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1.
Double-ceramic-layer (DCL) thermal barrier coatings (TBCs) of La2(Zr0.7Ce0.3)2O7 (LZ7C3) and Eu3+-doped zirconia, which was partially stabilised by 8 wt% yttria (8YSZ:Eu), were prepared by atmospheric plasma spraying. A thermal cycling test was carried out. The 8YSZ:Eu sublayer exposed during thermal cycling could produce visible luminescence under ultraviolet (UV) illumination, providing an indication of the spallation and damage degree of the coating. The result shows that the application of a Eu3+-doped luminescence sublayer can be a very simple and useful non-destructive technique to indicate the spallation and damage degree of DCL coatings.  相似文献   

2.
Lanthanum–zirconium–cerium composite oxide (La2(Zr0.7Ce0.3)2O7, LZ7C3) coatings were prepared under different conditions by electron beam-physical vapor deposition (EB-PVD). The composition, crystal structure, surface and cross-sectional morphologies, cyclic oxidation behavior of these coatings were studied. Elemental analysis indicates that the coating composition has partially deviated from the stoichiometry of the ingot, and the existence of excess La2O3 is also observed. The optimized composition of LZ7C3 coatings could be effectively achieved by the addition of excess CeO2 into the ingot or by properly controlling the deposition energy. Meanwhile, when the deposition energy is 1.15 × 104–1.30 × 104 J/cm2, the coating has a similar X-ray diffraction (XRD) pattern to the ingot, and the thermal cycling life of the coating is also superior to other coatings. The spallation of the coatings occurs either within the ceramic layer approximately 6–10.5 μm above its thermally grown oxide (TGO) layer or at the interface between ceramic layer and bond coat.  相似文献   

3.
This paper compares the hot corrosion performance of yttria stabilized zirconia (YSZ), Gd2Zr2O7, and YSZ + Gd2Zr2O7 composite coatings in the presence of molten mixture of Na2SO4 + V2O5 at 1050 °C. These YSZ and rare earth zirconate coatings were prepared by atmospheric plasma spray (APS). Chemical interaction is found to be the major corrosive mechanism for the deterioration of these coatings. Characterizations using X-ray diffraction (XRD) and scanning electron microscope (SEM) indicate that in the case of YSZ, the reaction between NaVO3 and Y2O3 produces YVO4 and leads to the transformation of tetragonal ZrO2 to monoclinic ZrO2. For the Gd2Zr2O7 + YSZ composite coating, by the formation of GdVO4, the amount of YVO4 formed on the YSZ + Gd2Zr2O7 composite coating is significantly reduced. Molten salt also reacts with Gd2Zr2O7 to form GdVO4. Under a temperature of 1050 °C, Gd2Zr2O7 based coatings are more stable, both thermally and chemically, than YSZ, and exhibit a better hot corrosion resistance.  相似文献   

4.
A series of La2O3–ZrO2–CeO2 composite oxides were synthesized by solid-state reaction. The final product keeps fluorite structure when the molar ratio Ce/Zr  0.7/0.3, and below this ratio only mixtures of La2Zr2O7 (pyrochlore) and La2O3–CeO2 (fluorite) exist. Averagely speaking, the increase of CeO2 content gives rise to the increase of thermal expansion coefficient and the reduction of thermal conductivity, but La2(Zr0.7Ce0.3)2O7 has the lowest sintering ability and the lowest thermal conductivity which could be explained by the theory of phonon scattering. Based on the large thermal expansion coefficient of La2Ce3.25O9.5, the low thermal conductivities and low sintering abilities of La2Zr2O7 and La2(Zr0.7Ce0.3)2O7, double-ceramic-layer thermal barrier coatings were prepared. The thermal cycling tests indicate that such a design can largely improve the thermal cycling lives of the coatings. Since no single material that has been studied so far satisfies all the requirements for high temperature thermal barrier coatings, double-ceramic-layer coating may be an important development direction of thermal barrier coatings.  相似文献   

5.
《Ceramics International》2017,43(5):4102-4111
The nanostructured single-ceramic-layer (SCL) 8YSZ thermal barrier coatings (TBCs), double-ceramic-layer (DCL) Sm2Zr2O7 (SZ)/8YSZ and SZ doped with 8 wt% CeO2 nanoscale particles (8CSZ)/8YSZ TBCs were fabricated by atmospheric plasma spraying (APS) on nickel-based superalloy substrates with NiCoCrAlY as the bond coating. The thermal cycling behavior of the three as-sprayed TBCs was investigated systematically at 1000 ℃ and 1200 ℃. The results reveal that the thermal cycling lifetime of the nanostructured DCL 8CSZ/8YSZ TBCs is the longest among them, which is largely due to the fact that the intermediate layer buffer effect of the DCL structure, more porosity and improvement of thermal expansion coefficient from doping CeO2 nanoparticles can relieve thermal stress to a great extent at elevated temperature. The failure mechanism of the nanostructured TBCs has been discussed in detail.  相似文献   

6.
《Ceramics International》2017,43(10):7797-7803
Nanostructured GdPO4 coatings, designed as the outer layer of double-ceramic-layer thermal barrier coatings (DCL-TBCs), were produced by air plasma spraying (APS). The coatings have close chemical composition to that of the agglomerated particles used for thermal spray. Nanozones with porous structure are embedded in the coating microstructure, having a percentage of ~30%. Hot corrosion tests of the coatings were carried out in V2O5 and Na2SO4+V2O5 salts at 900 °C for 4 h. Results indicate that dense reaction layers, consisting of GdVO4 and Gd4(P2O7)3, form on the coating surfaces, which could suppress further penetration of the molten salts. In the V2O5 molten salt, the reaction layer is thicker and less molten salt trace could be found beneath the layer.  相似文献   

7.
Vertical cracks are beneficial in thermal barrier coatings due to enhanced thermo-mechanical compliance. Accordingly, an aqueous nitrate based precursor solution was atomized on stainless steel substrates by spray pyrolysis to deposit thick crack-designed lanthanum zirconate coatings. Coatings with designed crack patterns were deposited and characterized by electron microscopy, tribology, Vickers indentation, and thermal diffusivity. The crystallization of the coatings was investigated by in situ high temperature X-ray diffraction. The green coatings crystallized from 600 °C and the pyrochlore structure was formed after heat treatment at 1000 °C. Crystalline lanthanum zirconate multilayered coatings with small crack spacing and crack opening exhibited a higher density, a higher hardness, lower thermal diffusivities, and higher thermal conductivities compared to crystalline monolayered coatings of similar thickness with large crack spacing and crack opening. The thermal diffusivity of the coatings, ∼28 mm2/s at room temperature, was similar to the values reported for yttria-stabilized zirconia plasma sprayed coatings.  相似文献   

8.
《Ceramics International》2015,41(6):7318-7324
Gadolinium zirconate (Gd2Zr2O7, GZ) as one of the promising thermal barrier coating materials for high-temperature application in gas turbine was toughened by nanostructured 3 mol% yttria partially-stabilized zirconia (YSZ) incorporation. The fracture toughness of the composite of 90 mol% GZ-10 mol% YSZ (GZ–YSZ) was increased by about 60% relative to the monolithic GZ. Both the GZ and GZ–YSZ composite coatings were deposited by atmospheric plasma spraying on Ni-base superalloys and then thermal-shock tested under the same conditions. The thermal-shock lifetime of GZ–YSZ composite coating was improved, which is believed to be mainly attributed to the enhancement of fracture toughness by the addition of YSZ. In addition, the failure mechanisms of the thermal-shock tested GZ–YSZ composite coatings were discussed.  相似文献   

9.
The microstructure of following thermal barrier coatings (TBC) was characterised in this paper: monolayer coatings Nd2Zr2O7 and 8YSZ; a double ceramic layered (DCL) coating. Coatings were characterised by thicknesses that did not exceed 300 μm and porosities of approx. 5%. The chemical and phase composition analysis of the DCL layers revealed an external Nd2Zr2O7 ceramic layer approx. 80 μm thick, a transitional zone approx. 120 μm thick and an internal 8YSZ layer 100 μm thick. For the case of the monolayer coating, the Nd2Zr2O7 pyrochlore phase was the only one-phase component. The surface topography of both TBC systems was typical for plasma sprayed coatings, and compressive stress state had a value of approx. 5–10 MPa. Measurements of the thermal parameters, i.e., thermal diffusivity, point to considerably better insulative properties for both new types of layers when compared to the standard 8YSZ layers.  相似文献   

10.
Thermal insulation applications have long required materials with low thermal conductivity, and one example is yttria (Y2O3)-stabilized zirconia (ZrO2) (YSZ) as thermal barrier coatings used in gas turbine engines. Although porosity has been a route to the low thermal conductivity of YSZ coatings, nonporous and conformal coating of YSZ thin films with low thermal conductivity may find a great impact on various thermal insulation applications in nanostructured materials and nanoscale devices. Here, we report on measurements of the thermal conductivity of atomic layer deposition-grown, nonporous YSZ thin films of thickness down to 35 nm using time-domain thermoreflectance. We find that the measured thermal conductivities are 1.35–1.5 W m−1 K−1 and do not strongly vary with film thickness. Without any reduction in thermal conductivity associated with porosity, the conductivities we report approach the minimum, amorphous limit, 1.25 W m−1 K−1, predicted by the minimum thermal conductivity model.  相似文献   

11.
Rare-earth zirconates with a pyrochlore structure have been developed for potential application in thermal barrier coating systems to further improve the performance and durability of gas turbines. The Sm2Zr2O7 (abbreviated as SZ) powder was synthesized by solid state reaction and then deposited by air plasma spraying. The phase stability, microstructure and thermal conductivity of SZ and 8 wt% Y2O3 stabilized zirconia (8YSZ) coatings were investigated. The X-ray diffraction results indicated that the crystal structure of the as-sprayed SZ coatings was defect-fluorite, and after heat treating at 1200 °C for 50 h, it started to transform to pyrochlore, and the content of pyrochlore increased with increase in temperature of the heat treatment. The thermal conductivities of SZ coatings were significantly lower than those of 8YSZ coatings before and after heat treatments, which increased considerably after heat treatments compared to the as-sprayed states for both coatings due to sintering effects.  相似文献   

12.
《Ceramics International》2017,43(15):12126-12137
Mechanical resistance of Al2O3 + TiO2 nanocomposite ceramic coating deposited by electrostatic spray deposition method onto X10CrAlSi18 steel to thermal and slurry tests was investigated. The coating was produced from colloidal suspension of TiO2 nanoparticles dispersed in 3 wt% solution of Al2(NO3)3, as Al2O3 precursor, in ethanol. TiO2 nanoparticles of two sizes, 15 nm and 32 nm, were used in the experiments. After deposition, coatings were annealed at various temperatures, 300, 1000 and 1200 °C, and next exposed to cyclic thermal and slurry tests. Regardless of annealing temperature and the size of TiO2 nanoparticles, the outer layer of all coatings was porous. The first five thermal cycles caused a rapid increase of aluminum content of the surface layer to 30–37 wt%, but further increase in the number of thermal cycles did not affect the aluminum content. The oxidation rate of coating-substrate system was lower during the thermal tests than during annealing. The oxidation rate was also lower for smaller TiO2 particles (15 nm) forming the coating than for the larger ones (32 nm). The protective properties of Al2O3 + TiO2 coating against intense oxidation of substrate were lost at 1200 °C. Slurry tests showed that coatings annealed at 1000 °C had the best slurry resistance, but thermal tests had weakened this slurry resistance, mainly due to decreasing adhesion of the coating.  相似文献   

13.
The purpose of the current study was evaluation and comparison of hot corrosion behaviors of plasma-sprayed conventional and nanostructured yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs). Hot corrosion studies were performed on the surface of coatings in the presence of a molten mixture of V2O5+Na2SO4 at 1000 °C for 30 h. Results indicated that the hot corrosion mechanisms of conventional and nanostructured YSZ coatings were similar. The reaction between corrosive salt and Y2O3 produced YVO4, leaching Y2O3 from YSZ and causing the detrimental phase transformation of zirconia from tetragonal to monoclinic. The nanostructured coating, as compared to its conventional counterpart, in spite of a further reaction with the corrosive salt, showed a higher degradation resistance during the hot corrosion test due to increased compliance capabilities resulting from the presence of an extra source of porosity associated with the nano-zones.  相似文献   

14.
In this study, the effect of laser glazing on the hot corrosion behavior of nanostructured thermal barrier coatings (TBCs) was investigated. To this end, the hot corrosion test of plasma-sprayed and laser-glazed thermal barrier coatings conducted against 45 wt.% Na2SO4 + 55 wt.% V2O5 molten salt at 910 °C for 30 h in open air atmosphere. The results obtained from hot corrosion test showed that the reaction between Y2O3 and the corrosive salt produced YVO4, leached Y2O3 from YSZ and led to the progressive destabilization transformation of YSZ from tetragonal to the monoclinic phase. The lifetimes of the plasma-sprayed TBCs were enhanced approximately twofold by laser glazing. Reducing the reactive specific surface area of the dense glazed layer with the molten salts and improving the stress accommodation through network cracks produced by laser glazing were the main enhancement mechanisms accounting for TBC life extension.  相似文献   

15.
《Ceramics International》2016,42(10):11966-11973
A series of spinel-type CuMn2O4 ceramic pigments were prepared by a facile and low-cost sol-gel solution combustion method and used as cost-effective materials to fabricate thickness sensitive spectrally selective (TSSS) paint coatings by a convenient spray-coating technique. The chemical component, crystalline morphology, and optical property of the copper manganese oxide ceramic pigment could be accurately controlled by altering the annealing temperature. X-ray diffraction (XRD) analysis confirmed that the ceramic pigments annealed at 500 °C for 1 h coincided well with the XRD patterns of crystalline CuMn2O4 in the JCPDS database, and there were segregated phases of CuO and Mn2O3. Furthermore, the pure spinel CuMn2O4 phase could be achieved at 900 °C for 1 h. The copper manganese oxide ceramic pigments could serve as an effective pigment for fabricating the TSSS paint coating, and the TSSS paint coatings based on ceramic pigments calcined at 900 °C showed solar absorptance of 0.895–0.905 and thermal emittance of 0.186–0.310. In addition, the accelerated thermal stability test revealed that the TSSS paint coating exhibited good thermal stability when it was exposed to air at a temperature of 300 °C for 300 h. Hence, the fabricated TSSS paint coating could be used as a solar absorber coating in the low-to-mid temperature domain.  相似文献   

16.
The key requirements for a successful thermal and environmental barrier coating (T/EBC) material include stability in high temperature water vapor, low Young's modulus, close thermal expansion coefficient (TEC) with mullite, low thermal conductivity and weak mechanical anisotropy. The current prime candidates for top coat are ytterbium silicates (Yb2SiO5 and Yb2Si2O7). A major weakness of these two silicates is the severe anisotropy in mechanical properties and thermal expansion that would lead to cracking of the coating. Thus, searching for new materials with weak mechanical and thermal anisotropy is of signification. In this work, the crystal structure, mechanical and thermal properties of a promising T/EBC candidate, Yb4Al2O9, are investigated theoretically and experimentally. Good ductility, low shear deformation resistance, low Young's modulus (151 GPa) and low thermal conductivity (0.78 W m−1 K−1) is underpinned by heterogeneous bonding characteristic and distortion of the structure. Close TEC (6.27 × 10−6 K−1) with mullite and weak mechanical anisotropy highlight the suitability of Yb4Al2O9 as a prospective T/EBC.  相似文献   

17.
We report a double-ceramic-layer (DCL) thermal barrier coating (TBC) with high-entropy rare-earth zirconate (HE-REZ) as the top layer and yttria stabilized zirconia (YSZ) as the inner layer sprayed on Ni-based superalloy by atmospheric plasma spraying. La2Zr2O7 (LZ) was selected as a reference for the HE-REZ. Thermal cycling test results demonstrate that the HE-REZ/YSZ DCL coating exhibited obviously improved thermal stability when compared to the LZ/YSZ DCL coating. The reasons for the improvement of the thermal shock resistance are considered to be the anti-sinterability of the HE-REZ ceramics during the thermal cycling test attributed to the sluggish diffusion effect and as well as the better match in the coefficient of thermal expansion of HE-REZ coating with the YSZ inner layer. In addition, the HE-REZ coating maintains fluorite structure after thermal cycling test. This study makes one step forward in the development and application of high-entropy rare-earth zirconate ceramic thermal barrier coatings.  相似文献   

18.
Corrosion resistant coatings are a promising solution to protect structural metals in harsh environments. Ceramic composite coatings made from polymer-derived ceramics are highly attractive due to the ease of their processing and the ability to work in various environments. This paper is focused on the performance of a TiSi2-filled SiOC ceramic composite coating system on 316 stainless steel (SS) substrates as a corrosion resistant coating. The best-performing quadruple-dip coatings were shown to be able to reduce the weight loss due to hot sulfuric acid (95+%, 104–107 °C) corrosion by 85% over a 30-day period. Coatings from the same system were also examined under 800 °C static (100 h) and cyclic (10 cycles) oxidation. Our results indicate that the coatings perform well under both conditions of prolonged high temperature oxidation and thermal cycling, suggesting the strong potential of this system as an environmental barrier coating (EBC).  相似文献   

19.
The single-ceramic-layer (SCL) 8YSZ (conventional and nanostructured 8YSZ) and double-ceramic-layer (DCL) La2Zr2O7 (LZ)/8YSZ thermal barrier coatings (TBCs) were fabricated by plasma spraying on nickel-based superalloy substrates with NiCrAlY as the bond coat. The thermal shock behavior of the three as-sprayed TBCs at 1000 °C and 1200 °C was investigated. The results indicate that the thermal cycling lifetime of LZ/8YSZ TBCs is longer than that of SCL 8YSZ TBCs due to the fact that the DCL LZ/8YSZ TBCs further enhance the thermal insulation effect, improve the sintering resistance ability and relieve the thermal mismatch between the ceramic layer and the metallic layer at high temperature. The nanostructured 8YSZ has higher thermal shock resistance ability than that of the conventional 8YSZ TBC which is attributed to the lower tensile stress in plane and higher fracture toughness of the nanostructured 8YSZ layer. The pre-existed cracks in the surface propagate toward the interface vertically under the thermal activation. The nucleation and growth of the horizontal crack along the interface eventually lead to the failure of the coating. The crack propagation modes have been established, and the failure patterns of the three as-sprayed coatings during thermal shock have been discussed in detail.  相似文献   

20.
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   

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