Abstract ：

本发明涉及热障涂层表面腐蚀与防护技术领域，特别是涉及一种抗CMAS浸润的仿生热障涂层及制备方法。该抗CMAS浸润的仿生热障涂层，从基体开始，由内向外，依次包括：金属粘结层、内陶瓷层和微纳结构外陶瓷层；所述微纳结构外陶瓷层为NdYbZr2O7。本发明采用悬浮液等离子喷涂技术在内陶瓷层表面制备微纳结构外陶瓷层。本发明选择新型NdYbZr2O7材料作为外陶瓷层材料，同时基于悬浮液等离子喷涂技术，从材料组分优化和结构调控两方面入手，实现主/被动结合的CMAS防护效果，提升涂层抗CMAS浸润和腐蚀性能。

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Abstract ：

Although rare earth zirconates (RE2Zr2O7) have garnered attention as viable candidates for thermal barrier coatings (TBCs), they suffer from low fracture toughness and accelerated calcium-magnesium-alumina-silicate (CMAS) melt corrosion at high service temperatures, which impedes their practical application. In this work, we developed a series of REAlO3/RE2Zr2O7 (RE = La, Nd, Sm, Eu, Gd, and Dy) composites with a eutectic composition that not only significantly enhanced the fracture toughness by more than 40% relative to that of RE2Zr2O7 but also exhibited improved resistance to CMAS corrosion. The increase in toughness arises from multiple mechanisms, such as ferroelastic toughening, fine-grain strengthening, and residual stress toughening, all of which trigger more crack defects and energy consumption. Additionally, the CMAS penetration depth of the REAlO3/RE2Zr2O7 composites is approximately 36% lower than that of RE2Zr2O7. Al-O constituents in composites can capture CaO, SiO2, and MgO in CMAS melts and increase their viscosity, resulting in enhanced CMAS corrosion resistance. The thermophysical properties of the REAlO3/RE2Zr2O7 composites were also investigated, and their coefficient of thermal expansion and thermal conductivity are comparable to those of 7-8 wt %Y2O3 partially stabilized ZrO2 (YSZ), indicating their potential as TBC materials.

Keyword ：

calcium-magnesium-alumina-silicate (CMAS) corrosion thermal property eutectic composition REAlO3/RE2Zr2O7 fracture toughness

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Abstract ：

With the increasing operating temperature of gas turbine engines, calcium-magnesium-aluminosilicate (CMAS) poses a serious threat on environmental barrier coatings (EBCs) applied on hot-sections of aero-engines. Here, we have synthesized a novel multicomponent disilicate-(Ho0.2Er0.2Tm0.2Yb0.2Lu0.2)(2)Si2O7 (brief to (5RE(0.2))(2)Si2O7), and comparatively studied its performance in the presence of synthesized CMAS and natural volcanic ash at 1400 degrees C. In comparison with Yb2Si2O7, (5RE(0.2))(2)Si2O7 has a shorter Si-O bond length and a larger RE-O bond length because of the larger average RE3+ radius. After CMAS corrosion, some apatite grains precipitate at the CMAS/(5RE(0.2))(2)Si2O7 interface to develop a loose reaction layer, exhibiting a higher corrosion resistance than Yb2Si2O7. Meanwhile, the consumption of CaO and release of SiO2 during the chemical reaction process increase the viscosity of CMAS to some extent and thus weaken its infiltration propensity. For the volcanic ash case, it directly infiltrates into the interior of (5RE(0.2))(2)Si2O7 along grain boundaries without any reaction due to the relatively low CaO content, exhibiting a more serious attacking behavior. In addition, (5RE(0.2))(2)Si2O7 effectively increases the contact angle of molten volcanic ash due to its lower surface energy. These finds here provide a better understanding for the design and application of next-generation EBC material.

Keyword ：

Volcanic ash Environmental barrier coatings (EBCs) Multicomponent disilicate CMAS

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Abstract ：

Molten calcium-magnesium-aluminosilicate (CMAS) poses a considerable threat to the environmental barrier coatings (EBCs) service life. Here, we have prepared ytterbium monosilicate (YbMS) and ytterbium disilicate (YbDS) coatings using air plasma spraying (APS), and comprehensively investigated their high -temperature response to two CMAS relevant to real sediments within gas turbine and Beijing sand -dust, which are defined as CaO-rich CMAS and CaO-lean CMAS respectively. In the CaO-rich CMAS case, either YbMS or YbDS coating exhibits a vigorous reaction and rapid precipitation of apatite phase, constructing a dense reaction layer and inhibiting the molten CMAS infiltration. Note that the YbMS coating always possesses a smaller infiltration depth than YbDS coating because of the synergistic effect of its higher reactivity and more stable crystal structure. In comparison, the molten CaO-lean CMAS infiltrates along the grain boundaries of both coatings without any barrier, only some re -precipitated YbDS grains exist at the CMAS/coating interface. This phenomenon is closely related to the relatively high Yb3+ solubility due to its lower CaO content relative to the CaO-rich CMAS. These finds in this work are expected to provide a better understanding for the design of next -generation EBCs material and proposal of effective methods to mitigate the molten CMAS attack.

Keyword ：

Ytterbium monosilicate Ytterbium disilicate Calcium-magnesium-aluminosilicate (CMAS) Environmental barrier coatings (EBCs)

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Abstract ：

Thermal barrier coatings (TBCs) are widely used in the hot-section components of gas-turbine engines to allow operation at higher temperatures (> 1 200 degrees C), which has created some new issues. One issue is the spallation and premature failure of TBCs caused by calcium-magnesium-alumino-silicate (CMAS) deposits, which arise from entry of siliceous debris such as fly ash, sand, dust, and volcanic ash into engines. Since 1953, over 130 jet aircraft have encountered volcanic ash clouds, with varying degrees of damage and endangering the lives of many passengers. The 2010 eruption of Eyjafjallajokull volcano in Iceland led to the most severe air-traffic disruption since World War II. The operational response produced economic losses approaching 1.7 billion. When these debris enter the hot-section airfoil, they melt and are accelerated from low speed (similar to 15 m / s) to near supersonic speed (similar to 300 m / s), impacting and adhering to the TBC surface. Even with only a few molten silicate ash droplets adhering to the surface of hot-section airfoils, an initial deposit layer can form and large melt pockets (several cubic centimeters in volume) can accumulate. Such deposits can 1) block cooling holes and air flow paths, and 2) react with the top coating of hot-section airfoils. Furthermore, adhering droplets infiltrate the interior of TBCs under capillary forces. Due to the thermal gradient and thermal cycling, the infiltrated CMAS solidifies and fills in the microcracks, pores, and grain boundaries, resulting in loss of strain tolerance and increased coating stiffness. For traditional 7-8 wt.% yttria-stabilized zirconia (YSZ) material, chemical reaction with CMAS destroys the phase and structure stability. YSZ grains dissolve and Y-depleted ZrO2 grains precipitate due to the relatively low solubility of Zr4+ compared with Y3+ in melted CMAS. Upon cooling, the newly formed grains transform from tetragonal (t) to monoclinic (m) phases, accompanied by a 3%-4% volume expansion. As turbine inlet temperatures improve and industry production grows, TBCs are suffering from severe CMAS corrosion. This issue limits further application and development of TBCs; enhancing anti-corrosion performance of TBCs has become a concern. Herein, we compare the room-temperature and high-temperature properties of different CMAS and study the failure mechanism of TBCs exposed to CMAS. We also determine the most effective CMAS protection method. The results show that the chemical compositions, especially the Ca:Si ratio, of CMAS such as volcanic ash, dust and sand are different, further affecting their high-temperature viscosities and melting behaviors. With infiltration of molten CMAS toward the coating interior, chemical reaction occurs between them, resulting in instability of the coating microstructure and properties, and failure. Significant methods including inert-layer, rare-earth doping and novel materials have been proposed to improve the CMAS corrosion resistance of TBCs. The research and future development directions of CMAS corrosion and protection are proposed, providing a reference for design of novel TBCs.

Keyword ：

advanced aero-engines thermal barrier coatings(TBCs) corrosion protection calcium-magnesium-alumino-silicate(CMAS)

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Abstract ：

This chapter discusses the basic evaluation technologies for the investigation of the physical, thermal, and mechanical properties of the thermal barrier coatings (TBCs), as well as the experimental methods to evaluate thermal stability and chemical stability performance. All the technologies involved in this chapter were already successfully conducted to analyze the properties and performance of the TBCs. Specifically, the techniques to evaluate the density, porosity, phase, and lattice structures are summarized to evaluate the physical properties in Section 9.1. For the mechanical properties, we will focus on the hardness, elastic properties, bond strength, fracture toughness, erosion, and residual stress in Section 9.2. The approaches to detect the melting point, specific heat capacity, thermal conductivity, and coefficient of thermal expansion of TBCs are combined to analyze typical thermal properties in Section 9.3. To simulate the operational environment, the thermal cycling, thermal gradient fatigue test, oxidation test, corrosion evaluation techniques for hot-salt corrosive substance, the calcium–magnesium–aluminum–silicon oxide (CMAS), and water vapor are used to systematically investigate the operational performance of the TBCs in Sections 9.4 and 9.5. The properties and performance evaluation technologies described in this chapter provide a fundamental view for the research and development of novel TBCs materials. © 2023 Elsevier Ltd. All rights reserved.

Keyword ：

Mechanical properties Thermal stability Thermal properties Chemical stability Thermal barrier coatings (TBCs)

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Abstract ：

本发明涉及热障涂层表面腐蚀与防护技术领域，具体为一种抗熔融CMAS附着和腐蚀的热障防护层的制备方法，由下至上包括高温合金基材、YSZ层和NdYbZr2O7防护层；所述YSZ层为氧化钇稳定氧化锆；所述NdYbZr2O7防护层表面具有微米柱结构。本发明在YSZ层表面制备一层NdYbZr2O7防护层，具有优异的抗高温烧结和抗CMAS腐蚀性能，同时具备相对较低的表面能，有利于提高防护层抗熔融CMAS粘附和浸润性；利用表面规则排布的微米级凸台阵列和随机分布的大量纳米颗粒结构，能够进一步降低熔融CMAS在涂层表面的粘附和浸润倾向性，提升涂层的抗CMAS腐蚀性能。

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Abstract ：

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.

Keyword ：

Numerical simulation Thermal shock resistance Thermal barrier coatings CMAS corrosion resistance

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Abstract ：

热障涂层(TBCs)广泛应用于先进航空发动机热端部件,可以有效提高发动机的工作效率和服役温度.随着发动机涡轮前进口温度不断提高以及工业生产和人类活动愈加频繁,TBCs面临严峻的CMAS腐蚀问题.目前CMAS腐蚀已经成为制约TBCs应用和发展的关键因素,如何提高TBCs的CMAS防护能力是TBCs领域的研究热点和难点.针对此问题,对不同类型CMAS的室温和高温特性进行总结,深入分析CMAS作用下TBCs的失效机制,总结TBCs的CMAS防护方法,综述TBCs的CMAS腐蚀与防护研究进展.结果表明,不同CMAS(如火山灰、沙石和灰尘等)的化学成分(质量分数)差异明显,影响了其高温黏度和熔化行为;高温下熔融CMAS渗入到涂层内部并与之发生化学反应,破坏了涂层的结构和性能稳定性,造成涂层失效;提出了增加惰性防护层、YSZ材料掺杂改性和研发新材料等方法,以提高TBCs的CMAS防护能力.最后对未来的CMAS防护新方法进行展望,对超高温长寿命TBCs的研制提供理论支撑.

Keyword ：

热障涂层 先进航空发动机 CMAS 腐蚀防护

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Rare-earth zirconates (RE2Zr2O7) are potential thermal barrier coatings (TBCs) candidates exhibiting excellent thermal insulation property to protect underlying superalloy substrate. These coating materials, however, are subjected to degradation caused by molten silicon-containing sand dust and volcanic ash whose main compo-sitions are CaO-MgO-AlO1.5-SiO2 (brief to CMAS) at higher operating temperatures (> 1200 degrees C). Here, we have studied the thermochemical interactions between three RE2Zr2O7 (Sm2Zr2O7, Gd2Zr2O7 and Yb2Zr2O7) and CMAS with three different compositions (referred to as CMAS-1, CMAS-2 and CMAS-3, respectively) at 1300 degrees C/ 30 min. Both the diversities of the REO1.5 identity and CMAS composition result in the precipitation of apatite with varying stoichiometry. For an equivalent CMAS case, there is a linear correlation between the apatite content and the RE cation radius. In CMAS-1, the Ca:RE ratio of apatite observed in the Sm2Zr2O7 case is-0.31, larger than that of Gd2Zr2O7 (-0.30) and Yb2Zr2O7 (-0.20). Additionally, the RE3+ solubility in equilibrium with apatite decreases with the increased CaO content from CMAS-3 to CMAS-1 for a given RE2Zr2O7 material, facilitating the apatite precipitation within a short time. For example, in Sm2Zr2O7 case the Sm3+ solubility decrease from-3.18 at % to-0.70 at % as the CaO content increases from 19 mol % ( in CMAS-3) to 33 mol % ( in CMAS-1). Also, the composition of residual CMAS melt changes as the interaction proceed, which can impact its flow property and infiltration propensity. These finds may advance the design of current and next-generation TBCs material and development of effective strategies to mitigate the CMAS-induced coating failure.

Keyword ：

Thermal barrier coatings (TBCs) CMAS Interaction

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