共查询到20条相似文献,搜索用时 15 毫秒
1.
Bo-Chen Wu Edward Chang Shih-Feng Chang David Tu 《Journal of the American Ceramic Society》1989,72(2):212-218
Duplex ZrO2 –8 wt% Y2 O3 /Ni-22Cr-10Al-1Y thermal barrier coatings (TBCs) on Mar-M247 superalloy were tested under different operating conditions within the temperature range 1000° to 1150°C. Results of experiments in this study show that oxidation of bond coatings is the dominant TBC degradation mechanism whereas the operationally induced stresses exert a conjugate effect. The mechanisms of sintering and phase transformation of top coatings do not contribute to failure of TBCs within the temperature range studied. NiO and Ni(Cr,Al)2 O4 grown on the surfaces of the bond coatings seem to accelerate spalling of the top coatings along a top coating/bond coating out-grown oxide interface. However, it is also concluded that the lifetime of TBCs is not directly related to a critical specific weight gain under thermal cycling conditions. 相似文献
2.
Sung R. Choi Dongming Zhu Robert A. Miller 《International Journal of Applied Ceramic Technology》2004,1(4):330-342
Mechanical behavior of free-standing, plasma-sprayed ZrO2 -8wt% Y2 O3 thermal barrier coatings, including strength, fracture toughness, fatigue, constitutive relation, elastic modulus, and directionality, have been determined under various loading-specimen configurations. This paper presents and describes a summary of mechanical properties of the plasma-sprayed coating material to provide them as a design database. 相似文献
3.
Yu Jia Yuji Hotta Kimiyasu Sato Koji Watari 《Journal of the American Ceramic Society》2006,89(3):1103-1106
ZrO2 –Al2 O3 nanocomposite particles were synthesized by coating nano-ZrO2 particles on the surface of Al2 O3 particles via the layer-by-layer (LBL) method. Polyacrylic acid (PAA) adsorption successfully modified the Al2 O3 surface charge. Multilayer coating was successfully implemented, which was characterized by ξ potential, particle size. X-ray diffraction patterns showed that the content of ZrO2 in the final powders could be well controlled by the LBL method. The powders coated with three layers of nano-ZrO2 particles, which contained about 12 wt% ZrO2 , were compacted by dry press and cold isostatically pressed methods. After sintering the compact at 1450°C for 2 h under atmosphere, a sintered body with a low pore microstructure was obtained. Scanning electron microscopy micrographs of the sintered body indicated that ZrO2 was well dispersed in the Al2 O3 matrix. 相似文献
4.
Peiling Ke Qimin Wang Weigang Hua Jun Gong Chao Sun Yanchun Zhou 《Journal of the American Ceramic Society》2007,90(3):936-941
After depositing a Ni–32Co–20Cr–8Al–0.5Y–1Si–0.03B (wt%) bond coat on a Ni-base superalloy using arc ion plating (AIP), a ceramic top coat with hollow spherical powder of ZrO2 –8 wt%Y2 O3 (HSP–YSZ) was deposited using detonation gun (D-gun) spraying. Thermal exposure behaviors of thermal barrier coatings (TBCs) were investigated at 1100°C. The thermal growth oxides (TGO) layer thickened and became more undulated during thermal exposure. Yttrium aluminum garnet (YAG) was observed within TGO, which produced thickness imperfections and thus aided to build up out-of-plane stresses. As a result, radial cracks initiated at the defects around TGO imperfections and separation developed through crack nucleation, propagation, and coalescence at the weaker TGO/bond coat interface. With further thermal exposure, coalescence of interfacial separations created a connected crack. The TBC detached and final failure occurred at the TGO/bond coat interface, leading to spallation of TBC when cooling to ambient. The stress distributions in the TGO layer with different thermal exposure times were also measured using luminescence spectroscopy. The stresses were independent of time after a transient period from θ-Al2 O3 to α-Al2 O3 scale. It is suggested that the lifetime of AIP/D-gun TBCs with an HSP–YSZ coat is controlled by the initiation and linking of a sub-critical interfacial crack. 相似文献
5.
Srinivasan Raghavan Hsin Wang Ralph B. Dinwiddie Wallace D. Porter Robert Vaen Detlev Stöver Merrilea J. Mayo 《Journal of the American Ceramic Society》2004,87(3):431-437
Zirconia doped with 3.2–4.2 mol% (6–8 wt%) yttria (3–4YSZ) is currently the material of choice for thermal barrier coating topcoats. The present study examines the ZrO2 -Y2 O3 -Ta2 O5 /Nb2 O5 systems for potential alternative chemistries that would overcome the limitations of the 3–4YSZ. A rationale for choosing specific compositions based on the effect of defect chemistry on the thermal conductivity and phase stability in zirconia-based systems is presented. The results show that it is possible to produce stable (for up to 200 h at 1000°–1500°C), single (tetragonal) or dual (tetragonal + cubic) phase chemistries that have thermal conductivity that is as low (1.8–2.8W/m K) as the 3–4YSZ, a wide range of elastic moduli (150–232 GPa), and a similar mean coefficient of thermal expansion at 1000°C. The chemistries can be plasma sprayed without change in composition or deleterious effects to phase stability. Preliminary burner rig testing results on one of the compositions are also presented. 相似文献
6.
Zirconia-rich subsolidus phase relationships in the ZrO2 –Sc2 O3 and ZrO2 –In2 O3 systems were investigated. Phase inconsistencies in the ZrO2 –Sc2 O3 system resulted from a diffusionless cubic-to-tetragonal ( t' ) phase transformation not being recognized in the past. Through three different measuring techniques, along with microstructural observations, the solubility limits of the tetragonal and cubic phases were determined. 相似文献
7.
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
8.
Ana M. Espino Luis A. Díaz Adolfo Fernández Ramón Torrecillas José S. Moya 《Journal of the American Ceramic Society》2005,88(4):1000-1003
The wettability of binary and ternary glasses belonging to SiO2 –Al2 O3 –ZrO2 diagram has been studied using the sessile drop technique at 1750° and 1800°C. The ternary SiO2 –Al2 O3 –ZrO2 (90–5–5 wt%) glass has proved to be well appropriated as a molybdenum oxidation barrier coating. The addition of 5 wt% of MoO2 slightly improves its wettablity at higher temperatures without affecting its oxidation barrier properties. The Mo comes into the glass network as a mixture of Mo5+ , Mo4+ , and Mo6+ . After oxidation at 1000°C in oxygen atmosphere, the molybdenum remains in the glass network as Mo6+ . 相似文献
9.
Novel Mg2 Zr5 O12 /Mg2 Zr5 O12 –ZrO2 –MgF2 Gradient Layer Coating on Magnesium Formed by Microarc Oxidation
A novel Mg2 Zr5 O12 -based coating on magnesium was formed by microarc oxidation (MAO) in a K2 ZrF6 -containing electrolyte. The structure of the coating was examined by X-ray diffraction using the grazing angle method, scanning electron microscopy, and transmission electron microscopy. The friction and wear properties of the MAO-coated and -uncoated Mg samples were evaluated in a ball-on-disk testing system. The corrosion resistance of the coating in a 3.5% NaCl solution was investigated by the potentiodynamic polarization test. The coating is relatively dense and composed of a Mg2 Zr5 O12 –ZrO2 –MgF2 inner layer and a nanocrystalline Mg2 Zr5 O12 outer layer with a maximum hardness of 1240 Hv. The friction coefficient of the coating against Si3 N4 is 0.35 under a dry-sliding condition. The corrosion resistance of the magnesium substrate is improved considerably by MAO treatment. The corrosion potential of the Mg2 Zr5 O12 -coated sample is −1.43 V with a current density as low as 7.06 × 10−8 A/cm2 . It is expected that the coating can considerably protect magnesium from wear and corrosion. 相似文献
10.
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
11.
S. P. KRAUS-LANTERI T. E. MITCHELL A. H. HEUER 《Journal of the American Ceramic Society》1986,69(3):256-258
High-resolution electron microscopy was used to image incoherent ZrO2 /Al2 O3 interfaces in ZrO2 -toughened Al2 O3 containing intragranular ZrO2 . These particles are generally spherical but are sometimes faceted. High-resolution electron micrographs provide atomic-level information on the interfacial structure. For spherical particles, both ledgelike images and misfit dislocation-like images accommodated the lattice misfit, depending on the orientation of the interface, while faceted particles imply at least one low-energy ZrO2 /Al2 O3 interface. 相似文献
12.
Xinbo Yang Jun Xu Hongjun Li Xiaonong Cheng Xuehua Yan 《Journal of the American Ceramic Society》2007,90(6):1953-1955
In this paper, ZrO2 and WO3 were used as the raw materials to prepare ZrO2 /ZrW2 O8 composites by in situ reaction method and the thermal expansion property of the composites was studied. This novel method included a heating step up to 1473 K for 24 h, which combines the synthesizing and sintering of ZrW2 O8 . The result indicates that ZrO2 /ZrW2 O8 composite shows near-zero thermal expansion when the weight ratio of ZrO2 and WO3 is 2.5:1. Compared with composites prepared previously by non-reactive sintering of ZrO2 and ZrW2 O8 , the composites show higher relative density and lower porosity. 相似文献
13.
Hyun M. Jang Jong H. Moon Cheol W. Jang 《Journal of the American Ceramic Society》1992,75(12):3369-3376
Al2 O3 –ZrO2 –SiC whisker composites were prepared by surface-induced coating of the precursor for the ZrO2 phase on the kinetically stable colloid particles of Al2 O3 and SiC whisker. The fabricated composites were characterized by a uniform spatial distribution of ZrO2 and SiC whisker phases throughout the Al2 O3 matrix. The fracture toughness values of the Al2 O3 –15 vol% ZrO2 –20 vol% SiC whisker composites (∼12 MPa.m1/2 ) are substantially greater than those of comparable Al2 O3 –SiC whisker composites, indicating that both the toughening resulting from the process zone mechanism and that caused by the reinforced SiC whiskers work simultaneously in hot-pressed composites. 相似文献
14.
The existence of stable and metastable forms of 2ZrO2 ·P2 O5 and the subsolidus phase relations in the system ZrO2 -ZrP2 O7 were confirmed before investigation of the ternary system. The synthesis and thermal behavior of ZrW2 O8 were reinvestigated, and the system WO3 -P2 O5 was examined cursorily. A ternary compound, 2ZrO2 ·WO3 ·P2 O5 , was found, and compatibility triangles for the system between 1105° and 1150°C were established. The ternary compound is compatible with ZrO2 , WO3 , and three binary compounds, giving rise to five composition triangles. In addition, ZrP2 O7 , WO3 , and "W2 O3 (PO4 )2 " were compatible. 相似文献
15.
Ana E. Bohé Julio Andrade-Gamboa Daniel M. Pasquevich Alfredo J. Tolley Jorge L. Pelegrina 《Journal of the American Ceramic Society》2000,83(4):755-760
The microstructure of ZrO2 fine particles produced by a novel synthesis method at 450° and 950°C has been studied. The fundamentals of the synthesis method, which involves both chemical and diffusion phenomena, are presented. The method is based on mass transport through the gaseous phase between metallic zirconium and Fe2 O3 powder. The mass-transporting chemical species are zirconium and iron chlorides. This article focuses on the microstructure and structure of ZrO2 particles formed by the reaction between gaseous ZrCl4 and solid Fe2 O3 , which is a relevant reaction step that occurs during the synthesis process. The resulting ZrO2 crystals grown on Fe2 O3 particles have been analyzed using transmission electron microscopy. Microstructural characterization has been complemented by X-ray diffractometry analysis. Tetragonal-ZrO2 is produced at 450°C and monoclinic-ZrO2 single crystals are produced at 950°C. 相似文献
16.
Dae-Joon Kim Paul F. Becher Camden R. Hubbard 《Journal of the American Ceramic Society》1993,76(11):2904-2908
Tetragonal ZrO2 ( t -ZrO2 ) solid solutions were prepared with addit ons of 2 mol% Y2 O3 plus up to 0.45 mol% Nb2 O5 . The thermal expansion coefficients in both the a- and c -axis lattice directions increased with Nb2 O5 alloying and the thermal expansion in the c -axis direction was greater than that in the a -axis direction over the entire composition range. This anisotropic thermal expansion behavior was related to the 4-fold coordination of Nb5+ with oxygen ions in t -ZrO2 solid solutions in the system ZrO2 –Y2 O3 –Nb2 O5 . The fracture toughness continuously increased with Nb2 O5 alloying and suggested that the c/a axial ratio is a more significant factor than the internal stress that arises from the thermal expansion anisotropy, in the determination of the transformability of t -ZrO2 in this system. 相似文献
17.
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
18.
Toughening of MoSi2 for high-temperature applications can be achieved by incorporating ductile refractory-metal reinforcements, provided that a coating is applied to prevent interdiffusion and reaction between the matrix and the reinforcements. In the present study, three different coating techniques for applying a thin Al2 O3 film on Nb reinforcements as a diffusion barrier have been studied. The techniques consisted of (i) sol-gel coating; (ii) physical vapor deposition (PVD); (iii) hot dipping in molten Al, followed by anodizing Al to form Al2 O3 . The processing parameters for the techniques were evaluated and the effectiveness of each coating as a diffusion barrier was assessed. For the present MoSi2 matrix which contains SiO2 , PVD coatings provided the most effective diffusion barrier for processing MoSi2 /Nb composites. 相似文献
19.
The phase relations in the systems MgO-Y2 O3 -ZrO2 and CaO-MgO-ZrO2 were established at 1220° and 1420°C. The system MgO-Y2 O3 -ZrO2 possesses a much-larger cubic ZrO2 solid solution phase field than the system CaO-MgO-ZrO2 at both temperatures. The ordered δ phase (Zr3 Y4 O12 ) was found to be stable in the system ZrO2 -Y2 O3 at 1220°C. Two ordered phases φ1 (CaZr4 O9 ) and φ2 (Ca6 Zr19 O44 ) were stable at 1220°C in the system ZrO2 -CaO. At 1420°C no ordered phase appears in either system, in agreement with the previously determined temperature limits of the stability for the δ, φ1 , and φ2 phases. The existence of the compound Mg3 Yz O6 could not be confirmed. 相似文献
20.
Properties of glasses in the system Y2 O3 –Al2 O3 –SiO2 containing Na2 O and ZrO2 were investigated. The difference between the thermal expansion coefficients (Δα) at temperatures above T g and those below T g , microhardness, density, and chemical durability were measured in relation to the Al2 O3 /Y2 O3 molar ratio. These glasses were found to have a smaller value of Δα than that of a commercial coating glass. 相似文献