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Article

Solid Particle Erosion Behavior of La2Ce2O7/YSZ Double-Ceramic-Layer and Traditional YSZ Thermal Barrier Coatings at High Temperature

by
Xianli Zhao
1,†,
Wei Liu
2,†,
Cong Li
2,3,
Gang Yan
2,
Qianwen Wang
2,
Li Yang
2,3,* and
Yichun Zhou
2,3,*
1
School of Materials Science and Engineering, Xiangtan University, Xiangtan 411105, China
2
School of Advanced Materials and Nanotechnology, Xidian University, Xi’an 710126, China
3
Frontier Research Center of Thin Films and Coatings for Device Applications, Academy of Advanced Interdisciplinary Research, Xidian University, Xi’an 710126, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Coatings 2022, 12(11), 1638; https://doi.org/10.3390/coatings12111638
Submission received: 9 October 2022 / Revised: 21 October 2022 / Accepted: 24 October 2022 / Published: 28 October 2022
(This article belongs to the Special Issue Thermal Barrier Coatings: Structures, Properties and Application)
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Abstract

:
Thermal barrier coatings (TBC) used for turbine blades are indispensable for the most advanced aero-engines due to their excellent thermal insulation performance. Solid particle erosion (SPE) at high temperatures is one of the most critical factors in TBC failure. The high-temperature SPE failure behavior of TBC on circular sheets and turbine blades was investigated in this paper at erosion angles 60° and 90°. The high-temperature thermal shock behavior of TBC was also studied as the control group. The SPE failure mechanism of TBC is attributed to the spallation and thickness decrease of TBC. The formation of thermally grown oxide is the main reason for the TBC spallation, while the thickness decrease of TBC is due to the impaction of solid particles by near-surface cracking. The erosion angle is critical to the failure behavior of TBC, and TBC is more susceptible to SPE at an erosion angle of 60° than that at 90° because of the additional shear stress. Furthermore, a La2Ce2O7/YSZ double-ceramic-layer TBC was designed and deposited on turbine blades. The experimental results indicate that this type of double-layer TBC has more excellent performance under SPE than traditional YSZ TBC.

1. Introduction

With the improvement of the thrust–weight ratio of aero-engines and the increase in turbine inlet temperature, higher and higher requirements for the performance of superalloy materials in the hot-end parts of aero-engines have been put forward. At present, the service temperature limit of advanced single-crystal nickel-based superalloys is 1150 °C, which obviously cannot meet the requirements of advanced aero-engines [1,2]. Thermal barrier coatings (TBC) on the turbine blade surface were considered as the most effective method to greatly improve the operating temperature of aero-engines due to its significant reduction of the blade surface temperature and the improvement of thermal efficiency of aero-engines [3,4,5,6,7,8,9]. However, the failure of TBC, especially the spallation of TBC from the blades in operating condition, is a major safety hazard for aero-engines. Therefore, the investigation of the failure mechanism of TBC has been a critical research topic in the field of TBC. The service environment of TBC is complex due to the diversity of thermal, mechanical, chemical, and other parameters, so the failure behavior of TBC is also complicated. Up to date, the failure mechanism of TBC in service has been divided into several aspects: the formation of thermally grown oxide (TGO) between the inner bond coat (BC) and the outer top ceramic coat (TC) [10,11], solid particle erosion (SPE) of TBC [12,13], and calcium-magnesium-aluminum-silicate (CMAS) corrosion of TBC [14,15,16].
When the aero-engine operates above desert areas or offshore marine environments, TBC can be damaged by SPE, which can seriously affect the lifetime of turbine components [17]. SPE is one of the most important factors in TBC failure and has attracted more and more attention in recent years. The research on the SPE behavior of TBC has been carried out in three main forms: theoretical research, numerical simulation, and experiments. In terms of theoretical research and numerical simulation, Ma et al. [18] have studied the effect of erosion angle on the crack propagation behavior of electron beam physical vapor deposition (EB-PVD) TBC under erosion by using the extended finite element method. Xiao et al. [19] have investigated the most critical factors in erosion damage of TBC on blade surfaces caused by SPE through numerical simulation. Yang et al. [20] studied the erosion behavior of EB-PVD TBC. They established the relationship between particle impact energy and the structural evolution of the TBC based on the finite element simulation method. In regards to experimental research, the work of Janos et al. [21] shows that adding polyester can reduce the erosion rate of YSZ TBC. Wellman et al. [22,23,24] have investigated the influence of ceramic layer morphology, columnar grains diameter, columnar grains dip angle, and aging and sintering treatment on the erosion behavior of EB-PVD TBC. In addition, a large number of researchers [25,26,27] have engaged in developing experimental equipment for erosion tests to simulate the blades’ service environment more realistically. However, the theoretical research and the current experimental work can hardly simulate the natural service environment of the aero-engine blades. Additionally, most of the experimental equipment used in the previous work is too simple to take into account thermal, mechanical, and chemical conditions simultaneously.
Therefore, in this paper, we independently developed a simulation device for a gas erosion environment with high temperature and high speed, which can simulate the SPE condition of the blades. NiCoCrAlY BC layer and Y2O3 stabilized ZrO2 (YSZ) TC layer were deposited on the circular sheets and model turbine blades. The SPE failure behavior of TBC-coated circular sheets and blades was studied under 1100 °C at the erosion angles of 60° and 90°. The effect of erosion angle on the SPE failure behavior was investigated. In order to improve the performance of TBC under SPE, a La2Ce2O7-YSZ double-ceramic-layer TBC was designed and deposited on the model blades. The development of A2B2O7 compounds, especially La2Ce2O7, is a hot topic in the research field of TBC [28,29,30] due to its high melting point, high-temperature phase stability, and excellent chemical corrosion resistance [31,32]. However, the thermal cycle life of single-layer LCO TBCs is short, and the coating flakes off extremely easily due to its low fracture toughness. The design of La2Ce2O7-YSZ double-layer TBC can effectively solve this problem. However, little work concentrates on the SPE behavior and SPE failure mechanism of La2Ce2O7-YSZ TBC. Thus, the SPE failure mechanism of La2Ce2O7-YSZ TBC was discussed in this paper based on the microstructural characterization after SPE treatment.

2. Materials and Methods

2.1. The Deposition of TBC

The substrate materials used in the current experiments were GH536 nickel-base superalloy circular sheets (diameter 30 mm and thickness 5 mm) and model turbine blades. Before coating deposition, all the samples were ground, polished, and treated by sandblasting. A NiCoCrAlY BC layer with a thickness of ~35 μm was first sprayed on the surface of the substrate by air plasma spraying (APS). After slightly polishing the BC layer surface, a 7–8 wt.% Y2O3 stabilized ZrO2 (YSZ) TC layer with thickness ~150 μm was deposited on NiCoCrAlY-coated circular sheets by electron beam physical vapor deposition (EB-PVD). YSZ TC layer was also deposited on NiCoCrAlY-coated turbine blades by plasma spray physical vapor deposition (PS-PVD). The La2Ce2O7-YSZ double-ceramic-layer TBC was also deposited by PS-PVD on the NiCoCrAlY-coated turbine blades. The thickness of BC layer and TC layer are typical values in the TBC system. BC layer with this thickness improves the oxidation resistance of the substrate and the adhesion property between the TC layer and the substrate. TC layer with this thickness provides thermal insulation.

2.2. SPE Test Equipment and Infrared Calibration Methods

Figure 1 shows the static service simulation device used for SPE tests of TBC. This device can be divided into the following main systems: (1) the feeding system, including nitrogen gas source, oxygen gas source, kerosene system, and powder feeder; (2) the mobile supersonic spray gun, which is the main part of the whole simulation device; (3) the sample platform, which is equipped with a cooling device for sample cooling; (4) test control system. During the SPE tests, kerosene was used as fuel and was mixed with oxygen in the pipeline. A high-temperature and high-speed flame flow mixed with solid particles was sprayed from the spray gun on the sample to simulate the SPE condition. The erosion angle between the flame flow and sample surface can be adjusted by rotating the sample holder. The SPE tests were conducted at the angles 90° and 60° between the flame flow and the sample surface to investigate the effect of erosion angle on the SPE behavior of TBC.
The temperature of the sample surface was measured by an infrared thermometer in the static service simulation device. The emissivity of the sample significantly influences the accuracy of temperature measurement by the infrared thermometer. The emissivity is not only related to the material but also to the temperature. Therefore, it is necessary to measure the emissivity of TBC before the SPE experiment to ensure the accuracy of the experimental temperature obtained by infrared thermometer. Figure 2 shows the primary process of infrared emission calibration by testing the temperatures at both sides of the sample by thermocouples A and B. Table 1 lists the infrared calibration data. Eventually, the emissivity of the sample was determined as 0.88 by calibration test.

2.3. Introduction of Powder Feeding Device and Particle Velocity Measurement

The powder feeder in this paper is type IGS-3W (Aigang, Zhengzhou, China), which can control the powder flow steadily and precisely. The powder feeder is shown in Figure 3 and mainly consists of two modules: the powder regulator and the powder storage tank. It also includes a powder regulator knob, a stirring regulator knob, and a gas flow meter. The upper interface of the gas flow meter is connected to the nitrogen gas through a pipe, and the lower interface is connected to the powder storage tank through a pipe to provide pressure for the storage tank. The powder storage tank is used to store the powder for experiments. Inside the tank, there is a stirring bar with a spiral tip to maximize its ability to stir the powder. The top of the bar is connected to an electric motor to provide power to stir the powder in the tank continuously. The speed of the stirring bar is controlled via a regulator stirring adjustment knob to meet the powder flow parameters required in this experiment. The powder adjustment knob on the powder regulator controls the speed of the motor below the powder storage tank to control the powder feed flow. The powder feeder works on the principle that nitrogen enters from the side of the powder reservoir and flows out of the top of the tank via a nitrogen passage rod in the tank. Under the action of the motor and stirring rod, the powder in the reservoir enters the powder feeder pipeline in a steady and precise manner. It is eventually ejected with the flame stream of the gun onto the surface of the sample.

2.4. Experimental Test Procedure

The whole SPE test process is as follows: (1) clamp the coated sample (how the circular sheet sample was clamped is shown in Figure 4); (2) shock the sample with solid particles mixed with high-temperature and high-speed flame flow; (3) turn off the flame spray gun when the temperature of sample surface reaches 1100 °C and is maintained for 120 s; (4) cool down the sample in the external environment for 130 s; (5) repeat step (3) and step (4) until the peeling area of the coating is larger than 10% of the sample surface area; (6) stop the test. Figure 5 shows the temperature curve of the sample surface measured by an infrared thermometer during the SPE test. In order to figure out the influence of high-temperature SPE on the cyclic life of TBC, a series of control experiments were designed and conducted in this study, in which the samples were only subjected to thermal shock at high temperatures without erosion.

2.5. Macroscopic Morphology and Microstructural Characterization

During the whole experimental process, one picture was taken every ten cycles to check the coating’s erosion condition and macroscopic morphology evolution. Scanning electron microscopy (SEM, TESCAN MIRA, TESCAN, Brno-Kohoutovice, Czech Republic) equipped with an energy-dispersive spectrometer (EDS, Oxford, Oxford, UK) was used to characterize the TBC’s surface and cross-sectional microstructure.

3. Results and Discussions

3.1. The SPE and Thermal Shock Behavior of the TBC-Coated Circular Sheets

3.1.1. Surface Macroscopic Morphology Evolution of TBC

Figure 6 shows the macroscopic photos of the TBC-coated circular sheets after high-temperature SPE tests for different cycles at an erosion angle of 90°. After 120–360 cycles (Figure 6b–e), the thickness of TBC on samples significantly decreases with test cycles, and coating spallation occurs at the edge regions of the circular sheets. With the increase in erosion cycles to 375 (Figure 6f), in addition to the edge regions, two spallation areas appear on the inner side of the sample surface (see inside the red circles). This type of surface spallation is caused by the continuous particle erosion of the sample. The calculation results indicate that the surface peeling area has reached 10% of the whole surface area, and as a result, it can be determined that the TBC has failed.
When the erosion angle is 60°, as shown in Figure 7, the surface macroscopic morphology evolution behavior of TBC under SPE is similar to that at an erosion angle of 90°. The sample edge peeling and the TBC thickness decrease occur. However, two apparent differences can be observed between these two tests at different erosion angles: (1) the service life of TBC at an erosion angle of 60° is 280 cycles, which is much smaller than that of 375 cycles at an erosion angle of 90°, and this indicates the angle between the flame beam and the surfaces of samples can significantly affect the SPE behavior of the TBC; (2) the TBC spallation only occurs at the edge region of the sample, which it should, because the spallation area at the edge region has reached 10% of the whole surface area before the occurrence of the spallation on the inner surface region. In other words, the TBC has failed before the spallation of TBC on the inner surface occurs.
For comparison with the SPE tests of the TBC-coated samples, when the samples only suffered thermal shock, the service life of the TBC increased to 505 cycles and 400 cycles at the impact angles of 90° and 60°, respectively. The macroscopic morphology evolution results during thermal shock are shown in Figure 8 (impact angle 90°) and 12 (impact angle 60°). The failure mechanism of TBC under thermal shock is quite different from that under SPE. When only suffering thermal shock, on the one hand, the coating spallation occurs at the edge region of the circular sheet (Figure 8c–f and Figure 9b–f); on the other hand, the TBC thickness decrease at the inner surface can hardly be observed. These results reveal that SPE can effectively impact TBC’s thickness evolution and failure behavior. The effect of impact angle on the service life of TBC in these tests can also be summarized as follows: the smaller the impact angle, the shorter the service life of TBC.

3.1.2. Surface Microstructures of the TBC

Figure 10 shows the surface SEM micrographs of the as-deposited TBC and TBC after a failure during SPE and thermal shock tests on circular sheets. As shown in Figure 10a, the EB-PVD TBC shows a typical columnar grain structure. After high-temperature SPE (Figure 10b,c) and thermal shock tests (Figure 10d,e), the surface morphology of EB-PVD TBC has become quite different from the original morphology. The columnar grains can hardly be discerned, and the surface is no longer smooth. Spherical particles can be observed on the surfaces of samples after SPE tests (Figure 10b,c), which should be the alumina erosion particles. When comparing the surface microstructures after tests at angles 90° (Figure 10b,d) and 60° (Figure 10c,e), there are no significant changes, and the surface morphologies are almost the same.

3.1.3. Cross-Sectional Microstructures of TBC

Figure 11 shows the cross-sectional microstructures of the as-deposited TBC and TBC after failure in the SPE and thermal shock tests on circular sheets. As shown in Figure 11a, the as-deposited EB-PVD TBC shows a typical columnar structure without thermally grown oxides (TGO) at the interface between the YSZ TC and the MCrAlY BC. This type of columnar grains is consistent with the surface SEM results in Figure 10. After high-temperature SPE tests (Figure 11b–d) and thermal shock tests (Figure 11e,f), a thin TGO layer formed at the YSZ/MCrAlY interface, which indicates the oxidation of the MCrAlY BC layer. Based on Figure 11c, with a higher magnification at the local region of Figure 11b, after SPE tests at an angle of 90°, many transverse cracks (indicated by yellow arrows) are distributed inside the YSZ grains close to the top surface, and these cracks have divided the columnar grains into several segments. The broken columnar grains should be the reason for the decrease in TBC thickness under the effect of high-temperature SPE. The sample’s microstructure after SPE tests at an angle of 60° (Figure 11d) shows a similar failure mode to that at an angle of 90°. However, when only suffering thermal shock without erosion (Figure 11e,f), horizontal cracks can be observed at the YSZ/TGO interface (indicated by yellow arrows), which can significantly affect the binding force between the outer TC layer and the inner BC layer. The formation of this type of crack should be the failure mechanism of the TBC under thermal shock tests. It is the growth of TGO that led to the formation of cracks between the TC layer and the BC layer.

3.1.4. The Failure Mechanism of TBC during the SPE Tests

There is no doubt that the spallation of TBC at the edge regions of the circular sheets is the most crucial reason for the TBC failure under thermal shock tests and SPE. However, when suffering SPE, thickness decrease of TBC under erosion is another critical factor in TBC failure. Three types of erosion failure mechanisms of TBC can be summarized based on the ratio between the particle diameter D and the grain width d of the columnar grains [33,34,35]: type I, mild erosion by near-surface cracking; type II, compaction damage mode, in which a dense zone forms under the particle impacts; type III, in which severe erosion by foreign object damage and large-scale plastic deformation occurs. In the current work, small transverse cracks are distributed inside the columnar grains near the outer surface of TBC. Therefore, the failure mechanism should follow the type I mode. The erosion particles used in the current work are too small to form a continuous dense layer inside the YSZ. Then, bending waves can be induced on the columnar grains close to the top surface, and cracking across the columnar grains can be further induced by the bending waves. Eventually, the SPE causes the detachment of the top side of the columnar grains, and the thickness of the TBC gradually decreases. When the erosion angle is 90°, the columnar grains are only subjected to compressive stress perpendicular to the surface by high-temperature gas and particle impact. However, transverse shear stress will be introduced on the columnar grains at an erosion angle of 60°. The shear stress is the main reason the TBC is more prone to failure at an erosion angle of 60°.

3.2. The SPE Behavior of the TBC-Coated Turbine Blades

Figure 12 shows the macroscopic photos of the TBC-coated turbine blades before and after high-temperature SPE tests at an erosion angle of 60°. When the erosion angle is 60°, the flame mainly impacts the leading edge and the blade’s concave surface, while the blade’s convex surface rarely suffers high-temperature erosion. It can be seen in Figure 12a that the surface of TBC-coated turbine blades was smooth before the SPE test. With the increase in the test cycles, dark spots can be observed on the leading edge and concave surface (indicated by the yellow arrows in Figure 12e), which should mainly be the incompletely burned fuel gas aviation kerosene. Aviation fuel contains impurities, and when these impurities are not entirely burned, there will be dark spots formed on the blade’s surface.
Moreover, most of the dark spots are located on the maximum curvature regions of the pressure surface. When the SPE test reaches 200 cycles (Figure 12c), the coating surface is no longer smooth, and erosion pits appear obviously, especially on the leading edge (inside the red circle). This phenomenon is due to the long-term erosion of particle impaction under the high-temperature and high-speed flame. After 320 (Figure 12d) and 380 cycles (Figure 12e), TBC spallation occurs on the top position of the leading edge. As the SPE cycle increases, the length of the crack rapidly increases. After 420 cycles (Figure 12f), the length of the coating spallation increases to 10 mm. The TBC failure is defined as the crack length on the coating exceeding 10 mm or the area of TBC spallation exceeding 10% of the blade surface. Therefore, after 420 cycles, the TBC fails and the test is stopped. According to the SPE failure behavior of the blades, the leading-edge region is the most susceptible area, and the TBC spallation at the leading-edge region can lead to TBC failure during the SPE tests.

3.3. The SPE Behavior of the La2Ce2O7-YSZ Double-Layer TBC

A double-ceramic-layer TBC with outer La2Ce2O7 and inner YSZ was designed and deposited on turbine blades. The same high-temperature SPE tests were conducted on the La2Ce2O7-YSZ double-layer TC with inner NiCoCrAlY BC. The result shows that this La2Ce2O7-YSZ double layer has a much longer service life (900 cycles) than single-layer YSZ TBC (420 cycles). Figure 13 and Figure 14 show the cross-sectional microstructures of TBC on four typical regions and EDS maps of the trailing-edge region of turbine blades after SPE tests at an angle of 60°, respectively.
The failure of the TBC is caused by two factors: the spallation of the outer ceramic TC layer and the thickness decrease of the TC layer. After SPE, the TC spallation was only observed on the leading-edge region (Figure 13a) of the blade, and this phenomenon is consistent with the SPE behavior of the YSZ single-layer TBC on blades in Figure 14e,f. The spallation of TC is mainly due to the formation and growth of the TGO layer at the TC/BC interface. A TGO layer with a thickness of ~4.51 μm formed on the leading-edge region (Figure 13a), which is much thicker than that on the other regions of the blade (Figure 13b–d). The formation and growth of TGO can introduce thermal mismatch stress at the TC/BC interface, which results in the formation and expansion of cracks at the interface (see Figure 13a) and eventually leads to the spallation of the outer ceramic TC. According to the cross-sectional EDS maps of the trailing-edge region in Figure 14, the Al element is enriched inside the TGO layer at the TC/BC interface. This phenomenon indicates that the content of the TGO layer should mainly be Al2O3. The thickness of the TC layer significantly decreases after SPE tests because of the erosion effect of the hard particles. Compared with the TBC on the convex (Figure 13b) and concave (Figure 13c) surfaces, the outer La2Ce2O7 layers of TBC are much thinner on the leading-edge (Figure 13a) and trailing-edge (Figure 13d) regions of blades. This phenomenon indicates that in addition to the leading-edge region, the trailing-edge region is also more susceptible than the convex and concave surfaces of the blades.
The performance of La2Ce2O7-YSZ double-layer TBC under high temperature is more excellent than the conditional single-layer YSZ TBC. Firstly, the thermal expansion coefficient (CTE) of La2Ce2O7 (11.21 × 10−6 K−1) is higher than YSZ (11.08 × 10−6 K−1) at 1100 °C [36], and its CTE is close to the MCrAlY BC layer (13–15 × 10−6 K−1) [37], so the La2Ce2O7-YSZ double-layer TBC can match the metal substrate better at high temperature. Secondly, the thermal conductivity of La2Ce2O7 is significantly smaller than YSZ [38]. Therefore, the temperature at the TC/BC interface of the La2Ce2O7-YSZ double-layer coating should be much lower than that of the YSZ single-layer coating. On the one hand, the growth rate of TGO should be lower at low temperatures; on the other hand, the thermal stress mismatch at TC/BC interface should be smaller. Thirdly, La2Ce2O7 has better mechanical properties at high temperatures [39,40]. All the results by other researchers indicate that the La2Ce2O7-YSZ double-layer TBC shows better thermal shock and thermal cycling resistance than single-layer YSZ TBC [36,40].

4. Conclusions

The high-temperature SPE failure behavior of the TBC on circular sheets and model turbine blades was investigated in this paper. The failure mechanism was discussed. An La2Ce2O7-YSZ double-ceramic-layer TBC was designed and prepared to improve the SPE resistance of the TBC. Several critical conclusions can be drawn:
  • For TBC on circular sheet samples, the SPE failure of TBC is mainly attributed to the TBC spallation at the edge regions and the thickness decrease of TBC caused by particle erosion. TBC spallation at the edge regions is the only reason for TBC failure. High-temperature SPE is more harmful to TBC compared with thermal shock when only suffering the thermal shock.
  • TBC is more prone to fail at an angle of 60° during the SPE and thermal shock tests than at an angle of 90°. This is because transverse shear stress can be conducted on the columnar grains of TBC at an angle of 60°.
  • The La2Ce2O7-YSZ double-layer TBC shows better SPE resistance than single-layer YSZ due to its excellent thermodynamic and mechanical properties at high temperatures.
  • The failure mechanism of the TBC under SPE in the current work follows the type I mode: mild erosion by near-surface cracking.

Author Contributions

X.Z.: Experiment, Data curation, Writing—original draft. W.L.: Experiment, Data curation, Writing—original draft. C.L.: Funding acquisition, Writing—review and editing. G.Y.: Methodology, Investigation, Writing—review and editing. Q.W.: Methodology, Investigation. L.Y.: Funding acquisition, Writing—review and editing. Y.Z.: Funding acquisition, Writing—review and editing. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China grant number 11890684 and 52102142, the Foundation for Innovative Research Groups of Hunan Province grant number 2020JJ1005, and the Innovation Capability Support Program of Shaanxi program number 2022TD-28.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Figure 1. Schematic diagram of the solid particle erosion test equipment.
Figure 1. Schematic diagram of the solid particle erosion test equipment.
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Figure 2. Schematic diagram of infrared emissivity calibration process.
Figure 2. Schematic diagram of infrared emissivity calibration process.
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Figure 3. Photo of powder feeder system.
Figure 3. Photo of powder feeder system.
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Figure 4. Photo of sample clamping method during the SPE test.
Figure 4. Photo of sample clamping method during the SPE test.
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Figure 5. Temperature control curve during SPE tests of TBC.
Figure 5. Temperature control curve during SPE tests of TBC.
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Figure 6. Surface macroscopic photos of the TBC before and after SPE for different cycles at the erosion angle of 90°. (a) As-deposited samples; (b) 120 cycles; (c) 240 cycles; (d) 300 cycles; (e) 360 cycles; (f) 375 cycles.
Figure 6. Surface macroscopic photos of the TBC before and after SPE for different cycles at the erosion angle of 90°. (a) As-deposited samples; (b) 120 cycles; (c) 240 cycles; (d) 300 cycles; (e) 360 cycles; (f) 375 cycles.
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Figure 7. Surface macroscopic photos of the TBC after SPE for different cycles at the erosion angle of 60°. (a) As-deposited samples; (b) 60 cycles; (c) 120 cycles; (d) 180 cycles; (e) 240 cycles; (f) 280 cycles.
Figure 7. Surface macroscopic photos of the TBC after SPE for different cycles at the erosion angle of 60°. (a) As-deposited samples; (b) 60 cycles; (c) 120 cycles; (d) 180 cycles; (e) 240 cycles; (f) 280 cycles.
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Figure 8. Surface macroscopic photos of the TBC after thermal impacts for different cycles at the impact angle of 90°. (a) 5 cycles; (b) 100 cycles; (c) 200 cycles; (d) 300 cycles; (e) 400 cycles; (f) 505 cycles.
Figure 8. Surface macroscopic photos of the TBC after thermal impacts for different cycles at the impact angle of 90°. (a) 5 cycles; (b) 100 cycles; (c) 200 cycles; (d) 300 cycles; (e) 400 cycles; (f) 505 cycles.
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Figure 9. Surface macroscopic photos of the TBC after thermal impacts for different cycles at the impact angle of 60°. (a) 10 cycles; (b) 100 cycles; (c) 200 cycles; (d) 300 cycles; (e) 350 cycles; (f) 400 cycles.
Figure 9. Surface macroscopic photos of the TBC after thermal impacts for different cycles at the impact angle of 60°. (a) 10 cycles; (b) 100 cycles; (c) 200 cycles; (d) 300 cycles; (e) 350 cycles; (f) 400 cycles.
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Figure 10. Surface microstructure of TBC before and after tests on circular sheets: (a) as-deposited sample; (b) after SPE at angle 90°; (c) after SPE at angle 60°; (d) after thermal shock at angle 90°; (e) after thermal shock at angle 60°.
Figure 10. Surface microstructure of TBC before and after tests on circular sheets: (a) as-deposited sample; (b) after SPE at angle 90°; (c) after SPE at angle 60°; (d) after thermal shock at angle 90°; (e) after thermal shock at angle 60°.
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Figure 11. Cross-sectional microstructure of TBC before and after tests on circular sheets: (a) the as-deposited TBC; (b) after SPE at angle 90° at low magnification; (c) after SPE at angle 90° at high magnification; (d) after SPE at angle 60°; (e) after thermal shock at angle 90°; (f) after thermal shock at angle 60°.
Figure 11. Cross-sectional microstructure of TBC before and after tests on circular sheets: (a) the as-deposited TBC; (b) after SPE at angle 90° at low magnification; (c) after SPE at angle 90° at high magnification; (d) after SPE at angle 60°; (e) after thermal shock at angle 90°; (f) after thermal shock at angle 60°.
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Figure 12. Surface macroscopic photos of the TBC-coated turbine vanes before and after high-temperature SPE tests at an erosion angle of 60°. (a) As-deposited; (b) 60 cycles; (c) 200 cycles; (d) 320 cycles; (e) 380 cycles; (f) 420 cycles.
Figure 12. Surface macroscopic photos of the TBC-coated turbine vanes before and after high-temperature SPE tests at an erosion angle of 60°. (a) As-deposited; (b) 60 cycles; (c) 200 cycles; (d) 320 cycles; (e) 380 cycles; (f) 420 cycles.
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Figure 13. Cross-sectional SEM micrographs of TBC on four typical regions of turbine blades after SPE at angle 60°: (a) leading-edge region; (b) convex surface of the blade; (c) concave surface of the blade; (d) trailing-edge region.
Figure 13. Cross-sectional SEM micrographs of TBC on four typical regions of turbine blades after SPE at angle 60°: (a) leading-edge region; (b) convex surface of the blade; (c) concave surface of the blade; (d) trailing-edge region.
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Figure 14. Cross-sectional SEM micrograph and EDS maps of La, Ce, Zr, Y, Cr, and Al of TBC on the trailing-edge region.
Figure 14. Cross-sectional SEM micrograph and EDS maps of La, Ce, Zr, Y, Cr, and Al of TBC on the trailing-edge region.
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Table
Table 1. Infrared calibration data.
Table 1. Infrared calibration data.
Measurement NumberTemperature of Thermocouple A (°C)Temperature of Thermocouple B (°C)Emissivity
1110110980.89
2110010970.88
3110110990.87
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Zhao, X.; Liu, W.; Li, C.; Yan, G.; Wang, Q.; Yang, L.; Zhou, Y. Solid Particle Erosion Behavior of La2Ce2O7/YSZ Double-Ceramic-Layer and Traditional YSZ Thermal Barrier Coatings at High Temperature. Coatings 2022, 12, 1638. https://doi.org/10.3390/coatings12111638

AMA Style

Zhao X, Liu W, Li C, Yan G, Wang Q, Yang L, Zhou Y. Solid Particle Erosion Behavior of La2Ce2O7/YSZ Double-Ceramic-Layer and Traditional YSZ Thermal Barrier Coatings at High Temperature. Coatings. 2022; 12(11):1638. https://doi.org/10.3390/coatings12111638

Chicago/Turabian Style

Zhao, Xianli, Wei Liu, Cong Li, Gang Yan, Qianwen Wang, Li Yang, and Yichun Zhou. 2022. "Solid Particle Erosion Behavior of La2Ce2O7/YSZ Double-Ceramic-Layer and Traditional YSZ Thermal Barrier Coatings at High Temperature" Coatings 12, no. 11: 1638. https://doi.org/10.3390/coatings12111638

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