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Article

Microstructure and Cracking Behavior of a Four-Layer Thermal Barrier Coating After Thermal Cycle Test

by
Xuyang Wang
1,2,
Yanna Cui
2,
Yang Zhou
2,*,
Yuzhu Zhao
1 and
Jun Wang
2,*
1
Steam Turbine and Gas Turbine Technology Department, Huadian Electric Power Research Institute Co., Ltd., Hangzhou 310030, China
2
School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
*
Authors to whom correspondence should be addressed.
Coatings 2025, 15(3), 307; https://doi.org/10.3390/coatings15030307
Submission received: 25 January 2025 / Revised: 4 March 2025 / Accepted: 4 March 2025 / Published: 6 March 2025
(This article belongs to the Special Issue Advances of Ceramic and Alloy Coatings, 2nd Edition)
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Abstract

:
Microstructure evolution and cracking behavior of a four-layer thermal barrier coating (TBC) with double YSZ layers during thermal cycle tests were studied in the current work. The temperature range of the thermal cycle test ranged from room temperature to 1100 °C under atmospheric conditions. The TBC consisted of tetragonal t′ and t phases as well as monoclinic yttrium oxide. After 500 thermal cycles, the m-ZrO2 phase was formed through the phase transformation from t′-ZrO2 to m-ZrO2 and c-ZrO2. A large number of bulk thermally grown oxides (TGO), including chromium, spinel, and yttrium aluminates, were formed around pores in the transition layer (TL). Furthermore, the thickness of the TGO layer increased with a relatively low increase rate during the test (where kp was about 0.17 μm2/h). This may be attributed to the formation of bulk TGO around pores within the TL, which could consume some of the oxygen. The results show that large horizontal cracks are likely to form at the TSL/TIL and TIL/TL interfaces, while vertical cracks tend to occur near the surface of the TSL, and the propagation rate is relatively low. The propagation of horizontal cracks is the primary cause of failure in this four-layer structure. After the thermal cycle test, the porosity of TSL decreased significantly, from 7.17% to 0.76%. The results in this study may help optimize the design and preparation of TBCs with double YSZ layers.

1. Introduction

Gas turbines have become one of the important power devices in the energy sector due to their high efficiency and low emissions [1,2,3]. Gas temperature is an important indicator of the technological level of heavy-duty gas turbines [4]. TBC systems have played an important role in isolating hot components from high temperature, protecting the superalloys by reducing their service temperatures [5,6,7]. TBCs are typically multilayered systems comprising ceramic top coats (TC), thermally grown oxides (TGO), bond coats (BC) and substrates [8,9,10].
Currently, yttria partially stabilized zirconia (7–8 wt.% Y2O3-ZrO2) is the most widely used material for TC [11,12]. However, under high temperature, phase transformations are inevitable in TBCs [13]. In addition, ceramic sintering at high temperatures is another problem, as it can lead to grain growth and porosity reduction, diminishing thermal insulation performance and cracking resistance [14,15]. To improve the performance of the TBCs, a double-ceramic-layer (DCL) TBC system was proposed [16,17]. M. Han et al. [18] investigated the effects of the interface shape on the stress distribution of DCL TBCs. The research results indicate that the shapes of the interfaces only affect the stress of the adjacent regions in the thickness direction. Under service conditions, oxygen diffuses through the porous TC and reacts with the BC, leading to the thickening of the TGO layer. Research shows that the thickness of the TGO layer directly affects the service life of the coating [19,20]. W.S. Li et al. [21] numerically studied the failure mechanisms of DCL TBCs and found that the inelastic deformation is the intrinsic cause of cracking near TGO. Thermal cycle test is an effective method to study the service performance and failure mechanisms of DCL TBCs. K.H. Yang et al. [22] investigated the failure mechanism of atmospheric plasma sprayed (APS) (Gd, Yb) doped yttria-stabilized zirconia (YSZ) DCL TBCs by continuous thermal cycle at 1500 °C.
The DCL TBCs, based on La2Zr2O7 (LZO)/YSZ and Gd2Zr2O7 (GZO)/YSZ, have been extensively investigated [23,24]. However, although TBCs with double YSZ layers have been designed for 130 MW gas turbine first-stage blade [25], there is still a lack of studies on microstructure stability and failure mechanism. In this study, a thermal cycle test was conducted to simulate the start–stop processes of gas turbines, their microstructure change, as well as their mechanisms of crack initiation and growth in the TBC based on the double YSZ layers investigated.

2. Methodology

Electron beam physical vapor deposition (EB-PVD) and atmospheric plasma spraying (APS) are two primary methods for preparing ceramic coatings. In addition to the APS, high-velocity oxygen fuel spray (HVOF) is also a common method for preparing the BC.
The TBC system adopted in this study is designed with a four-layer structure consisting of a TBC smooth layer, a TBC inner layer, a transition layer, and a bottom layer (BL). The substrate is a nickel-based superalloy (Cannon-Muskegon GTD111), and the composition was detected using the Thermo ARL—ARL 4460 Optical Emission Spectrometer (Thermo Scientific, Waltham, MA, USA), whose main composition is shown in Table 1. The BL was sprayed using HVOF with Amdry 9954 powder (Co32Ni21Cr8Al0.5Y). The TL was sprayed using APS with Amdry 962 powder (Ni22Cr10Al1Y). After the TL was sprayed, a vacuum solution-aging heat treatment was conducted. APS was used for TIL with Amdry 204NS-1 powder (8Y2O3-ZrO2). The TSL of the thermal barrier coating was sprayed using APS with Amdry 204F powder (8Y2O3-ZrO2). HVOF spraying utilized the CN-S14015J MultiCoat HVOF-GF spraying equipment from OERLIKON Company. APS spraying employed an OERLIKON spraying system, which included the MultiCoat APS core equipment and the ABB IRB2600 robot for the spray gun support mechanism. The detailed preparation process of the TBC in this study is described in Ref. [25].
The thermal cycle test was performed on a coated specimen (4 × 4 cm2). The sample was heated from room temperature to 1100 °C in a preheated furnace, held at 1100 °C for 50 min, and then the TBC surface temperature fan-cooled down to below 200 °C for 10 min. The temperature was controlled by a K-type thermocouple. The test was stopped after 500 cycles. The schematic diagrams of the thermal cycle test setup and the sample temperature under a single thermal cycle are shown in Figure 1a,b.
The microstructures were analyzed using scanning electron microscopy (SEM, Zeiss Sigma 500) in back-scattered electron (BSE) mode. The chemical composition analysis was performed using energy dispersive spectroscopy (EDS) equipped in the SEM. Due to the poor conductivity of the ceramic thermal barrier coating, a gold sputtering treatment was performed prior to the SEM analysis. The phases of the as-sprayed state and thermal cycle test samples were determined using X-ray diffraction (XRD), and the XRD data were obtained using a diffractometer (D8 ADVANCE Da Vinci). To evaluate the bonding performance of TBC in this study, a bond strength test was performed using the ASTM C 633-13 method on coated GTD 111 samples. Figure 2 illustrates a schematic diagram of the bond strength test. The epoxy used in the test is FM 1000, Lot# 6349-0005. The specimens were cylindrically shaped for the bond strength tests and the diameters of the samples were 25.30 mm and 24.97 mm, respectively. The crosshead speed was 1.016 mm/min. In addition to the bond strength tests, a reference test was also conducted. In the reference test, there was only epoxy between the pulling fixture and parent metal (superalloy), and the result demonstrated the strength of the adhesive (FM1000). Nano-indentation tests were performed on the cross-sections in the samples of the as-sprayed state, and after the cycle test, ten points were randomly selected in the cross-section of TSL for each test using a nanoindenter (Femtotool FT104).

3. Results and Discussion

3.1. Phase Composition of the As-Sprayed Sample

Figure 3 presents the X-ray diffraction pattern of the as-sprayed coating. According to the Joint Committee on Powder Diffraction Standards (JCPDS) data (no. 44-0399 for monoclinic yttrium oxide, no. 81-1544 for tetragonal zirconia), the TBC consists of a mixture of tetragonal zirconia and monoclinic yttrium oxide phases (Figure 1a). Figure 1b shows an enlarged image of the range from 72° to 76°, where the metastable tetragonal t′ phase is detected. The t′ phase forms through rapid solidification (106–107 K/s), while the t phase originates from unmelted powders during spraying [26].

3.2. Microstructure of TBC Before Thermal Cycle Test

Figure 4a shows the structure of the cross-section of the TBC. The ceramic layer had typical layered structure characteristics. The average thickness of the BL, TL, TIL, and TSL were 201.5 μm, 83.6 μm, 107.5 μm, and 421.6 μm, respectively. The TIL and TSL exhibited porous microstructures with pores, splat boundaries, and microcracks. This porous morphology was mainly because of the insufficient melting of the spraying powders during the process, which underwent slight and inadequate deformation after striking the substrate. Consequently, some carrier gas was retained, creating pores of varying sizes in the TBC. Molten powders in the plasma flame impacted the substrate or previously deposited TBC, becoming flattened and stacked to form a dense surface with minimal porosity [27]. Fine spherical pores homogeneously were distributed, as seen in Figure 4a, which were derived from entrapped gas within the molten droplets generated during the grinding and polishing steps. The ceramic layers contained numerous non-bonded splat interfaces and cracks, which resulted from the partially melted powders [28]. The porosities of TIL and TSL were 6.59% and 7.17%, respectively. From the result of the finite element calculation [29], the pores in the ceramic layer could alleviate stress concentration and benefit the performance of TBCs. A rough interface in the coating system could improve the adhesion and seemingly increase the lifetime.
As can be seen from the enlarged cross-sectional image of the TIL in Figure 4b, several splats were divided into several segments by cracks. During the thermal spray process, the powders were first melted and accelerated, after which they impacted the substrate at high speeds and formed liquid films. These liquid films solidified into solid splats, and tensile stress developed in the splats due to thermal shrinkage during cooling. The shrinkage would be limited due to the high bonding strength between splats. As the shrinkage stress increased, cracks occured and divided the film into smaller domains because of the low plasticity. The inter-splat cracks in Figure 4b resulted from the discontinuous stacking of the molten powders and substrate thermal unbalance during the spraying process. Z.Y. Wei et al. [30] pointed out that although inter-splat pores and intra-splat cracks could release some of the stress, significant stress still remains in the bonding area between the splats in the as-sprayed TBC. Residual stress plays a crucial role in the strain tolerance of TBCs, affecting the coating’s thermal crack propagation, cycling stability, and adhesion.
Figure 5 shows the SEM-BSE image of the TL, where there is a thin TGO layer between the TIL and TL and the thickness is about 0.55 µm. The BL comprises a continuous γ phase and β precipitates, showing a typical two-phase microstructure [31].
Elemental maps for the region in Figure 4a were acquired and presented in Figure 6. From the aluminum and oxygen distribution images, area B in Figure 4a is aluminum oxide instead of a pore. The elemental distribution of TIL and TSL remained identical because the composition of the powders used for spraying was the same. Ni content in TL was significantly higher than that in BL, while Co content in BL was significantly higher than that in TL. These elemental distributions were essentially consistent with the elemental composition of the powders used for spraying the different layers.

3.3. Bond Strength of the TBC

The results of the bond strength tests are presented in Table 2. The bond strengths of the samples were 76.7 MPa and 70.8 MPa, respectively. Additionally, the strength of the adhesive (FM1000) was 84.9 MPa (Table 2). The sample labeled "Blank" in Table 2 represents the reference test, demonstrating the strength of the adhesive. As reported from a recent study [32], the bond strength of an electron beam physical vapor deposition (EB-PVD) (Yb0.1Gd0.9)2Zr2O7 (YbGdZrO) TBC was about 63.05 MPa for the as-deposited state, and the TBC exhibited excellent thermal shock properties.

3.4. Phase Composition of the TBC After Thermal Cycle Test

After 500 thermal cycles at 1100 °C, in addition to the t-ZrO2 phase and Y2O3, a small amount of m-ZrO2 phase was also detected in the ceramic layer after thermal cycling (Figure 7). According to previous studies [33,34], the m-ZrO2 phase was transformed through the phase transition of t′-ZrO2 to m-ZrO2 and c-ZrO2 during the thermal cycle test.
The thermal expansion coefficients of m-ZrO2 phase were significantly different from those of the tetragonal t and t′ phases (approximately 5% volume change) [35], which could cause crack initiation and propagation, shortening the service life of the TBC [36].

3.5. Microstructure of TBC After Thermal Cycle Test

After 500 thermal cycles, no spallation occurred, and the TBC remained intact. Figure 8 shows the cross-section of the TBC after the thermal cycle test. The interfaces between layers have become less clear compared to those before the thermal cycle test. The porosity of the TSL was 0.76%. The porosity reduction was due to ceramic sintering at high temperatures, which led to a decline in thermal insulation performance. As sintering progressed, the tetragonal phase in the YSZ ceramic decreased, resulting in an increase in elastic modulus and a decrease in cracking resistance [35].
The TGO layer between TIL and TL was about 4 µm in thickness after 500 thermal cycles. In addition, bulk TGO appeared to form within TL beneath the interface, unlike in previous research, where they were mainly presented as a layer on the surface of TL. From the magnified image (Figure 8b), it can be seen that these regions were always accompanied by pores within them. In the as-sprayed state, the porosity of the transition layer was 6.58% (derived from Figure 4a), with numerous pores distributed throughout, which could provide a pathway for oxygen ingress. As a result, bulk TGO formed around pores beneath the IL/TL interface, which is consistent with A. Rabiei’s study [31]. According to EDS analysis (Table 3), the bulk TGO primarily consisted of alumina and a small amount of nickel oxide (site A). In some locations, domains with a lighter gray contrast were adjacent to the bulk TGO. From the EDS results, it can be seen that they were typically spinel (comprising oxides of Cr/Ni/Co) (site B) and yttrium aluminates (site C), which is consistent with Chen’s research [37]. The relationship between TGO thickness (δ) and time at high temperature (t) at 1000 °C can be described as [38]:
δ2 = kp·t,
where kp is a fitting constant and equals to about 0.17 μm2/h in this study. In this study, the initial thickness of the TGO was 0.55 μm, and the approximate estimated value of Kp was 0.038 μm2/h for 1100 °C. It can be speculated that the formation of the bulk oxides may have reduced the growth rate of the TGO layer, and the crack evolution in TBCs depended crucially on the thickness of the TGO layer [39]. It is generally accepted that thicker TGO layers result in greater accumulated growth stress, which, in turn, leads to a shorter life of TBCs [21]. Therefore, the formation of bulk TGO may extend TBC life.
The formation of spinel results from the depletion of aluminum with concurrent enrichment of the oxide by Cr, Co and Ni. From Table 3, it can be seen that the contents of Al, Cr, and Co elements in the TL (site D) were 8.02 at.%, 24.29 at.%, and 17.73 at.%, respectively. Compared to the as-sprayed state, the Al content slightly decreased, while the Cr content changed in the opposite direction. In addition, Co element (17.73 at.%) was detected in TL, which originated from diffusion from BL during the vacuum solution aging heat treatment and thermal cycling. As shown in Figure 8b, although a large number of mixed oxides appeared in the TL, no cracks were found in this layer. This might have been due to the similar thermal expansion coefficient of the mixed oxides to that of the TL [32], which allowed for coordinated deformation between the oxides and the TL during the thermal cycle test. Therefore, although oxides appeared during the thermal cycle test, cracks did not form within the TL.
Many cracks appeared in the microstructure after the thermal cycle test. Several cracks appeared in the region near the TIL. The crack pointed to by the red arrow (Crack I) in the TBC layer was approximately 395 μm from the substrate surface at the right boundary of Figure 8a, indicating that the TIL/TSL interface was the crack initiation location. It is worth noting that this crack did not propagate along the interface; it gradually propagated from the boundary into the TIL until it reached the TL. Although the critical stress for TGO was much higher than that for TBC [40,41], such cracks could penetrate through the TGO (Crack II, pointed to by the blue arrow in Figure 8a). According to B. Li’s study [14], the formation of cracks near the interface of the ceramic layers in the LZ/YSZ type DCL TBCs was caused by the thermal expansion mismatch. In this study, the double ceramic layers were sprayed using YSZ powders with different sizes, resulting in varying porosity levels. Therefore, porosity should be considered an important factor, as it affects the thermal expansion rate of the coat.
A nearly horizontal crack (Crack III, pointed to by the black arrow in Figure 8a) in the coating was approximately 288 μm from the substrate surface, indicating the initiation and propagation of cracking at the TL/TIL interface. In this study, the thickness of the TGO layer increased to 4 µm, which induced tensile zone on the TC, the BC layer, and the TGO itself. Based on the results of finite element analysis in Ref. [39], the failure mechanism of plasma-sprayed TBC can be summarized as follows. First, the thickness of the TGO layer progressively increased with thermal cycles, and tensile stress concentration regions appeared at the peaks of TBC. Then, cracks occurred at the peak of the TGO/TL interface and propagated toward the valley region, motivated by microdefects and stress. From the magnified SEM image (Figure 8b), it can be seen that a crack was observed near the TGO. Based on the morphology, the initiation site is the peak of the TGO/TC interface. In addition, several vertical cracks were also found in the ceramic layer, motivated by microdefects and tensile stress during thermal cycles. As shown in Figure 8a, vertical cracks occurred near the surface of the TSL with relatively small dimensions, while larger t horizontal cracks occurred near areas of the TIL. The connection of these two types of cracks only occurred after the vertical cracks propagated through the entire TSL. Therefore, the failure caused by the connection of these two types of cracks does not seem to be easily formed; the propagation of the horizontal cracks would be the main cause of failure in this four-layer structure.
The elemental maps for the region in Figure 8a were acquired and presented in Figure 9. The aluminum and oxygen elements in TL were enriched in the TGO, while the nickel, chromium, and cobalt elements were mainly distributed in the residual matrix of TL. Compared to the as-sprayed state, the nickel content in the residual matrix of TL was close to that in the BL after thermal cycling.

3.6. Indentation

Nanoindentation tests were performed on the cross-sections in the samples of the as-sprayed state and after the thermal cycle test. The hardness and reduced modulus of the TSL are listed in Table 4. After the thermal cycle test, the hardness and reduced modulus values of TSL changed from 12,873.49 MPa to 13,077.77 MPa and from 161,183.61 MPa to 178,798.14 MPa, respectively. The increase in hardness and reduced modulus is attributed to the reduction in porosity and would result in a decrease in cracking resistance [36]. S. Nath et al. [42] have studied the effect of isothermal treatment on nanomechanical behavior of YSZ-based TBC, and the hardness of the TBC was found to increase with increased temperature of isothermal aging. In their study, the hardness of the as-sprayed state TBC increased to 13.9 GPa after isothermal aging at 1000 °C for 72 h, which is consistent with the result of this study (130,77.77 MPa).

4. Conclusions

Microstructure evolution and cracking behavior of a four-layer TBC during the thermal cycle test at 1100 °C under atmospheric conditions were studied. The results are listed as follows.
(1)
The TBC system is designed with a four-layer structure consisting of a TBC smooth layer, a TBC inner layer, a transition layer, and a bottom layer, with an average bond strength of 73.74 MPa. The TBC consists of tetragonal t and t′ phases, as well as monoclinic yttrium oxide.
(2)
After 500 thermal cycles, the m-ZrO2 phase was formed through the phase transformation of t′-ZrO2 to m-ZrO2 and c-ZrO2 during thermal cycle test. A large number of bulk TGO containing chromia, spinel, and yttrium aluminates were formed around pores within the transition layer. Furthermore, the increase rate of the TGO layer was relatively low, which may be attributed to the formation of bulk TGO around pores within the transition layer.
(3)
Large horizontal cracks are likely to form at the TSL/TIL and TIL/TL interfaces, while vertical cracks tend to occur near the surface of the TSL, and the propagation rate is relatively low. The propagation of horizontal cracks is the primary cause of failure in this four-layer structure.
(4)
After the thermal cycle test, the porosity of the TSL decreased significantly, from 7.17% to 0.76%, and the nanoindentation test revealed that there was a slight increase in hardness and reduced modulus.
In addition to thermal cycling performance, corrosion resistance is another very important performance indicator. The corrosion resistance of TBC will be investigated in subsequent experiments.

Author Contributions

Formal analysis, X.W. and Y.C.; Investigation, X.W. and Y.C.; Methodology, Y.Z. (Yang Zhou) and J.W.; Resources, Y.Z. (Yang Zhou); Supervision, J.W.; Validation, Y.Z. (Yuzhu Zhao); Writing—original draft, X.W.; Writing—review and editing, X.W., Y.C., Y.Z. (Yang Zhou), Y.Z. (Yuzhu Zhao) and J.W. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Zhejiang Provincial Postdoctoral Science Foundation (299342) and the Young Elite Scientists Sponsorship Program by CSEE (CSEE-YESS-2023003).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data are contained within the article.

Conflicts of Interest

Authors Xuyang Wang and Yuzhu Zhao were employed by the company Huadian Electric Power Research Institute Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Abbreviations

The following abbreviations are used in this manuscript:
BCBond coat
TGOThermally grown oxide
TCTop ceramic coat
CTECoefficient of thermal expansion
APSAtmospheric Plasma Spraying
EB-PVDElectron Beam Physical Vapor Deposition
CVDChemical Vapor Deposition
BLBottom layer
TLTransition layer
TILTBC inner layer
TSLTBC smooth layer

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Coatings 15 00307 g001
Figure 1. (a) Schematic diagram of the thermal cycle test setup; (b) schematic diagram of the sample temperature under a single thermal cycle.
Figure 1. (a) Schematic diagram of the thermal cycle test setup; (b) schematic diagram of the sample temperature under a single thermal cycle.
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Figure 2. Schematic diagram of the bond strength test.
Figure 2. Schematic diagram of the bond strength test.
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Figure 3. (a) XRD pattern of the as-sprayed coating; (b) the high-angle region of the diffraction pattern of the as-sprayed coating.
Figure 3. (a) XRD pattern of the as-sprayed coating; (b) the high-angle region of the diffraction pattern of the as-sprayed coating.
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Figure 4. (a) Cross-sectional SEM image of the TBC; (b) magnified SEM image of the TBC inner layer.
Figure 4. (a) Cross-sectional SEM image of the TBC; (b) magnified SEM image of the TBC inner layer.
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Figure 5. SEM-BSE image of the TL in the as-sprayed sample.
Figure 5. SEM-BSE image of the TL in the as-sprayed sample.
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Figure 6. Elemental maps of the region shown in Figure 4a mold by EDS.
Figure 6. Elemental maps of the region shown in Figure 4a mold by EDS.
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Figure 7. XRD pattern of the sample after the thermal cycle test.
Figure 7. XRD pattern of the sample after the thermal cycle test.
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Figure 8. (a) Cross-sectional SEM image of the TBC; (b) the magnified SEM image of the TL.
Figure 8. (a) Cross-sectional SEM image of the TBC; (b) the magnified SEM image of the TL.
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Figure 9. Elemental maps of the region shown in Figure 8a mold by EDS.
Figure 9. Elemental maps of the region shown in Figure 8a mold by EDS.
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Table 1. Main compositions of the substrate in the present study (wt. %).
Table 1. Main compositions of the substrate in the present study (wt. %).
AlloyCrCoAlTiTaWMoCNi
Substrate14.209.483.074.792.634.071.480.094balance
Table 2. Results of the bond strength.
Table 2. Results of the bond strength.
SampleLoad (N)Diameter (mm)Bond Strength (MPa)
138,588.3225.3076.7
234,629.4124.9770.8
Blank42,840.82-84.9
Table 3. The elemental composition of the dark contrast regions (at.%).
Table 3. The elemental composition of the dark contrast regions (at.%).
SiteNiAlCrYCoO
A0.2037.2---62.6
B10.9822.094.451.170.2161.10
C0.4425.110.7811.55-62.12
D49.968.0224.29-17.73
Table 4. Results of the nano-indentation tests.
Table 4. Results of the nano-indentation tests.
StateHardness (MPa)Reduced Mod. (MPa)
As-sprayed12,873.49161,183.61
Thermal cycle13,077.77178,798.14
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MDPI and ACS Style

Wang, X.; Cui, Y.; Zhou, Y.; Zhao, Y.; Wang, J. Microstructure and Cracking Behavior of a Four-Layer Thermal Barrier Coating After Thermal Cycle Test. Coatings 2025, 15, 307. https://doi.org/10.3390/coatings15030307

AMA Style

Wang X, Cui Y, Zhou Y, Zhao Y, Wang J. Microstructure and Cracking Behavior of a Four-Layer Thermal Barrier Coating After Thermal Cycle Test. Coatings. 2025; 15(3):307. https://doi.org/10.3390/coatings15030307

Chicago/Turabian Style

Wang, Xuyang, Yanna Cui, Yang Zhou, Yuzhu Zhao, and Jun Wang. 2025. "Microstructure and Cracking Behavior of a Four-Layer Thermal Barrier Coating After Thermal Cycle Test" Coatings 15, no. 3: 307. https://doi.org/10.3390/coatings15030307

APA Style

Wang, X., Cui, Y., Zhou, Y., Zhao, Y., & Wang, J. (2025). Microstructure and Cracking Behavior of a Four-Layer Thermal Barrier Coating After Thermal Cycle Test. Coatings, 15(3), 307. https://doi.org/10.3390/coatings15030307

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