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1.
Preparation of 3YSZ/Al2O3-platelet composites always requires high temperature, long duration, and/or high pressure. Herein, 3YSZ/Al2O3-platelet composites are prepared at low temperature of 492°C-645°C in 30 seconds by flash sintering under the electric field of 300-800 V/cm. The influence of electric field and current limit on the densification and grain growth of composites is investigated. The onset temperature for flash sintering is determined by electric field, which is decreased with increasing the electric field. Under the constant electric field, the current limit has a great effect on the density and grain size of composite. The flash-sintered 3YSZ/Al2O3-platelet composites exhibit relatively high hardness and elastic modulus. Both Joule heating and defects generation are proposed to be responsible for the rapid densification in flash sintering. This work demonstrates the feasibility of employing the flash sintering to prepare ceramic composites with fine grain size.  相似文献   

2.
3YSZ green layers approximately 10 μm thick were screen-printed onto 3YSZ substrates and their constrained sintering kinetics were measured at 1100-1350 °C using an optical dilatometer. The densification rates of the same powder in the form of pellets and free-standing films were also measured. The constrained densification rate was greatly retarded compared with the free densification rate at a given temperature and density. The retardation increased with increasing density and temperature and could not be properly accounted for by existing theories of constrained sintering. As a result the apparent activation energy is much lower for constrained sintering (135 ± 20 kJ mol−1) than for free sintering (660 ± 30 kJ mol−1). It is proposed that this is because the constrained microstructure exhibits larger and more widely separated pores at the higher temperatures.  相似文献   

3.
本文分别采用三种叠层方式制备YSZ/Al2O3/YSZ多层陶瓷,通过实验得出:由于YSZ与Al2O3陶瓷烧结性能的差异,导致YSZ与Al2O3陶瓷叠层共烧时容易分层翘曲,YSZ与Al2O3主要依靠层间的物理啮合作用而结合。通过在流延YSZ层与丝网印刷Al2O3层之间增加印刷YSZ过渡层的叠层方法,可以改善YSZ流延层与Al2O3丝网印刷层之间的结合,而得到结合良好的YSZ/Al2O3/YSZ多层陶瓷共烧结合界面。  相似文献   

4.
《Ceramics International》2023,49(19):31794-31801
In this paper, BNNSs/Al2O3 composite powder was prepared by in-situ reaction using borate nitridation method and BNNSs/Al2O3 composite ceramics were prepared by hot-pressing sintering. This method achieves uniform mixing of BNNSs and Al2O3 ceramic matrix and reduces the introduction of impurities in the processing process. The BNNSs/Al2O3 composite ceramics have excellent bending strength (549.4 MPa), fracture toughness (5.18 MPa m1/2) and hardness (21.3 GPa). The high hardness of composite ceramics is attributed to high grain boundary strength and density. The reinforcing mechanisms of ceramics include BNNSs pull-out, BNNSs bridging, crack deflection as well as the transgranular fracture and intergranular fracture of Al2O3 matrix.  相似文献   

5.
The thermal conductivities/diffusivities of YSZ/Al2O3 composites have been investigated by a laser flash technique. The thermal conductivity of the composite increases with an increase in the Al2O3 volume fraction, and it can be fitted well to the Maxwell theoretical model. The consistency of the thermal conductivities of the composites with the predicted values indicates the absence of obvious interfacial thermal resistances in the composites. The negligible thermal resistance effect from the YSZ and Al2O3 grain boundaries is due to the much lower phonon mean free path compared with the grain size in the composite. The low Kapitza resistance of the YSZ/Al2O3 interface is discussed in terms of the “clean” and coherent nature of the YSZ/Al2O3 interface, together with the small difference between the elastic properties of YSZ and Al2O3.  相似文献   

6.
Thermal barrier coatings (TBCs) comprising of yttria stabilized zirconia (YSZ) ceramic top coat and CoNiCrAlY metallic bond coat have been widely used in gas turbines. However, the developed oxides layer in the interface of the top and bond coats during thermal exposure of the TBCs always results in the destruction of the system. In order to restrain the growth of oxides layer and improve the thermal shock resistance of TBCs, a thin Al2O3 film was pre-deposited on CoNiCrAlY bond coat by physical vapor deposition (PVD) technology. After thermal exposure, morphologies and phase compositions of the thermal growth oxides (TGO) layer in the conventional and pre-deposited Al2O3 film TBCs were examined by scanning electron microscopy (SEM) equipped with energy dispersive spectrometer (EDS). The residual stresses in the coatings were analyzed using micro-Raman spectroscopy (LabRam-1B). It was found that TGO layer formed in the conventional TBCs was mainly composed of Al2O3, (Cr,Al)2O3 + (Co,Ni)(Cr,Al)2O4 + NiO (CSN), and (Cr,Al)2O3 + (Co,Ni)(Cr,Al)2O4 (CS), while in the treated TBCs, the formed TGO layer appeared more uniform and compact. The CSN and CS clusters, which are normally considered as a weakness for TBCs, were greatly limited. The residual stresses in the TBCs after thermal shock were also reduced by the deposition of Al2O3 film.  相似文献   

7.
《Ceramics International》2019,45(15):18899-18907
ZrO2/yttria-stabilized zirconia (YSZ) doping Al2O3 ceramic coating was fabricated via cathodic plasma electrolytic deposition (CPED) technique. The microstructures and the chemical and phase compositions of the doped coating were characterized, the mechanical properties and the high temperature oxidation resistance were evaluated, and the doping mechanism was also discussed in detail. The results showed that, doped Zr4+ and Y3+ ions could effectively reduce the working voltage during CPED process and increase the content of metastable γ-Al2O3 in the coating. Accordingly, the doped ZrO2/YSZ significantly refined the grain size of Al2O3, as well as remarkably improved the high temperature oxidation resistance, the micro-structural compactness and hardness of the Al2O3 CPED coating. This study displayed here constructed an efficiently method for the fabrication of multifunctional coating on the surface of TiAl alloy.  相似文献   

8.
This work presents the initial results of the dry-sliding wear behavior of 3 mol% yttria-stabilized zirconia reinforced with 5 vol% alumina-niobium carbide (3Y-TZP/5 vol% Al2O3-NbC) nanocomposites sintered by conventional sintering and spark plasma sintering methods in the temperature range of 1350-1450°C. The reinforcement of 3Y-TZP matrix with hard nanoparticles aimed to improve wear strength of the composites. Wear tests were performed by the ball-on-disc method using alumina (Al2O3) and tungsten carbide with 6 wt% cobalt cermet (WC-6%Co) balls as counter-materials, a load of 15 N, a sliding distance of 2000 m, and a sliding speed of 0.1 m/s. Wear behavior was evaluated in terms of wear rate and FE-SEM micrograph analysis of the wear tracks. The nanocomposite sintered at 1450°C by conventional sintering exhibited the least wear when tested with the WC-6%Co ball. Generally, the wear mechanism showed evidence of severe wear regime with both counter-materials.  相似文献   

9.
Al2O3/Al2O3 ceramic matrix composites (CMC) are candidate materials for hot-gas leading components of gas turbines. Since Al2O3/Al2O3 CMC are prone to hot-corrosion in combustion environments, the development of environmental barrier coatings (EBC) is mandatory. Owing to its favorable chemical stability and thermal properties, Y2O3 is considered a candidate EBC material for Al2O3/Al2O3 CMC. Up to 1 mm thick Y2O3 coatings were deposited by means of air plasma spraying (APS) on Al2O3/Al2O3 CMC with a reaction-bonded Al2O3 bond-coat (RBAO). APS Y2O3 coatings exhibit a good adherence in the as-deposited state as well as upon isothermal annealing up to 1400 °C. Moreover, furnace cyclic testing performed at 1200 °C revealed an excellent durability. This is explained by the formation of a continuous, approximately 1 μm thick reaction zone at the APS Y2O3/RBAO interface. The reaction zone between Y2O3 and Al2O3 comprises three layers of thermodynamically stable yttrium-aluminates exhibiting strong bonding, respectively.  相似文献   

10.
《Ceramics International》2023,49(6):9173-9184
The effects of Al2O3 content on the sintering behaviour, microstructure, and physical properties of Al2O3/vitrified bonds (SiO2–Al2O3–B2O3–BaO–Na2O–Li2O–ZnO–MgO) and Al2O3/vitrified bond cubic boron nitride (CBN) composites were systematically investigated using X-ray diffraction, differential scanning calorimetry, dilatometry, scanning electron microscopy, and X-ray photoelectron spectroscopy. Various amounts of Al2O3 promoted the formation of BaAl2Si2O8 and γ-LiAlSi2O6, increasing the relative crystallinity of the Al2O3/vitrified composite from 85.0 to 93.2%, resulting in residual compressive stress on BaAl2Si2O8, thereby influencing the thermal behaviour and mechanical properties of the Al2O3/vitrified composite. The bulk density, porosity, flexural strength, hardness, and thermal conductivity of 57.5 wt% Al2O3 sintered at 950 °C were 3.12 g/cm3, 6.1%, 169 MPa, 90.5 HRC, and 4.17 W/(m·K), respectively. The coefficient of thermal expansion of the bonding material was 3.83 × 10?6 °C?1, which was comparable to that of CBN, and the number of N–Al bonds were increased, which boosted the flexural strength of the Al2O3/vitrified CBN composite to 81 MPa. The excellent mechanical properties, compact structure, and suitable interfacial bonding state with the CBN grains of the Al2O3/vitrified composite make it a promising high-performance bonding material for superhard abrasive tools.  相似文献   

11.
《Ceramics International》2016,42(7):8005-8009
Slip-cast ceramic samples of the system (100−x) (ZrO2–3.5 mol% Y2O3)–xAl2O3 (abridged as (100−x) 3.5 YSZ/xAl2O3 composite, where x is expressed in wt%) were examined using dilatometry, isothermal sintering and electron microscopy methods. The shrinkage in the range 1100–1300 °C was found to be higher for the (100−x) 3.5 YSZ/xAl2O3 samples with prevailing fraction of PSZ than for the composites with a corundum matrix. When the weight fraction of corundum was increased, the relative shrinkage of the (100−x) 3.5 YSZ/xAl2O3 samples decreased and the open porosity of the ceramic materials grew. The effect of <gamma>-Al2O3 impurity on the sintering process and linear dimensions of ceramics is shown. Heat treatment of (50–40) 3.5 YSZ/(50–60) Al2O3 composites at 1300 °C are proposed as the optimum conditions for porous diaphragm formation.  相似文献   

12.
《应用陶瓷进展》2013,112(3):99-102
Abstract

The applicability of electrophoretic deposition (EPD) for the fabrication of single layer and multilayer ceramic coatings on dense ceramic composite materials has been examined. Al2O3/Y-tetragonal zirconia polycrystal (TZP) functionally graded composites of tubular shape were successfully coated with a two layer coating comprising porous alumina and dense reaction bonded mullite layers. The dual layer coating structure was designed to eliminate the numerous cracks caused by volume shrinkage during sintering of the individual EPD formed layers. In another example, mullite fibre reinforced mullite matrix composites were coated with a thin layer of nanosized silica particles using EPD. The aim was to achieve a compressive residual stress field in the silica layer on cooling from sintering temperature, in order to increase composite fracture strength and toughness. The EPD technique proved to be a reliable method for rapid preparation of single layer and multilayer ceramic coatings with reproducible thickness and microstructure on ceramic composite substrates.  相似文献   

13.
This paper describes a preliminary investigation of a nanocomposite ceramic coating system, based on Al2O3/SiC. Feedstock Al2O3/SiC nanocomposite powder has been manufactured using sol-gel and conventional freeze-drying processing techniques and then low pressure plasma sprayed onto stainless steel substrates using a CoNiCrAlY bond coat. Coatings of a commercial Al2O3 powder have also been manufactured as a reference for phase transformations and microstructure. The different powder morphology and size distribution resulting from the different processing techniques and their effect on coating microstructure has been investigated. Phase analysis of the feedstock powders and of the as-sprayed coatings by X-ray diffractometry (XRD) and nuclear magnetic resonance (NMR) showed that the nano-scale SiC particles were retained in the composite coatings and that equilibrium α-Al2O3 transformed to metastable γ- and δ-Al2O3 phases during plasma spraying. Other minority phases in the sol-gel Al2O3/SiC nanocomposite powder such as silica and aluminosilicate were removed by the plasma-spraying process. Microstructure characterisation by scanning electron microscopy (SEM) of the as-sprayed surface, polished cross-section, and fracture surface of the coatings showed evidence of partially molten and unmolten particles incorporated into the predominantly lamella microstructure of the coating. The extent of feedstock particle melting and consequently the character of the coating microstructure were different in each coating because of the effects of particle morphology and particle size distribution on particle melting in the plasma.  相似文献   

14.
BaTiO3/CoFe2O4 bilayer films on high temperature resistant Al2O3/Pt substrates were fabricated using the electrophoretic deposition (EPD) method. Powder synthesis, suspension preparation and kinetics of deposition were investigated in detail. Two different sintering temperatures were tested and the resultant microstructure and properties of ceramic films were investigated. The composite films sintered at a temperature of 1200 °C/2 h yielded optimal microstructures and properties. The obtained bilayer films had a dense structure with no phase diffusion or passive layer. Besides to ferroelectric and magnetic properties, magnetoelectric (ME) coupling properties were also confirmed by the magnetic anisotropy and magnetic field induced polarization investigation. The composite films showed a increased Ps from 16.2 to 16.85 μC/cm2 with variations ΔPs of 4% when the magnetic field was applied in parallel direction and a decreased Ps from 16.2 to 14.9 μC/cm2 with variations ΔPs of ?8% when a normal direction field was applied.  相似文献   

15.
Al2O3/SiC nanocomposites are usually prepared by hot pressing or using high sintering temperatures, viz. 1700°C. This is due to the strong inhibiting effect of the nano-sized SiC particles on the densification of the material. Liquid phase sintering (LPS) can be used to improve densification. This work explored two eutectic additive systems, namely MnO2.SiO2 (MS) and CaO.ZnO.SiO2 (CZS). The additive content in Al2O3/5 wt% SiC nanocomposite material varied from 2 to 10 wt%. Densities of up to 99% of the theoretical value were achieved at temperatures as low as 1300°C. Characterisation of the materials by XRD, indicated the formation of secondary crystalline phases in addition to Al2O3 and SiC. SEM and TEM analysis showed the presence of a residual glassy phase in the grain boundaries, and an increase in the average grain size when compared to nanocomposites processed without LPS additives.  相似文献   

16.
Dense alumina ceramics doped with 5 wt% 4CuO-TiO2-2Nb2O5 composite sintering aids were obtained at low sintering temperatures of 950∼975 °C. The ceramic sintered at optimal condition shows good microwave dielectric properties (εr = 12.7, Q × f = 7400 GHz), high thermal conductivity (18.4 W/m K) and high bending strength (320 MPa). TEM and EDS analysis revealed that amorphous Cu-Ti-Nb-O interfacial films with nanometer thickness formed at the grain boundaries, which could provide paths of mass transportation for densification. Al3+ ions may be involved in mass transportation through substitution by Ti3+ and Ti4+ ions near the grain boundary during the sintering process. The accumulation of copper ions at the trigeminal grain boundary was observed. The migration and reaction of copper ions in grain boundaries may also play an important role in promoting mass transportation and low-temperature densification of alumina ceramics.  相似文献   

17.
《Ceramics International》2020,46(14):22276-22281
We present the results of electron-beam sintering of composite ceramic compacts based on alumina and titanium powders. The electron beam was generated by a plasma-cathode electron source at elevated pressure values of the fore-vacuum range. We have studied the effect of the pressed compact thickness on the sintered sample parameters. It has been established that the pressed thickness significantly affects the uniformity of parameters. The samples with the most uniform parameters were obtained for thickness values below 4 mm. At a greater thickness, the parameter non-uniformity increases considerably due to outgassing from the surface of the sintered compacts.  相似文献   

18.
Reduced Pt/Al2O3 catalysts with different chloride contents were treated at different temperatures under oxygen flow. TPR and TPD studies of oxidized species show that at low Cl/Pt atomic ratio (1) PtO2 is formed at low temperature (400–500 K) and is totally decomposed (900 K) yielding reduced metallic Pt and inducing metal sintering. At high Cl/Pt atomic ratio (6) formation of stable (up to 1000 K) platinum oxichloride avoids metal sintering.  相似文献   

19.
初步研究了电沉积Ni-W-Al2O3纳米复合镀层的制备工艺。考察了纳米粒子的分散方式、纳米粒子在镀液中的浓度以及镀液温度对沉积速度、复合量及镀层形貌的影响。结果表明:纳米粒子加入镀液前超声分散1h、施镀时对镀液采用超声搅拌效果最佳;纳米粒子在镀液中的含量为15g/L时沉积速率最大,为2.88g/(dm2·h);镀液温度为75~80°C时沉积速率较大且较稳定,且当施镀温度为75°C时镀层表面均匀有光泽,呈银白色。  相似文献   

20.
YSZ/Al2O3 micro-laminated coatings were successfully prepared on the surface of MCrAlY substrates by means of electrolytic deposition and microwave sintering. The as-prepared YSZ/Al2O3 coatings were characterized by high-resolution field emission SEM and XRD. Laminated structures of alternate YSZ and Al2O3 layers were observed in the coating with the phase composition of Y2O3 stabilized t-ZrO2, α-Al2O3 and θ-Al2O3. High-temperature cyclic oxidation test at 1000 °C in air was also performed to investigate the oxidation and spallation resistance of such coatings on MCrAlY substrates. The results indicate that such coatings exhibit not only excellent oxidation resistance but also good spallation resistance under thermal cycling due to the structure of multi-sealed Al2O3 layers and the preferable high-temperature mechanical properties induced by the designed laminated composite structures, respectively.  相似文献   

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