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 共查询到10条相似文献,搜索用时 109 毫秒
1.
Double-ceramic-layer (DCL) thermal barrier coatings (TBCs) of La2(Zr0.7Ce0.3)2O7 (LZ7C3) and La2Ce2O7 (LC) were deposited by electron beam-physical vapor deposition (EB-PVD). The composition, interdiffusion, surface and cross-sectional morphologies, cyclic oxidation behavior of DCL coating were studied. Energy dispersive spectroscopy and X-ray diffraction analyses indicate that both LZ7C3 and LC coatings are effectively fabricated by a single LZ7C3 ingot with properly controlling the deposition energy. The chemical compatibility of LC coating and thermally grown oxide (TGO) layer is unstable. LaAlO3 is formed due to the chemical reaction between LC and Al2O3 which is the main composition of TGO layer. Additionally, the thermal cycling behavior of DCL coating is influenced by the interdiffusion of Zr and Ce between LZ7C3 and LC coatings. The failure of DCL coating is a result of the sintering of LZ7C3 coating surface, the chemical incompatibility of LC coating and TGO layer and the abnormal oxidation of bond coat. Since no single material that has been studied so far satisfies all the requirements for high temperature applications, DCL coating is an important development direction of TBCs.  相似文献   

2.
A new class of materials for ultrasonic matching layers is presented. The materials consist of nanoscale cerium oxide particles in an epoxy functionalized organic inorganic hybrid polymer matrix. The cerium oxide agglomerates to particles with 20 nm diameters. The content of particles in the polymer matrix could be increased to 75 wt.% which corresponds to 37 vol.%. The most technical important piezoelectrical ceramics have an acoustic impedance of about 30 MRayl, to improve coupling into water or biological tissue with an acoustic impedance of about 1.5 MRayl a matching layer should have an acoustic impedance of about 6.8 MRayl. With a filling degree of 75 wt.% the new composite material reaches an acoustic impedance of 7 MRayl. The materials are synthesized by a hydrolytic condensation combined with polymerization. This way of synthesis allows the use of organic solvents to adjust the viscosity of the sol and the application of different coating techniques. Ultrasound transducers (100 MHz) were built to test the new matching layers and an increase of the voltage signal amplitude of about 100% could be detected.  相似文献   

3.
Microscopic observation of laser glazed yttria-stabilized zirconia coatings   总被引:2,自引:0,他引:2  
Thermal barrier coatings (TBCs) are frequently used as insulation system for hot components in gas-turbine, combustors and power plant industries. The corrosive gases which come from combustion of low grade fuels can penetrate into the TBCs and reach the metallic components and bond coat and cause hot corrosion and erosion damage. Glazing the top coat by laser beam is advanced approach to seal TBCs surface. The laser beam has the advantage of forming a dense thin layer composed of micrograins. Plasma-sprayed yttria-stabilized zirconia (YSZ) coating was glazed with Nd-YAG laser at different operating conditions. The surface morphologies, before and after laser treatment, were investigated by scanning electron microscopy. Laser beam assisted the densification of the surface by remelting a thin layer of the exposed surface. The laser glazing converted the rough surface of TBCs into smooth micron-size grains with size of 2-9 μm and narrow grain boundaries. The glazed surfaces showed higher Vickers hardness compared to as-sprayed coatings. The results revealed that the hardness increases as the grain size decreases.  相似文献   

4.
In situ formation of ceramic coatings on Q235 carbon steel was achieved by plasma electrolytic oxidation (PEO) in carbonate electrolyte and silicate electrolyte, respectively. The surface and cross-section morphology, phase and elemental composition of PEO coatings were examined by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). The bond strength of the coating was determined using a direct pull-off test. The hardness as well as tribological properties of the ceramic coating was primarily studied. The results indicated that the coating obtained in carbonate electrolyte was Fe3O4, while the coating achieved from silicate electrolyte was proved to be amorphous. Both kinds of coatings showed coarse and porous surface. The Fe3O4 coatings obtained in carbonate electrolyte showed a high bonding strength to the substrate up to 20 ± 2 MPa and the value was 15 ± 2 MPa for the amorphous coatings obtained in carbonate electrolyte. The micro hardness of the amorphous coating and the Fe3O4 coating was 1001 Hv and 1413 Hv, respectively, which was more than two and three times as that of the Q235 alloy substrate (415 Hv). The friction coefficient exhibited by amorphous coating and Fe3O4 coating was 0.13 and 0.11, respectively, both lower than the uncoated Q235 substrate which ranged from 0.17 to 0.35.  相似文献   

5.
p-Type transparent conducting tin-gallium oxide (TGO) films were successfully fabricated on quartz substrates by DC magnetron sputtering of GaSn alloy films followed by thermal oxidation. XRD characterization indicated that the TGO films maintain rutile structure of the tin oxide (SnO2). UV-vis transmittance spectra indicated that the films have a transmittance higher than 85% in the visible region, with an optical band-gap around 3.8 eV. Hall effect measurement showed that electrical properties of the TGO films were dependent on oxidation temperature. Oxidation at too high or low temperature was unfavorable for p-type conduction. It is found that the optimum oxidation temperature for highest hole concentration (8.84 × 1018 cm−3) was in the range of 600-650 °C.  相似文献   

6.
Son KT  Lee CC 《Ultrasonics》2012,52(4):555-563
Silver epoxy was selected to bond transducer plates on glass substrates. The properties and thickness of the bonding medium affect the electrical input impedance of the transducer. Thus, the thickness of the silver epoxy bonding layer was used as a design parameter to optimize the structure for the transducer input impedance to match the 50 Ω output impedance of most radio frequency (RF) generators. Simulation and experimental results show that nearly perfect matching is achieved without using any matching circuit. At the matching condition, the transducer operates at a frequency band a little bit below the half-wavelength resonant frequency of the piezoelectric plate. In experiments, lead titanate (PT) piezoelectric plates were employed. Both full-size, 11.5 mm × 2 mm × 0.4 mm, and half-size, 5.75 mm × 2 mm × 0.4 mm, can be well matched using optimal silver epoxy thickness. The transducer assemblies demonstrate high efficiency. The conversion loss from electrical power to acoustic power in soda-lime glass is 4.3 dB. This loss is low considering the fact that the transducers operate at off-resonance by 12%. With proper choice of silver epoxy thickness, the transducer can be matched at the fundamental, the 3rd and 5th harmonic frequencies. This leads to the possible realization of triple-band transducers. Reliability was assessed with thermal cycling test according to Telcordia GR-468-Core recommendation. Of the 30 transducer assemblies tested, none broke until 2900 cycles and 27 have sustained beyond 4050 cycles.  相似文献   

7.
In this paper, the thermal stress of the double-ceramic-layer (DCL) La2Zr2O7/8YSZ thermal barrier coatings (TBCs) fabricated by atmospheric plasma spraying (APS) during thermal shock has been calculated. The residual stress of the coating after being sprayed has been regarded as the initial condition of the first thermal cycle. The characteristic of the stress development during the thermal cycle has been discussed, and the influence of the defects on the failure mode during the thermal cycle has also been discussed systematically. Finite element simulation results show that there exist higher radial thermal shock stresses on the ceramic layer surface of these two coatings. There also exist higher thermal stress gradient at the interface between the ceramic layer and the metallic layer. Higher thermal stress in 8YSZ/NiCoCrAlY coating lead to the decrease of thermal shock property as compared to that of LZ/8YSZ/NiCoCrAlY coating. The addition of LZ ceramic layer can increase the insulation temperature, impede the oxygen transferring to the bond coating and can also reduce the thermal stress. Considering from the aspects of thermal insulation ability and the thermal shock resistance ability, DCL type LZ/8YSZ TBCs is a more promising coating material compared with the single-ceramic-layer (SCL) type 8YSZ TBCs for the application.  相似文献   

8.
Aluminum trioxide ceramic coatings with high hardness were grown on surfaces of 2024 Aluminum alloys by micro-plasma oxidation in an aluminate electrolytic solution, which highly improve wear-resisting properties of 2024 Aluminum alloys. However, ceramic coating surfaces are porous and very coarse, which is disadvantageous to practical applications. In this paper, in order to increase the density of the pores and decrease the friction coefficient of the ceramic coatings, different concentrations (2-8 g/l) of graphite were added into the aluminate electrolytic solution. The thickness and hardness of the produced ceramic coatings were measured by HVS-100 micro-hardness tester and thickness tester. The friction coefficient of the coatings was studied by a frictionometer. The phase composition and surface morphology of the MPO films were evaluated through X-ray diffraction (XRD) and scanning electron microscope (SEM). The results show that the thickness of the ceramic coating is about 22 ± 1 μm, surfaces of the ceramic coatings are very uniform and that the coatings consist of mainly aluminum trioxides and a certain amount of graphite, which indicates graphite have entered the ceramic films during the micro-plasma oxidation process. Wear properties results show that the friction coefficient of the ceramic coatings decreased when graphite entered the ceramic films. When the concentration of graphite is 4 g/l, the wear properties of the coatings is the most excellent and the friction coefficient decreases to the lowest, that is 0.09.  相似文献   

9.
Electroless deposition of Cu on poly(ethylene terephthalate) (PET) fabric modified with 3-mercaptopropyltriethoxysilane was investigated. Morphology, composition, structure, thermal decomposing behavior of copper coating PET fabric after ultrasonic washing in water for 1 h were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, X-ray photoelectron spectroscopy (XPS), Raman spectrometer, X-ray diffraction (XRD), and thermogravimetric analysis (TG), respectively. Copper plating on modified fabric has good adherence stability and high electric conductivity before and after ultrasonic washing, while copper coating fabric without modification is easily destroyed during the washing process, which leads to the textile changing from conductor to dielectric. As the copper weight on the treated fabric is 28 g/m2, the shielding effectiveness (SE) is more than 54 dB at frequency ranging from 0.01 MHz to 18 GHz.  相似文献   

10.
Bone implants made of metal, often titanium or the titanium alloy Ti6Al4V, need to be surface treated to become bioactive. This enables the formation of a firm and durable connection of the prosthesis with the living bone. We present a new method to uniformly cover Ti6Al4V with a thin layer of ceramics that imitates bone material. These calcium alkali phosphates, called GB14 and Ca10, are applied to the metal by dip coating of metal plates into an aqueous slurry containing the fine ceramic powder. The dried samples are illuminated with the 790 nm radiation of a pulsed femtosecond laser. If the laser fluence is set to a value just below the ablation threshold of the ceramic (ca. 0.4 J/cm2) the 30 fs laser pulses penetrate the partly transparent ceramic layer of 20-40 μm thickness. The remaining laser fluence at the ceramic-metal interface is still high enough to generate a thin metal melt layer leading to the ceramic fixation on the metal. The laser processing step is only possible because Ti6Al4V has a lower ablation threshold (between 0.1 and 0.15 J/cm2) than the ceramic material. After laser treatment in a fluence range between 0.1 and 0.4 J/cm2, only the particles in contact with the metal withstand a post-laser treatment (ultrasonic cleaning). The non-irradiated rest of the layer is washed off. In this work, we present results of a successful ceramic fixation extending over larger areas. This is fundamental for future applications of arbitrarily shaped implants.  相似文献   

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