirconia-rich part of the system ZrO2 −Yb2 O3 −Y2 O3 were determined at 1200°, 1400°, and 1650°C. The stabilizing effects of Yb2 O3 and Y2 O3 were found to be quite similar with <10 mol% of either being necessary to fully stabilize the cubic fluorite-structure phase at 1200°C. The two binary ordered phases, Zr3 Yb4 O12 and Zr3 Y4 O12 , are completely miscible at 1200°C. These were the only binary or ternary phases detected. The ionic conductivities of ternary specimens in this system were measured using the complex impedance analysis technique. For a given level of total dopant, the substitution of Yb2 O3 for Y2 O3 gives only minor increases in specimen conductivity. 相似文献
3.
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
4.
Phase Formation and Stability in Reactively Sputter Deposited Yttria-Stabilized Zirconia Coatings 总被引:1,自引:0,他引:1
Zhiqiang Ji J. Allen Haynes Edgar Voelkl J. Michael Rigsbee 《Journal of the American Ceramic Society》2001,84(5):929-936
Yttria-stabilized zirconia (YSZ) coatings were produced by reactively cosputtering metallic zirconium and yttrium targets in an argon and oxygen plasma using a system with multiple magnetron sputtering sources. Coating crystal structure and phase stability, as functions of Y2 O3 content, substrate bias, and annealing temperature, were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results demonstrated that highly (111)-oriented tetragonal and cubic zirconia structures were formed in 2 and 4.5 mol% Y2 O3 coatings, respectively, when the coatings were grown with an applied substrate bias. Conversely, coatings deposited with no substrate bias had random tetragonal and cubic structures. XRD analysis of annealed coatings showed that the cubic zirconia in 4.5 mol% Y2 O3 coatings exhibited structural stability at temperatures up to 1200°C. Transformation of the tetragonal to monoclinic phase occurred in 2 mol% Y2 O3 coating during high-temperature annealing, with the fraction of transformation dependent on bias potential and annealing temperature. 相似文献
5.
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
6.
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
7.
C. E. CURTIS 《Journal of the American Ceramic Society》1957,40(8):274-278
The cubic structure of yttrium oxide is stable to 1800°C. in air as indicated by petrographic, X-ray, and differential thermal analyses. A change in lattice parameter of less than ±0.007 a.u. was observed on heating the oxide to 1800°C. The mean specific heat of Y2 O3 to 1600°C. was 0.13 cal. per gm. per °C. The coefficient of linear expansion to 1400°C. was 9.3 × 10−6 in. per in. per °C. Compacts of Y2 O3 required a temperature of 1800°C. for vitrification. In equimolecular binary mixtures heated in the powdered state at 1500°C., Y2 O3 formed compounds with Al2 O3 and Fe2 O3 and solid solutions with ZrO2 and HfO2 . Y2 O3 did not react with CaO, MgO, or ThO2 . Crystal types and unit-cell sizes of the reaction products are included. 相似文献
8.
Young-Hag Koh Hae-Won Kim Hyoun-Ee Kim John W. Halloran 《Journal of the American Ceramic Society》2002,85(12):3123-3125
The oxidation behavior and its effect on the mechanical properties of fibrous monolith Si3 N4 /BN after exposure to air at temperatures ranging from 1000° to 1400°C for up to 20 h were investigated. After exposure at 1000°C, only the BN cell boundary was oxidized, forming a B2 O3 liquid phase. With increasing exposure temperature, the Si3 N4 cells began to oxidize, forming crystalline Y2 Si2 O7 , SiO2 , and silicate glass. However, in this case, a weight loss was observed due to extensive vaporization of the B2 O3 liquid. After exposure at 1400°C, large Y2 Si2 O7 crystals with a glassy phase formed near the BN cell boundaries. The oxidation behavior significantly affected the mechanical properties of the fibrous monolith. The flexural strength and work-of-fracture decreased with increasing exposure temperature, while the noncatastrophic failure was maintained. 相似文献
9.
A novel and cost-effective electrostatic spray-assisted vapor deposition (ESAVD) was used to deposit Y3 Al5 O12 (YAG) coatings. Polycrystalline single-phase Y3 Al5 O12 coatings were synthesized using the ESAVD method in an open atmosphere at 650°C, and then annealed at 700°–900°C for 1 h. The ESAVD process involves the decomposition and chemical reactions of charged aerosol in vapor phase. The low-temperature coating deposition characteristics of the ESAVD process using a suitable sol precursor decreases the reaction and crystallization temperatures for forming Y3 Al5 O12 coatings. The microstructure of the Y3 Al5 O12 coating prepared using the ESAVD method is columnar and such strain-resistance microstructure could be useful for thermal barrier coating applications. 相似文献
10.
Jean-Pierre Lawanier James K. Meen Don Elthon 《Journal of the American Ceramic Society》1996,79(2):533-535
Phase equilibria in the YO1.5 BaO-CuO system have been determined at 950°C at 10 kbar using a piston-cylinder apparatus. The oxide phases stable under these conditions are Y2 O3 , Y2 Cu2 O5 , CuO, Y2 BaCuO5 , YBa2 Cu3 O6.5 , BaCuO2 , Y2 BaO4 , Y2 Ba3 O6 , and YBa4 Cu2 O7.5 . The phase stabilities observed at 950°C at 10 kbar are identical to those observed at 950°C in air or oxygen at 1 atm for compositions with <40% Ba of the cations. In more Ba-rich portions of the phase diagram, carbonates and oxycarbonates are stabilized and a systematic determination of the phase equilibria has not been successful. 相似文献
11.
Kuan Zong Fung Anil V. Virkar David L. Drobeck 《Journal of the American Ceramic Society》1994,77(6):1638-1648
Cubic solid solutions in the Y2 O3 -Bi2 O3 system with ∼25% Y2 O3 undergo a transformation to a rhombohedral phase when annealed at temperatures ≤ 700°C. This transformation is composition-invariant and is thermally activated, and the product phase can propagate across matrix grain boundaries, indicating that there is no special crystallo-graphic orientation relationship between the product and the parent phases. Based on these observations, it is proposed that cubic → rhombohedral phase transformation in the Y2 O3 -Bi2 O3 system is a massive transformation. Samples of composition 25% Y2 O3 -75% Bi2 O3 with and without aliovalent dopants were annealed at temperatures ≤ 700°C for up to 10000 h. ZrO2 as a dopant suppressed while CaO and SrO as dopants enhanced the kinetics of phase transformation. The rate of cubic/rhombohedra1 interface migration (growth rate or interface velocity) was also similarly affected by the additions of dopants; ZrO2 suppressed while CaO enhanced the growth rate. Diffusion studies further showed that ZrO2 suppressed while CaO enhanced cation interdiffusion coefficient. These observations are rationalized on the premise that cation interstitials are more mobile compared to cation vacancies in cubic bismuth oxide. The maximum growth rate measured was ∼10−10 m/s, which is orders of magnitude smaller than typical growth rates measured in metallic alloys. This difference is explained in terms of substantially lower diffusion coefficients in these oxide systems compared to metallic alloys. 相似文献
12.
JENQ-GONG DUH HSING-TAO DAI BI-SHIOU CHIOU 《Journal of the American Ceramic Society》1988,71(10):813-819
A wet-chemical approach is applied to derive fine powders with compositions 11 mol% CeO2 -ZrO2 , 1 mol% YO1.5 -10 mol% CeO2 -ZrO2 , 12 mol% CeO2 -ZrO2 , and 2 mol% YO1.5 -10 mol% CeO2 -ZrO2 by the coprecipitation method. The characteristics of the as-derived powders are evaluated through thermal analysis and electron microscopy. The sintering behavior of the calcined powders is carried out at 1400° and 1500°C for 1 to 10 h. Sintered density higher than 98% of theoretical is achieved for sintering at 1400°C for several hours. The as-sintered density dependence on the sintering condition is related to the extent of tetragonal-to-monoclinic phase transformation as well as the associated microcracks. Partial substitution by Y2 O3 in CeO2 -ZrO2 results in reduced grain size and tends to stabilize the tetragonal structure. Y2 O3 is more effective than CeO2 with respect to the grain size refinement and tetragonal stability. In addition, Y2 O3 substitution in CeO2 -ZrO2 increases the hardness, while it decreases the fracture toughness. 相似文献
13.
Hot isostatic pressing was studied for densification of reaction-bonded Si3 N4 containing various levels of Y2 O3 . Near-theoretical density was achieved for com positions containing 3 to 7 wt% Y2 O3 . An Si3 N4 -5 wt% Y2 O3 composition had a 4-point flexural strength at 1375°C of 628 MPa and survived 117 h of stress rupture testing at 1400°C and 345 MPa . 相似文献
14.
Shuigen Huang Omer Van der Biest Jef Vleugels Lin Li 《Journal of the American Ceramic Society》2006,89(8):2596-2601
The phase relations in the Nd2 O3 –Y2 O3 system were experimentally studied in the 1300°–1600°C range. X-ray diffraction, scanning electron microscopy, and electron probe microanalysis were applied to analyze the phase composition of annealed Nd2 O3 –Y2 O3 mixtures with varying Y2 O3 content. A thermodynamic assessment was conducted using the experimental data obtained. The excess Gibbs energies of the solution phases were described based on a simple substitutional solution model. A consistent set of optimized interaction parameters was derived for the Gibbs energy of the constituent phases, resulting in a good match between calculated and experimental data. 相似文献
15.
V. A. Izhevskyi A. H. A. Bressiani J. C. Bressiani 《Journal of the American Ceramic Society》2005,88(5):1115-1121
A series of silicon carbide-based ceramics with different sintering additives were liquid-phase sintered to high densities. Yb2 O3 in combination with AlN was used as the additive, instead of the commonly used Y2 O3 –AlN, to improve the refractoriness of the secondary phase. Thermo-chemical decomposition of AlN was sufficiently suppressed with the use of nitrogen overpressure and reasonable weight loss was achieved in the different additive containing SiC ceramics without a reactive powder bed. Use of the heavier rare-earth element modified the liquid phase formed during sintering and reduced the phase transformation controlled grain growth rate, compared with Y2 O3 doped materials. It also permitted microstructure tailoring through post-sintering heat treatments in nitrogen. Materials with self-reinforced microstructures, formed as a result of anisotropic grain growth, were obtained. Improved fracture toughness (4.5–5 MPa/m1/2 ) and good flexural strength retention up to 1400°C were also observed. 相似文献
16.
A tracer sectioning technique was used to measure cation self-diffusion coefficients in fully dense polycrystalline Ya O3 and Er2 Os under oxidizing conditions. The results are described by the relations for Y2 O3 (1400° to 1670°C), and for Er2 O3 (1400° to 1700°C). The greater activation energy for erbium diffusion in erbia may be partly attributable to a mass effect. 相似文献
17.
ZrO2 -2 mol% Y2 O3 crystals with average grain sizes from 0.51 to 0.96 µm were prepared by sintering in air at 1400°C for 2 to 100 h. The tetragonal-to-monoclinic phase transformation associated with the low-temperature degradation was investigated to clarify how the presence of water directly affects the influence of grain size on transformation. The specimens were exposed to water at 80–120°C, a temperature range in which transformation by thermal activation is difficult in the absence of water. Contrary to expectations, this type of low-temperature transformation did not accelerate monotonously with increasing grain size. Instead, the amount of phase transformation first decreased, reaching a constant value, and then increased with increasing grain size. Such interesting results can be explained satisfactorily by the combined influences of grain size on the nucleation process, because of preferential dissolution of yttrium at the grain boundaries, and the intrinsic transformability of Y2 O3 -doped tetragonal ZrO2 grains. 相似文献
18.
Eric L. Brosha † Fernando H. Garzon Ian D. Raistrick Peter K. Davies 《Journal of the American Ceramic Society》1995,78(7):1745-1752
Ultrasonically prepared freeze-dried nitrate precursors and high-precision solution calorimetry were used to investigate the low-temperature thermodynamic stabilities of compounds in the Y-Cu-O, Ba-Cu-O, Y-Ba-O, and Y-Ba-Cu-O pseudobinary and pseudoternary systems at 1 atm of oxygen. Y2 Cu2 O5 , Y2 BaCuOs , and BaCuO2 were found to be metastable below 682°, 728°, and 710°± 5°C, respectively. The only stable phases in the Y-Ba-Cu-O system at 298 K and 1 atm of oxygen are Ba2 Cu3 O6 , CuO, BaO2 , and Y2 O3 . By compiling the calorimetric and phase equilibria data, a series of Y-Ba-Cu-O isothermal phase diagrams were constructed between 25° and 900°C at 1 atm of oxygen. 相似文献
19.
Heon-Jin Choi June-Gunn Lee Young-Wook Kim 《Journal of the American Ceramic Society》2002,85(9):2281-2286
Silicon carbide (SiC) ceramics have been fabricated by hot-pressing and subsequent annealing under pressure with aluminum nitride (AlN) and rare-earth oxides (Y2 O3 , Er2 O3 , and Yb2 O3 ) as sintering additives. The oxidation behavior of the SiC ceramics in air was characterized and compared with that of the SiC ceramics with yttrium–aluminum–garnet (YAG) and Al2 O3 –Y2 O3 –CaO (AYC). All SiC ceramics investigated herein showed a parabolic weight gain with oxidation time at 1400°C. The SiC ceramics sintered with AlN and rare-earth oxides showed superior oxidation resistance to those with YAG and Al2 O3 –Y2 O3 –CaO. SiC ceramics with AlN and Yb2 O3 showed the best oxidation resistance of 0.4748 mg/cm2 after oxidation at 1400°C for 192 h. The minimization of aluminum in the sintering additives was postulated as the prime factor contributing to the superior oxidation resistance of the resulting ceramics. A small cationic radius of rare-earth oxides, dissolution of nitrogen to the intergranular glassy film, and formation of disilicate crystalline phase as an oxidation product could also contribute to the superior oxidation resistance. 相似文献
20.
ROBERT RUH K. S. MAZDIYASNI P. G. VALENTINE H. O. BIELSTEIN 《Journal of the American Ceramic Society》1984,67(9):190-C
Subsolidus phase relations in the low-Y2 O3 portion of the system ZrO2- Y2 O3 were studied using DTA with fired samples and X-ray phase identification and lattice parameter techniques with quenched samples. Approximately 1.5% Y2 O3 is soluble in monoclinic ZrO2 , a two-phase monoclinic solid solution plus cubic solid solution region exists to ∼7.5% Y2 O3 below ∼500°C, and a two-phase tetragonal solid solution plus cubic solid solution exists from ∼1.5 to 7.5% Y2 O3 from ∼500° to ∼1600°C. At higher Y2 O3 compositions, cubic ZrO2 solid solution occurs. 相似文献