声发射技术在热障涂层失效机理中的研究进展及展望

热障涂层（TBCs）具有优异的高温抗氧化、高温力学和抗热腐蚀性能而备受关注,广泛应用于航空发动机和燃气轮机热端部件中。热障涂层服役环境的恶劣和涂层体系结构的复杂,极易导致涂层发生界面分层或剥落失效,因此通过对热障涂层的裂纹萌生和扩展问题进行实时监测,对于失效机理研究显得尤为重要。简述光激发荧光压电光谱（PLPS）、红外热成像（IRT）、阻抗谱（IS）的原理及其在热障涂层失效行为研究中的应用,重点介绍声发射技术在热障涂层失效机理方面的研究成果。基于声发射的热障涂层失效过程的信号分析和深度处理,结合声发射技术在热障涂层中的参数分析和波形分析,对热障涂层失效过程及失效形态进行模式识别,通过损伤程度的定量评估来进行热障涂层的寿命预测。对声发射技术在热障涂层失效预测及寿命评估指明了方向,并创新性地对未来声发射技术在热障涂层的疲劳损伤方面研究趋势提出展望。     

应变幅和相角度对热障涂层材料系统热机械疲劳性能的影响（英文）

热障涂层作为燃气轮机高温部件的关键材料,其服役过程中的脱落与失效机理一直是研究的热点问题。研究了应变幅和相角度对含热障涂层的镍基高温合金热机械疲劳性能的影响。研究结果表明,在相同相角度下,热机械疲劳寿命随应变幅的增大而降低。固定应变幅,同相位下样品的热机械疲劳寿命要高于反相位样品。所有样品中,裂纹萌生于热生长氧化物层,在粘结层与陶瓷层界面扩展形成分层裂纹,分层裂纹与陶瓷层内贯穿裂纹连接起来导致大面积的陶瓷层剥落,从而导致TBC层失效。另外,分析了热障涂层中的应力分布,初步建立了含热障涂层的镍基高温合金热机械疲劳寿命模型,发现含热障涂层的镍基高温合金热机械疲劳寿命与涂层中的最大应力呈指数关系。     

应变幅和相角度对热障涂层材料系统热机械疲劳性能的影响

热障涂层作为燃气轮机高温部件的关键材料,其服役过程中的脱落与失效机理一直是研究的热点问题。本文主要研究了应变幅和相角度对含热障涂层的镍基高温合金热机械疲劳性能的影响。研究结果表明,在相同相角度下,热机械疲劳寿命随应变幅的增大而降低。固定应变幅,同相位下样品的热机械疲劳寿命要高于反相位样品。所有样品中,裂纹萌生于热生长氧化物层,在粘结层与陶瓷层界面扩展形成分层裂纹,分层裂纹与陶瓷层内贯穿裂纹连接起来导致大面积的陶瓷层剥落,从而导致TBC层失效。另外,本文分析了热障涂层中的应力分布,初步建立了含热障涂层的镍基高温合金热机械疲劳寿命模型,发现含热障涂层的镍基高温合金热机械疲劳寿命与涂层中的最大应力呈指数关系。     

高温拉压环境下DZ125高温合金的热障涂层失效

采用电子束物理气相沉积法（EB-PVD）在定向凝固Ni基高温合金DZ125基体上制备了NiCoCrAlY粘结层和YSZ陶瓷层，研究了高温拉压环境下热障涂层的失效模式，并对其进行了有限元分析。实验结果表明，热障涂层的失效与仅受热载荷作用下的有很大不同，仅有热载荷作用下的热障涂层裂纹多萌生于热氧化层（TGO）内部，进而扩展引起热障涂层的失效。而高温拉压试验后热障涂层体系存在两种裂纹，分别萌生于TGO／粘结层界面和粘结层／扩散层界面附近。有限元模拟结果显示TGO／陶瓷层和TGO／粘结层处存在应力状态的转变和应力值的突变，径向应力的突变导致了界面分离现象的产生，而轴向应力的突变加速了垂直于界面裂纹的扩展，并导致了试样的最终断裂。     

热障涂层的制备及其失效的研究现状

热障涂层作为航空发动机和燃气轮机高温部件的保护涂层,其抗高温失效能力直接决定了部件的工作效率和寿命.回顾热障涂层的发展历史及研究现状,着重介绍了热障涂层的主要制备方法及其相应涂层的结构特征,综述了各类热障涂层失效的影响因素和失效机理.     

热障涂层的研究现状与发展趋势

热障涂层是一类高温防护涂层,由于其应用的广泛性,已成为近年来涂层研究领域的热点之一。对热障涂层国内外的研究进展进行了综述,重点阐述热障涂层成分的选择、热障涂层的结构设计、热障涂层的制备工艺、热障涂层的失效机理、寿命预测以及热障涂层的发展趋势。     

中科院长春应化所热障涂层的设计和失效机理研究获进展

正日前,中科院长春应用化学研究所在热障涂层的设计思路、失效机理以及新型热障涂层材料研发等方面取得新进展,设计并成功制备出使用温度≥1250℃的双陶瓷层热障涂层材料,"热障涂层的设计和失效机理研究"成果荣获2013年吉林省自然科学奖一等奖。热障涂层技术利用陶瓷材料的高隔热性和耐腐蚀性来保护金属基底,在能源、航空、航天等方面都有重大应用价值。常规热障涂层材料8YSZ(8wt%Y_2 O_3稳定化的ZrO_2)因在高温下发生相变、烧结和透氧,不能承受1 200℃以上的高温。目前,世界各国都在努力研究能替代8YSZ、在更高温度下使用的热障涂层材料。     

四点弯曲条件下热障涂层断裂模式的声发射表征

采用声发射技术实时监测喷涂态8% Y₂O₃稳定的ZrO₂（8YSZ）在四点弯曲载荷下的损伤断裂行为。采用特征参数分析、聚类分析和小波包变换分析声发射信号结合涂层的微观形貌和应力状态,从而推测出热障涂层系统的失效形式。结果表明：内弯和外弯两种加载模式下,均各有4种失效行为。宏观断裂对应的剥落信号无明显频带,而基底变形、表面垂直裂纹、张开型界面裂纹和剪切型界面裂纹信号对应的主频带可清晰区分为：0~156.25 kHz、156.25~234.375 kHz、312.625~390.625 kHz和390.625~468.75 kHz。热障涂层在外弯载荷下,表面垂直裂纹不断出现,随后扩展到粘结层-陶瓷层界面处并转化为张开型界面裂纹;而在内弯载荷下,则在粘结层-陶瓷层界面附近产生剪切型界面裂纹,仅出现少量的表面垂直裂纹。两种界面裂纹均会引起热障涂层的宏观裂纹和剥落。     

含垂直裂纹的厚热障涂层的热稳定性及力学性能(英文)

采用循环热暴露及热震试验研究含或不含垂直裂纹的厚热障涂层的热稳定性和失效机制。先采用空气等离子喷涂技术在基体表面制备150μm厚的连接涂层,再在该涂层上采用空气等离子喷涂技术制备2000μm厚的热障涂层。含或不含垂直裂纹的热障涂层的粘附强度分别为24.7和11.0 MPa,表明含垂直裂纹的热障涂层的界面稳定性更高。循环热暴露及热震试验表明其热稳定性更高。含或不含垂直裂纹的热障涂层的硬度分别为6.6和5.3GPa,经循环热暴露试验后分别升高至9.5和5.5 GPa。实验表明上层涂层中垂直裂纹的存在有利于延长热障涂层高温环境的寿命。     

等离子喷涂ZrO2-NiCoCrAlY梯度热障涂层的抗热震性及失效机理

研究了ZrO2-NiCoCrAlY热障涂层的抗热震性和热震失效机理.实验结果表明,梯度热障涂层能明显延缓热震裂纹的形成和扩展,具有较高的抗热震性.热震裂纹形成与扩展主要在粘结层与基体的界面处.随热循环次数的增加,热震裂纹可在表面陶瓷层内和陶瓷层与过渡层的界面处形成.实验表明热障涂层热震失效的过程主要是裂纹形成、扩展及涂层剥落,粘结层的氧化是导致涂层剥落失效的重要原因.     

TBC experience in land- based gas turbines

This paper summarizes prior and on-going machine evaluations of thermal barrier coatings (TBC) for power generation, that is large industrial gas turbine applications. Rainbow testing of TBCs on turbine nozzles, shrouds, and buckets are described along with a test of combustor liners. General Electric Power Generation has conducted more than IS machine tests on TBC turbine nozzles with various coatings. TBC performance has been quite good, and additional testing, including TBCs on shrouds and buckets, is continuing. Included is a brief comparison of TBC requirements for power generation and aircraft turbines.     

PVD TBC experience on GE aircraft engines

The higher performance levels of modern gas turbine engines present significant challenges in the reli-ability of materials in the turbine. The increased engine temperatures required to achieve the higher per-formance levels reduce the strength of the materials used in the turbine sections of the engine. Various forms of thermal barrier coatings have been used for many years to increase the reliability of gas turbine engine components. Recent experience with the physical vapor deposition process using ceramic material has demonstrated success in extending the service life of turbine blades and nozzles. Engine test results of turbine components with a 125 μm (0.005 in.) PVD TBC have demonstrated component operating tem-peratures of 56 to 83 °C (100 to 150 °F) lower than non-PVD TBC components. Engine testing has also revealed that TBCs are susceptible to high angle particle impact damage. Sand particles and other engine debris impact the TBC surface at the leading edge of airfoils and fracture the PVD columns. As the impacting continues, the TBC erodes in local areas. Analysis of the eroded areas has shown a slight increase in temperature over a fully coated area ; however, a significant temperature reduc-tion was realized over an airfoil without TBC.     

重型燃机喷嘴壳体及遮热板热障涂层剥落机制

目的 探究重型燃机喷嘴壳体及遮热板热障涂层剥落机制,为该部件的全寿命管理提供参考。方法 采用等离子喷涂方法,分别制备以06Cr25Ni20不锈钢和Hastelloy X合金为基材的热障涂层试验件,并结合水淬热冲击表征方法与瞬态热力耦合仿真方法,表征热障涂层水淬后的剥落状态,获得热障涂层残余剪应力的分布状态随基材和服役工况的变化行为,揭示热障涂层在多层热失配工况下的剥落机制。结果 在水淬热冲击条件下,2种不同基材的热障涂层试验件表现出类似的剥落行为,但由于基材热膨胀系数的差异,以06Cr25Ni20不锈钢为基材的热障涂层的残余剪应力(70.1 MPa)比Hastelloy X合金基材的热障涂层(52.7 MPa)更大,热冲击寿命更短。在梯度温度载荷下,2种不同基材热障涂层试验件的失效模式不同,前者的最大残余剪应力为39.2 MPa,后者为25.7 MPa。结论 在2种温度载荷下,以Hastelloy X合金为基材的热障涂层具有较低的残余应力和较长的服役寿命。此外,水淬热冲击可以快速表征热障涂层的寿命行为,但其失效模式与实际梯度温度载荷下的失效模式仍有一定区别。     

等离子蒸发沉积热障涂层抗CMAS附着研究进展

热障涂层是先进航空发动机核心热端部件高压涡轮叶片的关键技术,随着发动机服役温度的不断提高,一种主要化学成分为CaO-MgO-Al2O3-SiO2(简称CMAS)的环境沉积物对叶片的危害日益严重,不仅堵塞叶片表面气膜冷却孔,影响叶片冷效,而且导致热障涂层早期剥落失效,服役寿命大幅度降低。高温熔融CMAS在涂层表面的附着过程及防护方法是目前热障涂层研究领域的热点和难点。本文针对新型的等离子蒸发沉积技术,梳理了近年来国内外学者在热障涂层抗CMAS附着、渗入和腐蚀方面的最新研究成果,指出了涂层抗CMAS侵蚀研究的发展方向。     

Commercial thermal barrier coatings with a double-layer bond coat on turbine vanes and the process repeatability

An investigation was conducted to develop a commercial thermal barrier coating (TBC) system with a double-layer bond coat on Ni-base superalloy turbine vanes. Surface morphology and cross-section microstructure of the developed coatings were studied by using Optical Microscope and Scanning Electron Microscope (SEM). Experimental and production results showed that a TBC system with good adherence and a repeatable process to apply the coatings were obtained. Furthermore, the repeatability of the vapor phase coating process, high velocity oxy-fuel (HVOF), and air plasma spray (APS) process were discussed. Finally, the advantage and the future possible improvement of the investigated TBC system were also proposed.     

Damage mechanisms and lifetime behavior of plasma sprayed thermal barrier coating systems for gas turbines—Part I: Experiments

Detailed damage analyses of a plasma sprayed ZrO₂/8 wt.-% Y₂O₃-MCrAlY-CMSX-4 TBC system during isothermal and cyclic oxidation tests with different dwell times at high temperature have been performed. The resulting failure mode, i.e. the particular delamination crack path, is strongly dependent on the temperature cycle applied. Isothermal exposure promotes crack propagation within the TGO, whereas thermal cycling shifts the crack path towards the TBC. Thermal cycling with dwell time at high temperature leads to a mixed delamination crack path (partly within TBC and TGO). The respective correlation between TBC lifetimes and duration of high temperature dwell time per cycle (cycle frequency) is shown and discussed.     

Investigation by 3D FE simulations of delamination crack initiation in TBC caused by alumina growth

In gas turbines, thermal barrier coatings (TBCs) applied by air plasma spraying are widely used to reduce the temperature in hot components. The TBC allows higher gas temperature and/or reduces the need for internal cooling in the hot components, thus increasing the efficiency of the gas turbine. Spallation is a common failure mechanism of TBC and occurs after a critical number of thermal cycles, when the alumina layer has grown to a critical thickness. The influence of the growing alumina layer and the top/bond-coat interface roughness in the TBC has been investigated. The primary goal was to identify failure mechanisms that can be incorporated into a life model of the TBC, and to increase the understanding of the delamination process in the TBC. A new formulation of alumina growth is proposed, in which the swelling strains caused by the volumetric increase during alumina growth depends on the stress state. The alumina growth model is used in 3D FE thermal cycling simulations of a TBC in which the thermal cycle time is long enough to characterize a typical cycle of a gas turbine. From the simulations, the growing alumina layer is observed to be one failure mechanism of the TBC. Without an alumina layer in the model, high delamination stress is observed at room temperature, above ridges of the top/bond-coat interface in the top coat. When the alumina is growing, the point of maximum delamination stress is moved towards the valleys. When the thickness of the alumina layer has grown to approximately 8–10 μm, positive delamination stress is found above the valleys in the top coat. The movement of the positive delamination stress region can explain why a delamination crack develops, which will cause spallation of the TBC during shutdown to room temperature.     

Evidence of accelerated thermal cycling test schedules influencing the ranking of zirconia-base thermal barrier coatings

Thermal barrier coatings (TBCs) often encounter temperature cycling in the course of normal operation. In the absence of actual or simulated engine test facilities, accelerated furnace thermal cycling experiments are frequently devised to evaluate the response of various TBCs. This study, which deals with yttria-stabilized and magnesia-stabilized zirconia systems, shows that the performance of a TBC is significantly governed by the severity of the time-temperature schedule employed. More importantly, the ranking of the two zirconia-base TBCs also is influenced by the adopted thermal cycling test schedule. These findings have ramifications in the design of suitable accelerated tests for TBC evaluation.     

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.