Corrosion of RE2Si2O7 (RE=Y,Yb, and Lu) environmental barrier coating materials by molten calcium-magnesium-alumino-silicate glass at high temperatures

With the increased demand for high operating temperature of gas turbine engines, corrosion by molten calcium-magnesium-alumino-silicate (CMAS) exhibits a significant challenge to the development of durable environmental barrier coatings (EBCs). EBC candidates, γ-Y₂Si₂O₇, β-Yb₂Si₂O₇, and β-Lu₂Si₂O₇ were explored on their corrosion resistance to CMAS melts at 1300 °C and 1500 °C for 50 h. Interaction and degradation mechanisms were investigated and the corrosion behaviors showed different trends at high temperatures. At 1300 °C, RE₂Si₂O₇ dissolves into CMAS melts and apatite phases reprecipitate forming a thick recession layer. However, when the temperature increases to 1500 °C, CMAS melts vigorously penetrate through the grain boundary of RE₂Si₂O₇ and ‘blister’ cracks form throughout the samples. The reduced grain boundary stability at 1500 °C promotes the penetration of CMAS melts in RE₂Si₂O₇. Grain boundary engineering is critically demanded to optimize CMAS corrosion at high temperatures.     

High temperature performances of tri-layer environmental barrier coating with Si bond layer modified by Yb2O3

Environmental barrier coatings (EBCs) have been expected to be applied on the surface of ceramic matrix composites (CMCs). However, the oxidation and propagation cracking of the silicon bond layer are the most direct causes to induce the failure of EBCs under high temperature service environment. The modification of silicon bond layer has become an important method to prolong the service life of EBCs. In this work, the Yb₂O₃ have been introduced to the silicon bond layer, and three kinds of tri-layer Yb₂SiO₅/Yb₂Si₂O₇/(Si-xYb₂O₃) EBCs with modified Si bond layer by different contents of Yb₂O₃ (x = 0, 10 vol%, 15 vol%) were prepared by vacuum plasma spray technique. The thermal shock performance and long-term oxidation resistance of the EBCs at 1350 °C were investigated. The results showed that the addition of appropriate amount of Yb₂O₃ (10 vol%) can improve the structural stability and reduce the cracks of the mixed thermal growth oxide (mTGO) layer by forming the oxidation product of Yb₂Si₂O₇ during long-term oxidation. The excessive addition of Yb₂O₃ increased the stress during thermal shock as well as accelerated the oxygen diffusion during long-term oxidation, leading to the failure of EBCs. Moreover, the distribution uniformity of Yb₂O₃ deserves further consideration and improvement.     

High-entropy rare-earth disilicate (Lu0.2Yb0.2Er0.2Tm0.2Sc0.2)2Si2O7: A potential environmental barrier coating material

A new high-entropy ceramic (Lu_0.2Yb_0.2Er_0.2Tm_0.2Sc_0.2)₂Si₂O₇ ((5RE_0.2)₂Si₂O₇) was proposed as a potential environmental barrier coating (EBC) material for ceramics matrix composites in this work. Experimental results showed that the (5RE_0.2)₂Si₂O₇ synthesized by solid-phase sintering was a monoclinic solid solution and had good phase stability proved by no obvious absorption/exothermic peak in the DSC curve from room temperature to 1400 °C. It performed a lower coefficient of thermal expansion (2.08 ×10^?6-4.03 ×10^?6 °C^?1) and thermal conductivity (1.76–2.99 W?m^?1?°C^?1) compared with the five single principal RE₂Si₂O₇. In water vapor corrosion tests, (5RE_0.2)₂Si₂O₇ also exhibited better water vapor corrosion resistance attributed to the multiple doping effects. The weight loss was only 3.1831 × 10^?5 g?cm^?2 after 200 h corrosion at 1500 °C, which was lower than that of each single principal RE₂Si₂O₇. Therefore, (5RE_0.2)₂Si₂O₇ could be regarded as a remarkable candidate for EBCs.     

Interaction of Yb2Si2O7 environmental barrier coating material with Calcium-Ferrum-Alumina-Silicate (CFAS) at high temperature

Experimental investigations of Yb₂Si₂O₇ pellet exposed to Calcium-Ferrum-Alumina-Silicate (CFAS) at 1400 °C in ambient air were carried out to reveal corrosion reaction between molten silicate deposit and Yb₂Si₂O₇. Phase transformation, microstructure evolution and reaction mechanism were evaluated. Results indicated that the corrosion process was accompanied by the infiltration of CFAS melt, the dissolution of Yb₂Si₂O₇ and the reprecipitation of Yb₂Si₂O₇ and Ca₂Yb₈(SiO₄)₆O₂ apatite as reaction product. The formation of apatite decreased the concentration of Ca²⁺ in the melt. After CFAS exposure at 1400 °C for 30 h, the thickness of the apatite layer stopped increasing due to insufficient Ca²⁺ content, and remained at about 115.4 μm. However, the infiltration depth of CFAS melt increased with the extending corrosion duration and increasing deposit content. And the infiltration rate was preliminarily found to first decrease and then increase with time. Most of the residual CFAS were crystallized into garnet (Ca₃Fe₂(SiO₄)₃ and Yb₃Fe₅O₁₂) and mayerite (Ca₁₂Al₁₄O₃₃), while a small volume of amorphous glass was dispersed among the garnet and mayerite grains.     

High-Temperature thermochemical interactions of molten silicates with Yb2Si2O7 and Y2Si2O7 environmental barrier coating materials

The thermochemical behavior of EBC candidate materials yttrium disilicate (Y₂Si₂O₇) and ytterbium disilicate (Yb₂Si₂O₇) was evaluated with three calcium-magnesium-aluminosilicate (CMAS) glasses possessing CaO:SiO₂ ratios relevant to gas turbine systems. Pellet mixtures of 50 mol% EBC powder to 50 mol% CMAS glass powder were heat treated at 1200°C, 1300°C, and 1400°C. The products of these interactions were evaluated using X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. Above glass melting temperatures, exposure of the disilicates primarily resulted in dissolution into the molten glass followed by precipitation of a Ca₂RE₈(SiO₄)₆O₂ (RE = Yb³⁺, Y³⁺) apatite-type silicate and/or rare earth disilicate. In glasses with high CaO concentrations, apatite readily forms while the disilicate material is consumed by the reaction. As CaO content decreases, the disilicate phase becomes the main reaction product. Overall, reactions with yttrium disilicate favored more apatite crystallization than ytterbium disilicate. The viability of using these disilicates in various operating environments is discussed.     

Interaction of Gd2Si2O7 with CMAS melts for environmental barrier coatings

Environmental barrier coatings (EBCs) prevent the oxidation of ceramic matrix composites (CMC), which are used as components in gas turbines. However, EBCs deteriorate more rapidly in real environments, molten silicate deposits accelerate the deterioration of EBCs. In this study, high-temperature behavior sintered Gd₂Si₂O₇ with calcia-magnesia-alumina-silica (CMAS) melt at 1400 °C for 0.5, 2, 12, 48, and 100 h was investigated. HT-XRD results showed that at 1300 °C, CMAS and Gd₂Si₂O₇ chemically reacted to form Ca₂Gd₈(SiO₄)₆O₂ (apatite). The reaction layer became thicker as the heat-treatment time increased, and the thickness of the reaction layer has increased following a parabolic curve. With the extension of the reaction time from 0.5 to 100 h, the thickness of the reaction layer increased from approximately 98 to 315 µm. It was confirmed that Ca₂Gd₈(SiO₄)₆O₂ grew vertically on the Gd₂Si₂O₇ surface. Vertical and horizontal cracks were found after reacting at 1400 °C for 100 h, but no interfacial delamination occurred in this study. In addition, the effects of CaO:SiO₂ molar ratios, monosilicates (RE₂SiO₅) and disilicates (RE₂Si₂O₇), heat-treatment time, and cation size were determined and compared with the results of previous studies (Gd₂SiO_5, Yb₂SiO_5, and Er₂Si₂O₇).     

Thermal shock resistance of tri‐layer Yb2SiO5/Yb2Si2O7/Si coating for SiC and SiC‐matrix composites

A new tri‐layer Yb₂SiO₅/Yb₂Si₂O₇/Si coating was fabricated on SiC, C/SiC, and SiC/SiC substrates, respectively, using atmospheric plasma spray (APS) technique. All coated samples were subjected to thermal shock test at 1350°C. The evolution of phase composition and microstructure and thermo‐mechanical properties of those samples before and after thermal shock test were characterized. Results showed that adhesion between all the 3 layers and substrates appeared good. After thermal shock tests, through microcracks which penetrated the Yb₂SiO₅ top layer were mostly halted at the Yb₂SiO₅‐Yb₂Si₂O₇ interface and no thermal growth oxide (TGO) was formed after 40‐50 quenching cycles, implying the excellent crack propagation resistance of the environmental barrier coating (EBC) system. Transmission electron microscopy analysis confirmed that twinnings and dislocations were the main mechanisms of plastic deformation of the Yb₂Si₂O₇ coating, which might have positive effects on crack propagation resistance. The thermal shock behaviors were clarified based on thermal stresses combined with thermal expansion behaviors and elastic modulus analysis. This study provides a strategy for designing EBC systems with excellent crack propagation resistance.     

Constrained sintering and thermal ageing behaviour of electrophoretically deposited Yb2Si2O7 environmental barrier coating

The oxidation of SiC and the formation of a thermally grown oxide layer (TGO) limit the lifetime of environmental barrier coatings. Thus, this paper focuses on the deposition of denser Yb₂Si₂O₇ coatings using electrophoretic deposition to reduce the TGO growth rate. The findings showed densification for Yb₂Si₂O₇ can be achieved with an optimized sintering profile (heating/cooling rate, temperature, and time). However, the addition of 1.5 wt% of Al₂O₃ to Yb₂Si₂O₇ promoted densification and lowered the required sintering temperature, 1380 °C using 2 °C/min heating/cooling rate for 10 h provided efficient coating density. Moreover, adding Al₂O₃ reduced the TGO growth rate by more than 70 % compared to the Al₂O₃-free coatings, without cracking in TGO after 150 h of thermal ageing at 1350 °C. Results within this study suggest electrophoretic deposition with Al₂O₃ addition produces promising Yb₂Si₂O₇ environmental barrier coatings on SiC substrate with low oxidation rates and increased lifetime.     

Phase and microstructure evolution in plasma sprayed Yb2Si2O7 coatings

Yb₂Si₂O₇ coatings were deposited on Si/SiC substrates by atmospheric plasma spray (APS). The different power and plasma chemistries used in this work produced mainly amorphous crack-free coatings with compositions shifted to lower SiO₂ content with higher power and H₂ flow. Differences in microstructure and thermomechanical properties (crystallization behavior, thermal expansion coefficient and thermal conductivity) of as-deposited and thermally treated coatings were directly related to the evolution from amorphous to crystalline phases. A Yb₂SiO₅ metastable phase was identified after thermal treatments at temperatures ～ 1000 °C that transformed to its stable isomorph at 1220 °C. This transformation, followed by the growth of the crystal cell volume, promoted the coating expansion and the “healing” of microcracks present in the amorphous as-sprayed coating.     

Role of phonons on phase stabilization of RE2Si2O7 over wide temperature range (RE = Yb,Gd)

Thermodynamic phase stabilities of α, β, γ and δ polymorphs of RE₂Si₂O₇ (RE = Yb, Gd), promising candidates for environmental barrier coating systems of gas turbine engines in next generations, were investigated using harmonic and quasi-harmonic lattice dynamics in conjunction with ab initio calculations. By quantifying their Gibbs free energies with dynamics of atoms taken into account, we showed the phase stability of β-Yb₂Si₂O₇ up to melting temperature under an ideal condition, and also under thermal stresses, ensuring the reliability of β-Yb₂Si₂O₇ in environmental barrier coating systems. It was also found that the difference of anharmonic phonons in these polymorphs, which was measured as mode Grüneisen parameters, significantly changed their phonon free energies and invoked the formation of δ-Gd₂Si₂O₇ at high temperature. These results enable a quantitative comprehension of the phase transformation of RE₂Si₂O₇ and future discussions of other factors which may affect the phase stability such as lattice defects.     

Si/(Yb1-xYx)2Si2O7/LaMgAl11O19热/环境障涂层的高温性能研究

采用等离子喷涂法在碳化硅纤维增强碳化硅陶瓷基复合材料(SiC_f/SiC-CMCs)表面制备了Si/(Yb_1-xY_x)₂Si₂O₇/LaMgAl₁₁O₁₉(x=0、0.5)热/环境障涂层(T/EBCs)体系。通过SEM、EDS和XRD等测试方法研究了不同组成的T/EBCs体系在1 300 ℃下的热循环性能和抗水氧腐蚀性能,进而探讨了热循环失效和水氧腐蚀失效机理。结果表明,在T/EBCs体系中,Si/Yb₂Si₂O₇/LMA涂层体系的热循环寿命为403次,抗水氧腐蚀性能为50 h,Si/YbYSi₂O₇/LMA体系的热循环寿命降低至277次,而水氧腐蚀性能提高至80 h。YbYSi₂O₇与LMA之间较大的热失配应力以及层间含Al化合物或固溶体的生成是Si/YbYSi₂O₇/LMA热循环寿命降低的主要原因;YbYSi₂O₇-EBCs层较少的杂质氧化物减少了与水反应生成挥发性物质的几率,提高了Si/YbYSi₂O₇/LMA的抗水氧腐蚀能力。     

Interfacial reactions between B2O3 and spark plasma sintered Yb2Si2O7

Reactions between boria (B₂O₃) and Yb₂Si₂O₇ were studied via a series of idealized interfacial “well” tests. Boria oxidizes out of SiC/SiC ceramic matrix composites (CMCs) where BN is used as a fiber/matrix interphase and boron-rich inclusions often serve as aids in the melt infiltration process. Borate phases are highly reactive and can react with the rare earth silicates currently being utilized as environmental barrier coatings (EBCs) for these CMC systems. Ytterbium disilicate substrates for these well tests are prepared via spark plasma sintering. The well is then drilled into the substrates and filled with a boria glass plug. Exposures in a stagnant-air box furnace show that the boria is reacting with the disilicate via a substitution reaction leaving YbBO₃ and amorphous silica glass as the product phases. This phase was characterized with scanning electron microscopy and elemental dispersive spectroscopy (SEM/EDS), micro-focus X-ray diffraction, and selected-area electron diffraction (SAED). Inductively coupled plasma optical emission spectroscopy (ICP-OES) was also used to analyze water-soluble glassy phases left on the surface of the substrates post-exposure, indicating that the boron content of the glass was decreasing with both increasing exposure times and temperatures. There are few data on the borate product phase properties, however the results of this study suggest that the boria formed via oxidation from the SiC/BN/SiC composites could be detrimental to the performance of Yb₂Si₂O₇ environmental barrier coatings via formation of the borate phase and silica.     

Thermophysical performances of (La1/6Nd1/6Yb1/6Y1/6Sm1/6Lu1/6)2Ce2O7 high-entropy ceramics for thermal barrier coating applications

In this study, a novel high-entropy oxide of (La_1/6Nd_1/6Yb_1/6Y_1/6Sm_1/6Lu_1/6)₂Ce₂O₇was prepared using a sol–gel and high-temperature sintering technology. Additionally, its lattice structure, micro-morphology, elemental composition, and thermophysical and mechanical properties were evaluated. The results revealed that the obtained oxide powder has a typical fluorite-type lattice with particle sizes in the range of～30–100 nm. The bulk sample has a dense microstructure and uniform elemental distribution. Owing to its low lattice order, the thermal expansion coefficient of (La_1/6Nd_1/6Yb_1/6Y_1/6Sm_1/6Lu_1/6)₂Ce₂O₇ is greater than that of Sm₂Ce₂O₇, which also exhibits excellent lattice stability up to 1200 °C. Further, owing to phonon scattering due to lattice distortion, oxygen vacancy, and cation substitution, the thermal conductivity of (La_1/6Nd_1/6Yb_1/6Y_1/6Sm_1/6Lu_1/6)₂Ce₂O₇ is lower than that of Sm₂Ce₂O₇, while its mechanical performance is inferior to that of 7YSZ.     

Variable thermochemical stability of RE2Si2O7 (RE = Sc,Nd, Er,Yb, or Lu) in high-temperature high-velocity steam

Five rare-earth (RE) disilicates (RE₂Si₂O₇, RE = Sc, Nd, Er, Yb, or Lu) were synthesized and exposed to high-velocity steam (up to 235 m/s) for 125 hours at 1400°C. Water vapor reaction products, mass loss, average reaction depths, and product phase microstructural evolution were analyzed for each material after exposure. Similar to steam testing results in the literature, RE₂Si₂O₇ (RE = Er, Yb, Lu) underwent silica depletion producing gaseous silicon hydroxide species, RE₂SiO₅, and RE₂O₃ product phases. Sc₂Si₂O₇ reacted with high-velocity steam to produce only a Sc₂O₃ product layer with no stable Sc₂SiO₅ phase detected by X-ray diffraction or microscopy techniques. Further, Nd₂Si₂O₇ rapidly reacted with steam to produce with no Nd₂SiO₅ or Nd₂O₃ reaction products. All RE₂Si₂O₇ that produced a silicate reaction product (RE = Nd, Er, Yb, Lu) showed densification of the product phase at steam velocities above 150 m/s that resulted in enhanced resistance. The results presented in this work demonstrate that rare-earth silicates show diverse steam reaction products, reaction product microstructures, and total reaction depths after high-temperature high-velocity steam exposure. Of the materials in this study, RE₂Si₂O₇ (RE = Yb, Lu) were most stable in high-temperature high-velocity steam, making them most desirable as environmental barrier coating candidates.     

Thermal shock resistance and bonding strength of tri-layer Yb2SiO5/mullite/Si coating on SiCf/SiC composites

A Yb₂SiO₅/mullite/Si tri-layer environmental-barrier-coating (EBC) were coated on SiC_f/SiC substrates via Air Plasma Spraying (APS). The thermal cycle tests (TCT) were conducted under thermal corrosive condition of vapor-oxygen (50 vol% H₂O and 50 vol% O₂) with thermal shock from 1200 °C to 200 °C. Microstructures, weight loss and bonding strength of the samples were systemically investigated after 101, 396, 606 and 700 TCT cycles respectively. The results show that the corner of the tri-layer coating peel off from the sample with weight loss of 1.3% after 700 TCT cycles. The bonding strength between substrate and tri-layer coatings gradually decreases to 6.79 MPa (approximately 55.2% of virgin specimens) after 700 cycles due to thermal shock induced cracks distributed horizontally within Si layers and between Si layer and outer layers.     

Failure mechanisms in model thermal and environmental barrier coating systems

The durability of environmental barrier coating (EBC) systems in gas turbine engine environments depends upon their temperature dependent rates of degradation by processes such as steam volatilization and bond coat oxidation. While addition of a thermal barrier coating (TBC) reduces the temperature within the EBC system, it introduces new failure mechanisms. Deposition of a segmented HfO₂ TBC with a reduced in-plane Young’s modulus is essential to avoid bifurcated TBC channel cracking into a Yb₂Si₂O₇ EBC, and delamination, as a result of an approximately 50% difference in coefficients of thermal expansion (CTE) of the coating layers. During prolonged high temperature steam cycling, a thin fluorite phase reaction layer is observed to develop at the HfO₂-YbDS interface consistent with recent thermochemical assessments. The CTE of the fluorite phase is shown to be substantially higher than that of either of the layers to which it is bonded, resulting in tunnel cracking of the fluorite, and eventual coating delamination of the TBC at either the fluorite-HfO₂ or YbDS-fluorite interfaces upon cooling. The study highlights the importance of matching the CTEs of the TBC and EBC layers during coating system design, and those of the reaction products that may form between them.     

Investigation on behavior and mechanism of enhanced water vapor corrosion resistance for (Lu0.25Yb0.25Er0.25Y0.25)2SiO5 environmental barrier coating

Rare-earth monosilicate (RE₂SiO₅) have been considered to be a promising material for the environmental barrier coating because of their superior thermal and mechanical properties. However, the water vapor corrosion resistance of single-component RE-silicate materials, such as Y₂SiO₅, should be further improved. The high-entropy design is one of the most suitable methods to enhance the corrosion resistance for single-component RE-silicate materials. In this work, the multicomponent RE-silicate ((Lu_0.25Yb_0.25Er_0.25Y_0.25)₂SiO₅, (4HES)) and single-component RE-silicate (Y₂SiO₅) coatings were investigated with regard to its water vapor corrosion behaviors at 1350 °C for 300 h. A thinner and denser corrosion layer was generated in the 4HES coating, indicating that the 4HES coating possessed better corrosion resistance than the Y₂SiO₅ coating. The improved corrosion resistance is attributed to the better hydrophobic property as well as the more stable crystal structure of the rare-earth oxide and 4HES phase which was resulted from the high-entropy design.     

Crack-healing behaviour of MoSi2 dispersed Yb2Si2O7 environmental barrier coatings

MoSi₂ doped Yb₂Si₂O₇ composites were designed to extend the lifetime of Yb₂Si₂O₇ environmental barrier coatings (EBCs) via self-healing cracks during high-temperature applications. Yb₂Si₂O₇–Yb₂SiO₅–MoSi₂ composites with different mass fractions were prepared by applying spark plasma sintering. X-ray diffraction results confirmed that the composites consisted of Yb₂Si₂O₇, Yb₂SiO₅, and MoSi₂. The thermal expansion coefficients (CTEs) of the composites increased with an increase in the MoSi₂ content. The average CTE of the 15 wt% MoSi₂ doped Yb₂Si₂O₇ composite was 5.24 × 10^?6 K^?1, indicating that it still meets the CTE requirement of EBC materials. After being pre-cracked by using the Vickers indentation technique, the samples were annealed for 0.5 h at 1100 or 1300 °C to evaluate the crack-healing ability. Microstructural studies showed that cracks in 15 wt% MoSi₂ doped Yb₂Si₂O₇ composites were fully healed during annealing at 1300 °C. Two mechanisms may be responsible for crack healing. First, the cracks were filled with SiO₂ glass formed by MoSi₂ oxidation. Second, the formed SiO₂ continued to react with Yb₂SiO₅ to form Yb₂Si₂O₇, which can cause cracks to heal owing to volumetric expansion. The Yb₂Si₂O₇ formation with smaller volume expansion is more beneficial.     

Composition effects on elastic,thermal and corrosion properties of multiple-RE silicate (Ho1/4Er1/4Yb1/4Lu1/4)2SiO5 as a promising thermal and environmental barrier coating material

(Ho_1/4Er_1/4Yb_1/4Lu_1/4)₂SiO₅ is synthesized and characterized for the application of a promising multifunctional thermal and environmental barrier coating (TEBC) material. X-ray diffraction and scanning electron microscopy analysis indicate that a X2-type multiple-RE silicate (4RE_1/4)₂SiO₅ is formed with homogeneous distribution of the four rare earth species. Dense bulk sample exhibits excellent phase stability up to 1400 °C. Key properties including Young’s modulus, thermal conductivity and thermal expansion coefficient show interesting composition effects. Specially, (Ho_1/4Er_1/4Yb_1/4Lu_1/4)₂SiO₅ demonstrates higher elastic stiffness, lower thermal conductivity, lower thermal expansion coefficient and good resistances to molten CMAS and water vapor corrosions. These results confirm the strategy of multiple-RE engineering that may provide optimal property of advanced TEBCs.     

Feasibility research of Yb3Al5O12 garnet as environmental barrier coating materials

In this work, Yb₃Al₅O₁₂ (YbAG) garnet, as a new material for environment barrier coating (EBC) application, was synthesized and prepared by atmospheric plasma spraying (APS). The phases and microstructures of the coatings were characterized by XRD, EDS and SEM, respectively. The thermal stability was measured by TG-DSC. The mechanical and thermal-physical properties, including Vickers hardness (H_v), fracture toughness (K_IC), Young's modulus (E), thermal conductivity (κ) and coefficient of thermal expansion (CTE) were also measured. The results showed that the as-sprayed coating was mainly composed of crystalline Yb₃Al₅O₁₂ and amorphous phase which crystallized at around 917 °C. Moreover, it has a hardness of 6.81 ± 0.23 GPa, fracture toughness of 1.61 ± 0.18 MPa m^1/2, as well as low thermal conductivity (0.82–1.37 W/m·K from RT-1000 °C) and an average coefficient of thermal expansion (CTE) (∼6.3 × 10⁻⁶ K⁻¹ from RT to 660 °C). In addition, the thermal shock and water-vapor corrosion behaviors of the Yb₃Al₅O₁₂-EBC systems on the SiC_f/SiC substrates were investigated and their failure mechanisms were analyzed in details. The Yb₃Al₅O₁₂ coating has an average thermal shock lifetime of 72 ± 10 cycles as well as an excellent resistance to steam. These combined properties indicated that the Yb₃Al₅O₁₂ coating might be a potential EBC material. Both the thermal shock failure and the steam recession of the Yb₃Al₅O₁₂-EBC systems are primarily associated with the CTE mismatch stress.