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1.
《Ceramics International》2016,42(12):13491-13496
Two kinds of novel Ln2LaTaO7 (Ln=Er and Yb) ceramics were prepared via high-temperature solid reaction method. The phase composition, micro-morphology and thermophysical properties were investigated. Results indicate that pure Ln2LaTaO7 ceramics with single fluorite-type structure are synthesized successfully. The thermal conductivities of Er2LaTaO7 and Yb2LaTaO7 are in the range of 1.22–1.43 W/m K and 1.17–1.51 W/m K, respectively, which are much lower than that of YSZ. The lower thermal conductivity can be attributed to the phonon scattering caused by oxygen vacancies and the substituting atoms. The average thermal expansion coefficients of Yb2LaTaO7 and Er2LaTaO7 are 9.94×10−6/K and 9.63×10−6/K, respectively. As compared with Yb2LaTaO7, the higher thermal expansion coefficient of Er2LaTaO7 can be ascribed to its lower ionic-bond strength between cations at sites A and B. 相似文献
2.
W. Fan Z.Z. Wang Y. Bai J.W. Che R.J. Wang F. Ma W.Z. Tao G.Y. Liang 《Journal of the European Ceramic Society》2018,38(13):4502-4511
Due to the limited temperature capability of current YSZ thermal barrier coating (TBC) material, considerable effort has been expended world-wide to research new candidates for TBC applications above 1200?°C. Our study suggested that Sc2O3 and Y2O3 co-doped ZrO2 (ScYSZ) had excellent t’ phase stability even after annealed at 1500?°C for 336?h. The thermal expansion coefficient of ScYSZ was comparable to the value of YSZ. The thermal conductivity of fully dense ScYSZ was in the range of 2.13–1.91?W?m?1?K?1 (25–1300?°C), approximately 25% lower than that of YSZ. Although the fracture toughness of dense ScYSZ was slightly lower than YSZ, an evident decline in elastic modulus was found. Additionally, thermal cycling lifetime of plasma sprayed ScYSZ coating (914 cycles) at 1300?°C was about 2.6 times longer than its YSZ counterpart. The superior comprehensive properties confirm that ScYSZ is a prospective candidate material for high-temperature TBC application. 相似文献
3.
《Ceramics International》2016,42(12):13876-13881
High temperature gas turbine sealing can increase the thermal efficiency of a gas turbine. In this paper, monoclinic phase YTaO4 ceramics were fabricated via solid-state reaction. Phase composition and microstructures of the high-temperature-sintered YTaO4 ceramics were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and Raman Spectroscopy. Specific heat capacity rose gradually as temperature increased, due to volumetric expansion and phonon excitations. The thermal diffusivities and conductivities decreased significantly due to the effects of the porosity and phonon scattering. However, the thermal conductivities of the specimens were lower than that of 7–8 wt% yttria-stabilized zirconia (7-8YSZ), and YTaO4 ceramics have better thermal stability than current (TBCs) material. The Vickers hardnesses of YTaO4 ceramics as a function of sintering temperature were lower than that of 8YSZ, indicating YTaO4 has better fracture toughness and thermal tolerance. The results demonstrate that YTaO4 ceramics would be an excellent candidate for use as a thermal barrier coating material for high temperature gas turbines. 相似文献
4.
《Journal of the European Ceramic Society》2019,39(7):2397-2408
Forsterite-type Mg2SiO4 was investigated systematically for thermal barrier coating (TBC) applications. Results showed that Mg2SiO4 synthesized by solid-state reaction possessed the good phase stability up to 1573 K. The thermal conductivity of Mg2SiO4 at 1273 K was lower ˜20% than that of yttria stabilized zirconia (8YSZ). Mg2SiO4 also presented moderate thermal expansion coefficients, which increased from 8.6 × 10−6 K−1 to 11.3 × 10−6 K−1 (473˜1623 K). Mechanical properties including hardness, fracture toughness, and Young’s modulus of Mg2SiO4 were comparable to those of 8YSZ. The sintering results indicated a promising low-sintering activity of Mg2SiO4. Mg2SiO4 samples were subjected to water quenching test at 1573 K and showed a superior thermal shock resistance compared to 8YSZ. Mg2SiO4 coating with stoichiometric composition was produced by atmospheric plasma spraying. The thermal cycling test result showed that Mg2SiO4 coating had a lifetime more than 830 cycles at 1273 K, which is desirable for TBC applications. 相似文献
5.
《Journal of the European Ceramic Society》2023,43(5):2164-2174
Thermal barrier coatings (TBCs) are widely used as insulating layers to protect the underlying metallic structure of gas turbine blades. However, the thermal cycling performance of TBCs is affected by their complex working environments, which may shorten their service life. Previous studies have shown that preparing a mesh structure in the bonding layer can relieve thermal stress and improve the bonding strength, thereby prolonging the service life of TBCs. In this paper, a micromesh structure was prepared on the surface of the bonding layer via wet etching. The microstructure and failure mechanism of the micromesh TBCs after CMAS (CaO-MgO-Al2O3-SiO2) thermal erosion were investigated. Numerical simulation was combined with thermal shock experiments to study the stress distribution of the micromesh-structured TBCs. The results showed that the circular convex structure can effectively improve the CMAS corrosion resistance and thermal shock resistance of TBCs. 相似文献
6.
《Journal of the European Ceramic Society》2023,43(8):3658-3675
The effect of heat treatment, growth of the TGO layer, oxidation of bond coat, and the impact of the presence of two bond coats on the TBC's thermal shock resistance has been investigated experimentally. TGO oxide layers were created with two-time heat treatment of 12 and 24 h at 1000. Then the thermal shock test was performed on the APS/APS and HVOF/APS/APS samples. The results show that the use of two BCs and the presence of a thin TGO layer has a good effect on TBC performance. The presence of two BC layers increased the shock resistance by an average of 37.2%. 12 h heat treatment caused a 14.0% and 17.4% shock resistance increase in samples with the HVOF/APS/APS layer and APS/APS layer, respectively. 24 h heat treatment decreased the samples' performance by 6.7% and 10.2% for samples with two BC and one BC, respectively. 相似文献
7.
《Ceramics International》2020,46(4):4824-4831
The thermal barrier coating obtained by atmospheric plasma spraying (APS TBCs) has a distinct lamellar microstructure, in which the splats discontinuous interfaces running parallel to the metal/ceramic interface contribute largely to the reduction in the effective thermal conductivity of APS TBCs. The dependency of such contribution on the topological structure of the interface discontinuity is investigated in the present work. Firstly, the concept of discontinuity of splats interfaces was defined to quantify the splats discontinuous interfaces revealed by microscopic observations. Then, the microstructure model with a random distribution of discontinuous interfaces was established by utilizing the finite element simulation method to investigate the effect of interlayer discontinuity on thermal conductivity of the APS TBCs. Finally, an optimal topological structure of the interface discontinuity was found to be responsible for the lowest effective thermal conductivity of the APS TBCs and typical parametrical tendencies demonstrated. 相似文献
8.
《Ceramics International》2022,48(5):6681-6690
Understanding the microstructural transformation of plasma sprayed (APS) yttria-stabilized zirconia (YSZ) after experiencing the thermal shocking cycles is practically important for the coating optimization in terms of structure and performance. In this study, thermal shocking tests were conducted on the YSZ coated piston crown. The microscopic morphology and structure alteration across the YSZ coating interface over the piston crown was characterized by the ex-situ techniques. The results revealed that the YSZ coating primarily consisted of a stable tetragonal phase, without the monoclinic phase even after 800 cycles of thermal shocking. As the thermal shocking test continued, the pore number within the YSZ coating gradually decreased due to their spontaneous closure and the grain size correspondingly increased. Some visible cracks parallel to the interface consisting of YSZ and bonding layer happened at the localized regions of the YSZ coating. The stress state of YSZ coating was from originally tensile to compressive after thermal exposure, which helped prolonging the service lifetime of YSZ coating. In particular, the thermal shock resistance of plasma sprayed YSZ coated piston crown in association with the varying microstructure was also discussed. 相似文献
9.
《Ceramics International》2019,45(13):16450-16457
The study underlines the impact of Ti4+ substitution in Gd2Zr2O7 for applications in thermal barrier coatings (TBC). Depending on the Ti4+ content, two different crystal structures of Gd2Zr2O7 namely pyrochlore and fluorite were determined. Ti4+ substitutions in the increasing order induced a gradual contraction of Gd2Zr2O7 unit cell; however, with the accomplishment of concentration dependent crystal structures of either single phase pyrochlore or mixtures of pyrochlore and fluorite. Absorption measurements enunciated the enhanced infra-red reflectance behaviour of Gd2Zr2O7 due to Ti4+ substitutions. A gradual increment in the concentration of Ti4+ substitutions in Gd2Zr2O7 envisaged a simultaneous porous to dense morphological features, which reflected in the resultant mechanical data. Hot corrosion studies ensure the critical role of Ti4+ to retain the crystal structure of Gd2Zr2O7. 相似文献
10.
《Ceramics International》2020,46(4):4444-4453
In order to study the variation of rare earth oxides during thermal failure of thermal barrier coatings, Eu2O3-doped YSZ coatings with 0.5 mol%, 1.0 mol% and 1.5 mol% were prepared by explosive spraying. SEM, XRD, EDS and microhardness tester were used to analyze the effect of different rare earth oxide doping content on the morphology, composition and mechanical properties of the coatings. The results showed that with the increase of rare earth oxide doping content, the porosity of the coatings decreased, and the microhardness and fracture toughness increased. When the doping amount of rare earth oxide is 1.0 mol%, the bonding strength and thermal cycle times of the coating are the highest, 33.4 Mpa and 185 times respectively. With the increase of the doping amount of rare earth, the luminous intensity of the sprayed coating increases. After thermal shock test, the luminous intensity of Eu2O3-doped YSZ coatings at 592 and 608 nm decreased to a certain extent. 相似文献
11.
《Ceramics International》2023,49(2):2061-2072
This paper investigates the resistance of two types of thermal barrier coatings and compares their behavior with common coatings. Coatings’ layers in the first and second target sample were fabricated as HVOF/APS/APS (two bondcoats and one topcoat) and APS/APS (one bondcoat and topcoat) with diffusion pre-coating, respectively. Also, to accurately compare the behavior of these two types of coatings with conventional coatings used in gas turbines, this paper explored the resistance of three types of coatings applied as APS/APS, HVOF/APS, and HVOF coatings against thermal shock. In order to create shock loading, five types of laboratory samples were heated under regular cycles and cooled down with water. During the experiment, the sample changes caused by thermal shock loading were investigated through visual inspections. Then, after the experiment, the SEM images were leveraged to inspect the changes. In addition, changes in the structure of coating layers and their degradation process were studied. The results show that using two bond layers increases the resistance and life of the coating against heat shock by up to 1.40 times. Among the samples with one band coat, the sample with a diffusion coating applied under the BC showed the best performance. The sample life increased by 1.25 times compared to the common APS/PAS coating. 相似文献
12.
《Ceramics International》2021,47(20):28892-28903
LaMgAl11O19-type magnetoplumbite holds great promise to be used above 1300 °C as thermal barrier coatings (TBCs), but its practical application has been restricted because of inferior thermophysical properties. Herein, we focus on optimizing the thermophysical properties of LaMgAl11O19 by simultaneously substituting La3+ and Al3+ ions with Nd3+ and Sc3+ ions, respectively. Results show that the effects of co-substitution on reducing thermal conductivity are pronounced. The thermal conductivities of La1-xNdxMgAl11-xScxO19 (x = 0, 0.1, 0.2, 0.3) ceramics decrease progressively with dopant concentration and a lowest thermal conductivity of 2.04 W/(m·K) is achieved with x = 0.3 at 1000 °C, which is a value superior to pure LMA and even lower than YSZ. The mechanisms behind the lowered thermal conductivity are investigated. Increase of the thermal expansion coefficient is also realized (8.53 × 10−6 K−1 for pure LMA, 9.07 × 10−6 K−1 for x = 0.3, 1300 °C). Most importantly, Nd3+ and Sc3+ combination doping indeed facilitates mechanical properties of La1-xNdxMgAl11-xScxO19 solid solutions as well. It should be noted that Sc3+ doping at Al3+ site plays more effective role in improving thermal properties than Nd3+ does at La3+ site. This work provides a path to simultaneously integrate low thermal conductivity, good phase stability, moderate thermal expansion behavior and excellent mechanical properties on LMA for the next generation TBCs. 相似文献
13.
《Journal of the European Ceramic Society》2020,40(15):5731-5739
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
14.
Bowen Lv Robert Mücke Xueling Fan T.J. Wang Olivier Guillon Robert Vaßen 《Journal of the European Ceramic Society》2018,38(15):5092-5100
Sintering is one of the key issues in the high temperature service of thermal barrier coatings (TBCs), considering the continuously increasing operation temperature of gas-turbine for higher energy efficiency. Based on the conventional processing method of air plasma spraying (APS), suspension plasma spraying (SPS) technique has been developed recently, in order to improve the strain tolerance of TBCs. This strain tolerance of plasma-sprayed TBCs is largely effected by the sintering behavior, which is presently not fully understood. In this work, evolution of mechanical properties, in terms of Young’s modulus and viscosity, is systematically investigated by in-situ three-point bending test at 1200?°C on free-standing coatings, including micro-cracked APS, segmented APS, vertically cracked SPS and columnar structured SPS TBCs and correlated to the microstructural evolution. Based on experimental results, power law relations are proposed for the sintering induced mechanical evolution, which deepen the understanding of the sintering behavior of plasma-sprayed TBCs. 相似文献
15.
16.
《Ceramics International》2020,46(14):21939-21957
Thermal conductivity of various porous thermal barrier coatings (TBCs) used at elevated temperatures for gas turbines has been evaluated using the proposed six-phase model. These TBCs rely on microstructural properties and yield different types of porosities. This paper studies the thermal conductivity of TBCs based on microstructural features to evaluate the effect of different types of porosities on thermal conductivity. The first part of this paper investigates the microstructural characterization of various TBCs using image analysis (IA) technique. The second part of this paper evaluates the thermal conductivity using the image analysis. The volumetric fraction of porosities along with their orientation, shape and morphology, shows a considerable impact on the overall thermal conductivity of TBCs. The proposed six-phase model can predict thermal conductivity of porous TBCs with a good agreement with the measured values. The model results can help to better understand the effect of microstructural changes on thermal conductivity and can provide useful guide to fabricate TBCs with low thermal conductivity. 相似文献
17.
《Journal of the European Ceramic Society》2022,42(2):649-657
The corrosion resistance to calcium-magnesium-alumino-silicates (CMAS) is critically important for the thermal barrier coatings (TBCs). High-entropy zirconate (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 (HEZ) ceramics with low thermal conductivity, high coefficient of thermal expansion and good durability to thermal shock is expected to be a good candidate for the next-generation TBCs. In this work, the CMAS corrosion of HEZ at 1300°C was firstly investigated and compared with the well-studied La2Zr2O7 (LZ). It is found that the HEZ ceramics showed a graceful behavior to CMAS corrosion, obviously much better than the LZ ceramics. The HEZ suffered from CMAS corrosion only through dissolution and re-precipitation, while additional grain boundary corrosion existed in the LZ system. The precipitated high-entropy apatite showed fine-grained structure, resulting in a reaction layer without cracks. This study reveals that HEZ is a promising candidate for TBCs with extreme resistance to CMAS corrosion. 相似文献
18.
Xin Zhou Wenjia Song Jieyan Yuan Qingmei Gong Hao Zhang Xueqiang Cao Donald B. Dingwell 《Journal of the American Ceramic Society》2020,103(10):5599-5611
About 6-8 wt% yttria-stabilized zirconia (YSZ) is the industry standard material for thermal barrier coatings (TBC). However, it cannot meet the long-term requirements for advanced engines due to the phase transformation and sintering issues above 1200°C. In this study, we have developed a magnetoplumbite-type SrAl12O19 coating fabricated by atmospheric plasma spray, which shows potential capability to be operated above 1200°C. SrAl12O19 coating exhibits large concentrations of cracks and pores (~26% porosity) after 1000 hours heat treatment at 1300°C, while the total porosity of YSZ coatings progressively decreases from the initial value of ~18% to ~5%. Due to the contribution of porous microstructure, an ultralow thermal conductivity (~1.36 W m−1 K−1) can be maintained for SrAl12O19 coating even after 1000 hours aging at 1300°C, which is far lower than that of the YSZ coating (~1.98 W m−1 K−1). In thermal cyclic fatigue test, the SrAl12O19/YSZ double-ceramic-layer coating undertakes a thermal cycling lifetime of ~512 cycles, which is not only much longer than its single-layer counterpart (~163 cycles), but also superior to that of YSZ coating (~392 cycles). These preliminary results suggest that SrAl12O19 might be a promising alternative TBC material to YSZ for applications above 1200°C. 相似文献
19.
《Ceramics International》2022,48(22):33563-33570
Lanthanum hafnate (La2Hf2O7) with a pyrochlore structure has excellent high temperature stability and low thermal conductivity, which is promising for thermal/environmental barrier coatings (T/EBCs) applications. To reduce its thermal expansion coefficient (TEC) so as to better match SiCf/SiC composites, a smaller tetravalent dopant Ti4+ has been introduced in the Hf-sites to form La2(Hf1-xTix)2O7 (x ≤ 0.20). The phase composition and microstructure confirms that La2(Hf1-xTix)2O7 solid solutions possess a pure pyrochlore structure. With an increase of x, their TECs are decreasing consistently, whilst their thermal conductivities of La2(Hf1-xTix)2O7 are slightly increasing at high temperature but still much lower than those of meta-stable yttria partially stabilized zirconia, both of which are attributing to an increase of elastic modulus after Ti4+ doping on Hf-sites. The extremely excellent high temperature stability, relatively low thermal conductivities and low TECs suggest that La2(Hf1-xTix)2O7 is a prospective candidate material for T/EBC applications. 相似文献
20.
《Ceramics International》2016,42(9):11118-11125
Nanostructured 4SYSZ (scandia (3.5 mol%) yttria (0.5 mol%) stabilized zirconia) and 5.5 SYSZ (5 mol% scandia and 0.5 mol% yttria) thermal barrier coatings (TBCs) were deposited on nickel-based superalloy using NiCrAlY as the bond coat by plasma spraying process. The thermal shock response of both as-sprayed TBCs was investigated at 1000 °C. Experimental results indicated that the nanostructured 5.5SYSZ TBCs have better thermal shock performance in contrast to 4SYSZ TBCs due to their higher tetragonal phase content and higher fracture toughness of this coating 相似文献