航空发动机热障涂层的CMAS腐蚀行为与防护方法

热障涂层(thermal barrier coatings,TBCs)是航空发动机涡轮叶片的关键核心技术之一,可显著提高发动机工作温度,提升发动机推力和工作效率;但另一方面,更高的发动机工作温度使得叶片及其表面TBCs遭受严重的环境沉积物(主要成分为CaO、MgO、Al2O3和SiO2,简称CMAS)腐蚀,造成过早失效.CMAS腐蚀已成为限制TBCs工作温度和服役寿命的难题,抗腐蚀防护是目前TBCs领域研究的重点.本文首先综述了学者们对TBCs CMAS腐蚀问题的认识历程以及CMAS本身特性,再简述了TBCs的CMAS腐蚀机理,重点从TBCs的表面防护层设计、涂层成分改性、新型抗腐蚀涂层材料开发以及涂层结构设计等方面阐述了国际上目前TBCs的抗CMAS腐蚀防护方法,最后对TBCs的超高温环境应用及腐蚀防护发展方向进行了展望.     

熔融硅酸盐环境沉积物(CMAS)在不同表面粗糙度的热障涂层表面润湿行为EI北大核心CSCD

随航空发动机涡轮端进口温度提高,硅酸盐环境沉积物(CMAS)成为高温部件热障涂层(TBCs)失效的重要威胁。研究热障涂层与CMAS的作用关系,可为提高热障涂层的服役寿命提供基础。目前表面粗糙度(Ra)对高温熔体润湿性能的影响并未形成明确统一的定论,针对TBCs/CMAS体系润湿性的研究较少。采用座滴法研究1300℃条件下氧化钇部分稳定氧化锆(YSZ)涂层Ra对熔融CMAS润湿行为和渗透行为的影响。结果表明,在研究的涂层表面粗糙度的范围内,随着Ra的减小,熔融CMAS的润湿半径减小,接触角增大,渗透深度减小。由此推断粗糙表面有利于涂层抗润湿性能的增强。粗糙涂层表面为熔融CMAS铺展提供驱动力,促进三相线的移动;同时,粗糙涂层表面具有更大的实际接触面积以及更多的渗透方向,为CMAS渗透提供了有利条件。研究结果可为进一步开发表面不浸润的抗CMAS腐蚀热障涂层提供理论和实践依据。     

服役环境对涡轮导向叶片热障涂层失效模式的影响

目的 基于服役环境下热障涂层失效行为的复杂性,分析服役环境对涡轮导向叶片热障涂层的影响,并总结涡轮导向叶片热障涂层的失效模式。方法 针对服役环境下某型民用航空发动机涡轮导向叶片,使用UG软件建模,并且采用FLUENT软件对其进行三维共轭传热计算,结合热障涂层宏微观形貌、钙镁铝硅酸盐（CMAS）侵蚀行为、热生长氧化物（TGO）的生长情况,以及孔隙率和硬度的变化,通过引入涂层损伤系数,建立一种新的热障涂层区域失效评估模式,综合分析服役环境对涡轮导向叶片热障涂层区域化失效模式的影响。结果 在经历了8500h服役后,涡轮导向叶片表面热障涂层的失效模式因服役环境的局部差异而不同。叶片前缘区域最高温度达到1 501.69 K,发生了严重的低熔点氧化物侵蚀,导致陶瓷层的孔隙率降至11.909%,TGO等效厚度生长至1.870μm。后缘区域的最低温度为980.46 K,未见CMAS侵蚀,陶瓷层的孔隙率降至13.701%,TGO等效厚度生长至2.676μm。叶盆、叶背表面平均温度分别为1363.47K和1 264.14 K,发生了轻度低熔点氧化物侵蚀,陶瓷层的孔隙率分别降至12.176%和13.371%...     

热障涂层抗腐蚀研究进展

腐蚀是燃气轮机涡轮叶片Y2O3稳定ZrO2(YSZ)热障涂层失效的主要原因.本文系统总结了YSZ热障涂层服役过程中面临的腐蚀环境:高温相变、烧结与氧化腐蚀,Na2SO4和V2Os熔盐腐蚀,以及熔融钙镁铝硅酸盐玻璃(CMAS)腐蚀.分析了YSZ热障涂层腐蚀机理,讨论了提高热障涂层抗腐蚀性能的理论和方法,指出了热障涂层抗腐蚀研究发展方向.     

防CMAS腐蚀热障涂层开裂的研究现状

针对热障涂层在服役过程中受CMAS(Ca O-Mg O-Al2O3-Si O2)腐蚀而造成的表层剥落及层间易开裂问题,探讨总结了CMAS对于热障涂层的腐蚀机理,指出目前所用方法存在的不足,因此急需研究抗CMAS腐蚀的新材料系统和相关工艺。开裂失效是热障涂层主要的失效形式,通过降低氧化层的氧化速度和增加陶瓷层的韧性,能有效延长涂层的使用寿命。基于对涂层结构复杂性的分析,可知涂层需从宏观、细观、微观三个角度进行表述,因此合理运用跨尺度理论对于分析涂层结构等问题有着较为重要的意义。为此提出开发防CMAS渗入的细观增韧的热障涂层,并进一步从跨尺度角度进行开裂分析。研究结果对于丰富涂层增韧途径、增强抗腐蚀性能,保障热障涂层乃至航空发动机的安全平稳运行具有重要的理论意义和工程应用价值。     

航空发动机涡轮叶片热障涂层失效分析研究

采用扫描电镜及能谱对航空发动机涡轮叶片热障涂层进行失效分析,将叶片划分为9个区域,发现其前缘区域由于涂层的使用温度高、粘结层氧化、尖晶石等大量生长,导致在TGO/陶瓷层界面处产生大量的生长应力,呈TGO/Top coat界面分层失效。后缘区域呈粘结层/基体分层分裂失效,同时所有区域都有CMAS腐蚀。CMAS附着在涂层表面,沿着纵向裂纹等缺陷渗透到涂层内部,引发涂层产生横向分层,并导致涂层腐蚀剥落。     

CMAS、CMAS+NaVO3、CMAS+海盐作用下热障涂层的腐蚀行为与机理

环境沉积物(CaO-MgO-Al₂O₃-SiO₂,CMAS)的高温腐蚀已成为航空发动机涡轮叶片热障涂层过早失效的重要原因之一。然而涡轮叶片工作环境复杂,熔盐、海盐常与CMAS耦合,一起对热障涂层造成多元复杂腐蚀,但目前关于CMAS与盐类的多元耦合腐蚀行为鲜有报道。针对Y₂O₃部分稳定ZrO₂(YSZ)热障涂层在CMAS、CMAS+NaVO₃、CMAS+海盐作用下的腐蚀行为进行对比研究。通过XRD、SEM等方法对不同条件下腐蚀后的涂层进行表征,并分析热处理温度、腐蚀物种类对腐蚀行为的影响。结果表明：与CMAS相比,CMAS+NaVO₃、CMAS+海盐会在更低的温度下损伤涂层(1 200℃)。当三种腐蚀物均能完全熔化时(1 250℃),CMAS+NaVO₃、CMAS+海盐熔体则由于更大的流动性而大量渗入,腐蚀内部涂层。其中,CMAS+海盐熔体在涂层内的渗透性最强,1 250℃热处理4 h后,渗透...     

航空发动机涡轮叶片热障涂层研究现状

热障涂层是一种可以有效保障航空发动机涡轮叶片正常工作，同时显著提高其工作效率和服役时间的表面防护技术。热障涂层的性能在很大程度上影响叶片的承温和抗腐蚀能力，进而间接影响航空发动机的服役性能。涂层性能主要受其结构和材料2个方面的影响。介绍了涂层结构的优缺点和研究进展，当前常见的结构形式有双层结构、多层结构和梯度结构；介绍了粘结层材料的研究进展；对陶瓷层材料的研究进展进行了详述，如YSZ的掺杂改性、A₂B₂O₇型化合物、钙钛矿结构材料以及近年来兴起的几种高熵陶瓷材料，其中高熵陶瓷材料包括：高熵稀土钽酸盐、铝酸盐、锆/铪酸盐、磷酸盐、硅酸盐以及高熵稀土氧化物，分别从热导率、热膨胀系数、断裂韧性、热循环寿命和抗腐蚀能力等方面对其进行介绍；概述了热障涂层常见的几种失效形式如：TGO失效、CMAS腐蚀以及高温烧结，并且对其发生机理进行简要的介绍；展望了热障涂层未来的发展趋势和方向。     

CMAS对热障涂层界面裂纹和残余应力的影响

随着航空发动机涡轮叶片工作温度的提升,使得一种主要由CaO,MgO,Al₂O₃和SiO₂组成的玻璃态物质(CMAS)对热障涂层的危害越来越严重,从而对热障涂层的性能和耐久性有了更高的要求。本文以电子束物理气相沉积热障涂层为研究对象,利用有限元方法研究了CMAS的渗入对界面裂纹扩展及CMAS对陶瓷层(TC)内部残余应力的影响规律。采用波长固定、振幅变化的正弦曲线表示不同粗糙度的涂层界面,同时考虑了CMAS的弹性模量变化的影响及不同界面形貌与CMAS之间的相互作用。结果表明：CMAS弹性模量的增加对界面裂纹具有抑制作用,并且TGO幅值和厚度越小,抑制作用越明显。CMAS弹性模量对TC层最大残余应力S₂₂的影响存在临界点,在临界点之前,CMAS弹性模量的变化对TC层最大残余应力的影响较大,随着CMAS弹性模量的增加,TC层最大残余应力大幅度减小；在临界点之后,TC层最大残余应力基本不受CMAS弹性模量变化的影响。这些结果对电子束物理气相沉积喷涂的热障涂层失效机理的研究具有重要意义,可以为热障涂层界面的优化提供指导。     

高温燃气下CMAS混合盐覆盖对YSZ热障涂层性能的影响

分别采用大气等离子喷涂(APS)和等离子喷涂-物理气相沉积(PS-PVD)两种工艺方法制备YSZ(Y_2O_3稳定ZrO_2)热障涂层,同时在YSZ涂层表面沉积CMAS(CaO-MgO-Al_2O_3-SiO_2)混合盐,研究高温燃气持续加热下两种YSZ涂层的抗CMAS腐蚀行为。采用SEM、EDS、XRD等检测手段表征热障涂层腐蚀前后的微观结构、成分及物相变化。结果表明:APS-YSZ涂层在高温下经CMAS渗透后从基体整块剥落,涂层快速失效,而PS-PVD-YSZ涂层经高温燃气加热后同样被CMAS渗入,但并未发生明显涂层剥落,抗CMAS腐蚀剥落性能明显优于APS-YSZ涂层。分析表明CMAS混合盐对YSZ层的失效作用主要表现为热机械作用,其中APS-YSZ涂层应变容限较小,在涂层冷却过程中出现整块剥离现象,而PS-PVD-YSZ涂层应变容限较大,抗热震性好,涂层未出现整块剥离现象。     

Air-plasma-sprayed thermal barrier coatings that are resistant to high-temperature attack by glassy deposits

Thermal barrier coatings (TBCs) used in gas-turbine engines afford higher operating temperatures, resulting in enhanced efficiencies and performance. However, at these high operating temperatures, environmentally ingested airborne sand/ash particles melt on the hot TBC surfaces and form calcium–magnesium–aluminosilicate (CMAS) glass deposits. The molten CMAS glass penetrates the TBCs, leading to loss of strain tolerance and TBC failure. Here we demonstrate the use of the commercial manufacturing method of air-plasma-spray (APS) to fabricate CMAS-resistant yttria-stabilized zirconia (YSZ)-based TBCs containing Al and Ti in solid solution. Results from thermal stability studies of these new TBCs and CMAS/TBC interaction experiments are presented, together with a discussion of the CMAS mitigation mechanisms. The ubiquity of airborne sand/ash particles and the ever-increasing demand for higher operating temperatures in future high efficiency/performance gas-turbine engines will necessitate CMAS resistance in all hot-section components of those engines. In this context the versatility, ease of processing, and low cost offered by the APS method has broad implications for the design and fabrication of next-generation CMAS-resistant TBCs for future engines.     

CMAS-Resistant Plasma Sprayed Thermal Barrier Coatings Based on Y2O3-Stabilized ZrO2 with Al3+ and Ti4+ Solute Additions

The higher operating temperatures in gas-turbine engines made possible by thermal barrier coatings (TBCs) are engendering a new problem: environmentally ingested airborne silicate particles (sand, ash) melt on the hot TBC surfaces and form calcium-magnesium-alumino-silicate (CMAS) glass deposits. The molten CMAS glass degrades the TBCs, leading to their premature failure. Here, we demonstrate the use of a commercially manufactured feedstock powder, in conjunction with air plasma spray process, to deposit CMAS-resistant yttria-stabilized zirconia-based TBCs containing Al³⁺ and Ti⁴⁺ in solid solution. Results from the characterization of these new TBCs and CMAS/TBCs interaction experiments are presented. The CMAS mitigation mechanisms in these new TBCs involve the crystallization of the anorthite phase. Raman microscopy is used to generate large area maps of the anorthite phase in the CMAS-interacted TBCs demonstrating the potential usefulness of this method for studying CMAS/TBCs interactions. The ubiquity of airborne sand/ash particles and the ever-increasing demand for higher operating temperatures in future high efficiency gas-turbine engines will necessitate CMAS resistance in all hot-section components of those engines. In this context, the versatility, ease of processing, and low cost offered by the process demonstrated here could benefit the development of these new CMAS-resistant TBCs.     

Novel thermal barrier coatings that are resistant to high-temperature attack by glassy deposits

Airborne sand particles that deposit on thermal barrier coatings (TBCs) in gas-turbine engines melt and form calcium–magnesium–aluminosilicate (CMAS) glass, which attacks the TBCs. A new approach for mitigating CMAS attack on TBCs is presented, where up to 20 mol.% Al₂O₃ and 5 mol.% TiO₂ in the form of a solid solution is incorporated into Y₂O₃-stabilized ZrO₂ (YSZ) TBCs. The fabrication of such TBCs with engineered chemistries is made possible by the solution-precursor plasma spray (SPPS) process, which is uniquely suited for depositing coatings of metastable ceramics with extended solid-solubilities. Here, the TBC serves as a reservoir of Al and Ti solutes, which are incorporated into the molten CMAS glass that is in contact with the TBC. This results in the crystallization of the CMAS glass and the attendant arrest of the penetrating CMAS front. This approach could also be used to mitigate attack by other types of foreign deposits (salt, ash, and contaminants) on TBCs.     

CMAS corrosion of EB PVD TBCs: Identifying the minimum level to initiate damage

Over the last decade a significant amount of research has been conducted into the durability of thermal barrier coatings (TBCs) focusing mainly on issues of oxidation, erosion and foreign object damage (FOD). However, as the performance and durability of TBCs has improved the temperatures at which they operate has increased. This increase in temperature has resulted in another lifing issue for EB PVD TBCs, namely that of CMAS attack. Calcium–magnesium–alumino-silicate (CMAS) attack occurs when atmospheric dust that has deposited on the surface of turbine blades melts and wicks into the columns of the TBC. This occurs at temperatures above 1240–1260 °C and results in the degradation of the columnar microstructure of the TBCs. Due to the fact that TBCs operate in a temperature gradient CMAS only infiltrates part of the coating before solidifying.There are a number of issues associated with CMAS attack, both chemical and mechanical. From a chemical point of view CMAS attack of electron beam (EB) physical vapour deposited (PVD) TBCs can be considered as a form of corrosion; when there is a lot of excess CMAS on the surface of a coated component Yttria diffuses out of the TBC into the molten CMAS resulting in a t′ to monoclinic phase transformation in the yttria stabilised zirconia (YSZ), CMAS attack also results in localised melting and subsequent re-precipitation of the coating resulting in a loss of the defined columnar microstructure. While from a mechanical point of view the CMAS, once re-solidified, reduces the strain compliance of the EB PVD and can result in spallation of the TBC on cooling. Furthermore, current studies have indicated that small amount of CMAS infiltration significantly increases the erosion rate of EB PVD TBCs.This paper covers various aspects of CMAS attack of EB PVD TBCs, specifically looking at minimum levels of CMAS required to initiate damage, as well as investigating it from an erosion–corrosion perspective.     

大气等离子喷涂热障涂层CMAS防护层成分及厚度优化

目的优化热障涂层(TBCs)CMAS(CaO-MgO-Al_2O_3-SiO_2)阻抗层的成分和厚度,使其能有效阻抗CMAS沉积物的腐蚀,并同时与热障涂层有较高的结合力。方法首先利用多孔无压烧结陶瓷块体研究了不同含量Al_2O_3和8YSZ(8wt.%氧化钇稳定氧化锆)均匀混合后在高温(1250℃)条件下对CMAS沉积物的防护作用。采用扫描电子显微镜(SEM)、能谱仪(EDS)以及X射线衍射(XRD)仪,分析研究了CMAS腐蚀层的显微结构、腐蚀深度及反应产物。其次,基于最优成分,利用大气等离子喷涂(APS)制备了具有8YSZ/Al_2O_3陶瓷层的热障涂层。对CMAS腐蚀厚度进行分析测量,提出CMAS阻抗层的厚度。结果 Al_2O_3的添加可以有效地阻碍CMAS的渗入,并且Al_2O_3含量越多,防护效果越好。但是CMAS的渗入深度和氧化铝的添加量呈非线性关系。结合TBC陶瓷层的热学性能和力学性能的要求,本实验中最佳的TBCs复合陶瓷层组分为70wt%8YSZ+30wt%Al_2O_3。基于实验结果,提出YSZ/Al_2O_3复合陶瓷层(50μm)-YSZ陶瓷层(150μm)的双层TBC陶瓷层结构,并综合计算出复合陶瓷层的热膨胀系数为9.93×10-6℃-1以及双层TBC陶瓷层的热导率为2.4 W/(m·K)。最后对Al_2O_3减缓CMAS腐蚀的机理进行了量化分析。结论 YSZ/Al_2O_3复合阻抗层的最优成分为70wt%8YSZ+30wt%Al_2O_3,厚度为50μm,能有效阻碍高温下CMAS腐蚀。     

Failure of Thermal Barrier Coatings Subjected to CMAS Attack

The effect of environmental deposits, such as calcium-magnesium-alumino-silicate (CMAS), on thermal barrier coatings (TBCs) of commercial grade was investigated in laboratory scale. A controlled CMAS infiltration was achieved through exposure of coatings to calibrated cement tape composites containing synthetic glass powder representative of CMAS. Tube furnace and cyclic thermal shock simulation equipment were utilized to melt the synthesized CMAS tape on coating surfaces. The resulting premature failures of coatings were investigated through study of the thermomechanical and thermochemical interactions between the coatings and CMAS deposit. It was found that the porous nature of the thermal-sprayed TBCs make them vulnerable to CMAS attack even before discernible chemical reaction starts. Possible mitigation approaches are proposed for a better coating life under such severe circumstances.     

Erosion Performance of Gadolinium Zirconate-Based Thermal Barrier Coatings Processed by Suspension Plasma Spray

7-8 wt.% Yttria-stabilized zirconia (YSZ) is the standard thermal barrier coating (TBC) material used by the gas turbines industry due to its excellent thermal and thermo-mechanical properties up to 1200 °C. The need for improvement in gas turbine efficiency has led to an increase in the turbine inlet gas temperature. However, above 1200 °C, YSZ has issues such as poor sintering resistance, poor phase stability and susceptibility to calcium magnesium alumino silicates (CMAS) degradation. Gadolinium zirconate (GZ) is considered as one of the promising top coat candidates for TBC applications at high temperatures (>1200 °C) due to its low thermal conductivity, good sintering resistance and CMAS attack resistance. Single-layer 8YSZ, double-layer GZ/YSZ and triple-layer GZdense/GZ/YSZ TBCs were deposited by suspension plasma spray (SPS) process. Microstructural analysis was carried out by scanning electron microscopy (SEM). A columnar microstructure was observed in the single-, double- and triple-layer TBCs. Phase analysis of the as-sprayed TBCs was carried out using XRD (x-ray diffraction) where a tetragonal prime phase of zirconia in the single-layer YSZ TBC and a cubic defect fluorite phase of GZ in the double and triple-layer TBCs was observed. Porosity measurements of the as-sprayed TBCs were made by water intrusion method and image analysis method. The as-sprayed GZ-based multi-layered TBCs were subjected to erosion test at room temperature, and their erosion resistance was compared with single-layer 8YSZ. It was shown that the erosion resistance of 8YSZ single-layer TBC was higher than GZ-based multi-layered TBCs. Among the multi-layered TBCs, triple-layer TBC was slightly better than double layer in terms of erosion resistance. The eroded TBCs were cold-mounted and analyzed by SEM.     

Study of microstructure and thermal shock behavior of two types of thermal barrier coatings

Gas turbines provide one of the most severe environments challenging material systems nowadays. Only an appropriate coating system can supply protection particularly for turbine blades. This study was made by comparison of properties of two different types of thermal barrier coatings (TBCs) in order to improve the surface characteristics of high temperature components. These TBCs consisted of a duplex TBC and a five layered functionally graded TBC. In duplex TBCs, 0.35 mm thick yittria partially stabilized zirconia top coat (YSZ) was deposited by air plasma spraying and ～0.15 mm thick NiCrAlY bond coat was deposited by high velocity oxyfuel spraying. ～0.5 mm thick functionally graded TBC was sprayed by varying the feeding ratio of YSZ/NiCrAlY powders. Both coatings were deposited on IN 738LC alloy as a substrate. Microstructural characterization was performed by SEM and optical microscopy whereas phase analysis and chemical composition changes of the coatings and oxides formed during the tests were studied by XRD and EDX. The performance of the coatings fabricated with the optimum processing conditions was evaluated as a function of intense thermal cycling test at 1100 °C. During thermal shock test, FGM coating failed after 150 and duplex coating failed after 85 cycles. The adhesion strength of the coatings to the substrate was also measured. Finally, it is found that FGM coating has a larger lifetime than the duplex TBC, especially with regard to the adhesion strength of the coatings.     

基于磁过滤技术的热障涂层表面Al2O3 覆盖层抗CMAS腐蚀性能

为了提高热障涂层（TBC）的抗沉积物（主要成分为CaO、MgO、Al₂O₃和SiO₂,简称CMAS）腐蚀性能,采用磁过滤阴极真空电弧（FCVA）技术在TBC表面上制备了致密的Al₂O₃覆盖层,比较和分析了Al₂O₃改性TBC和沉积态TBC的润湿行为和抗CMAS腐蚀性能。结果表明：使用FCVA技术制备Al₂O₃覆盖层的过程对7%（质量分数）氧化钇稳定的氧化锆（7YSZ）相的结构无明显影响,且经Al₂O₃改性的TBC综合性能均优于沉积态TBC。在1250 ℃、CMAS腐蚀条件下,Al₂O₃覆盖层有效地限制了熔融CMAS在TBC表面上的扩散行为。同时,Al₂O₃填充了7YSZ柱状晶之间的间隔并且阻碍了熔融CMAS的渗透,证明了FCVA可作为一种制备Al₂O₃涂层的新方法以提高TBC的抗CMAS腐蚀性能,且Al₂O₃涂层及其制备过程对TBC的热震性能均无消极影响。     

Higher Temperature Thermal Barrier Coatings with the Combined Use of Yttrium Aluminum Garnet and the Solution Precursor Plasma Spray Process

Gas-turbine engines are widely used in transportation, energy and defense industries. The increasing demand for more efficient gas turbines requires higher turbine operating temperatures. For more than 40 years, yttria-stabilized zirconia (YSZ) has been the dominant thermal barrier coating (TBC) due to its outstanding material properties. However, the practical use of YSZ-based TBCs is limited to approximately 1200 °C. Developing new, higher temperature TBCs has proven challenging to satisfy the multiple property requirements of a durable TBC. In this study, an advanced TBC has been developed by using the solution precursor plasma spray (SPPS) process that generates unique engineered microstructures with the higher temperature yttrium aluminum garnet (YAG) to produce a TBC that can meet and exceed the major performance standards of state-of-the-art air plasma sprayed YSZ, including: phase stability, sintering resistance, CMAS resistance, thermal cycle durability, thermal conductivity and erosion resistance. The temperature improvement for hot section gas turbine materials (superalloys & TBCs) has been at the rate of about 50 °C per decade over the last 50 years. In contrast, SPPS YAG TBCs offer the near-term potential of a > 200 °C improvement in temperature capability.