等离子喷涂ZrO2-8%Y2O3热障涂层的组织与性能研究

采用超音速火焰喷涂粘结层、大气等离子喷涂陶瓷层制备了双层结构的热障涂层。利用扫描电镜对热障涂层进行了微观组织结构分析,主要对涂层的热导率及隔热性能进行了试验研究。结果表明：陶瓷层与粘结层、粘结层与基体的结合良好;陶瓷涂层在1100℃下的热导率为0.99W/（m·K）;在测试温度为1100℃、冷气流量为4m3/h的条件下,隔热效果可达到155℃。     

Erosion, corrosion and erosion–corrosion of EB PVD thermal barrier coatings

Electron beam (EB) physical vapour deposited (PVD) thermal barrier coatings (TBCs) have been used in gas turbine engines for a number of years. The primary mode of failure is attributed to oxidation of the bond coat and growth of the thermally grown oxide (TGO), the alumina scale that forms on the bond coat and to which the ceramic top coat adheres. Once the TGO reaches a critical thickness, the TBC tends to spall and expose the underlying substrate to the hot gases. Erosion is commonly accepted as a secondary failure mechanism, which thins the TBC thus reducing its insulation capability and increasing the TGO growth rate. In severe conditions, erosion can completely remove the TBC over time, again resulting in the exposure of the substrate, typically Ni-based superalloys. Since engine efficiency is related to turbine entry temperature (TET), there is a constant driving force to increase this temperature. With this drive for higher TETs comes corrosion problems for the yttria stabilised zirconia (YSZ) ceramic topcoat. YSZ is susceptible to attack from molten calcium–magnesium–alumina–silicates (CMAS) which degrades the YSZ both chemically and micro-structurally. CMAS has a melting point of around 1240 °C and since it is common in atmospheric dust it is easily deposited onto gas turbine blades. If the CMAS then melts and penetrates into the ceramic, the life of the TBC can be significantly reduced. This paper discusses the various failure mechanisms associated with the erosion, corrosion and erosion–corrosion of EB PVD TBCs. The concept of a dimensionless ratio D/d, where D is the contact footprint diameter and d is the column diameter, as a means of determining the erosion mechanism is introduced and discussed for EB PVD TBCs.     

Microstructure and Oxidation Behaviors of Nano-particles Strengthened NiCoCrAlY Cladded Coatings on Superalloys

Nano-particles which can largely improve the microstructure and oxidation resistance of materials are often used as a strengthening component in metal matrix composites. However, few studies were reported on its application in the bond coat of duplex structure thermal barrier coating(TBC). Three kinds of NiCoCrAlY coatings strengthened by different nano-particles with the same addition (1%, mass fraction) were prepared by the laser cladding technique on Ni-based superalloy substrates, aiming to study the effects of the nano-particles on microstructure and oxidation resistance of NiCoCrAlY coatings (the bond coat of the duplex structure thermal barrier coatings). Scanning electron microscope (SEM), X-ray diffractometer(XRD) and thermogravimetry were employed to investigate their morphologies, phases and cyclic oxidation behaviors in atmosphere at 1 050℃, compared with the coating without nano-particles. With the addition of nano-particles, the growth pattern of the grains at the interface changed from epitaxial growth to non-epitaxial growth or part-epitaxial growth; slender dendrites were broken and cellularized; cracks and pores were restrained; and the oxidation weight-gain and the stripping resistance of the oxide scale were improved as well. Among the three kinds of nano-particles, the SiC nano-particles showed the most improvement on microstructure, while the CeO2 nano-particles were insufficient, but its effects on the oxidation resistance are the same as those of the SiC nano-particles. Based on the discussions of the influence mechanism, it is believed that CeO2 nano-particles would show better improvement than SiC nano-particles if the proper amount is added and the proper preparation technique of micro-nanometer composite powders is adopted, with the synergistic action of nanometer effect and reactive element effect.     

The effect of TBC morphology and aging on the erosion rate of EB-PVD TBCs

Since thermal barrier coatings (TBCs) have been used in gas turbines most of the research conducted on them has involved the bond coat and the growth of the thermally grown oxide (TGO) as failure of the bond coat and the TGO were considered to be the primary causes of failure. Erosion of TBCs has been considered as a secondary problem and as such received less attention. Most of the initial work on the erosion of TBCs covered the effects of velocity and impact angle on the erosion rates of both plasma sprayed (PS) and electron beam physical vapour deposited (EB-PVD) TBCs and compared the differences between the two deposition systems. It must be noted that most of the tests were conducted on coatings in the as received condition. This paper aims at expanding the understanding of the erosion of EB-PVD TBCs by examining the effects of TBC morphology, column diameter, column inclination angle and the effects of aging and sintering on the erosion rates of EB-PVD TBCs. The paper also looks at how erosion rate changes as the coating is eroded through to the bond coat.The paper also looks at the mechanisms of foreign object damage of EB-PVD TBCs under a range of different impact conditions. The different damage mechanisms have been identified and related to the size and impact velocity of the impacting particles. The effect of temperature on the plasticity and hence the mechanisms are also discussed, while mapping is used to set the boundary limits for the different types of damage mechanisms that have been identified. It was found that at temperatures above 800 °C the coatings can accommodate a large degree of plastic deformation, while at room temperature there is a greater degree of cracking, for similar types of FOD impact. The 800 °C is not necessarily a limit, but the temperature at which the coatings were tested, and the limiting temperature could in fact be significantly lower. It was found that, all else being equal, erosion rate decreases with a decrease in the column diameter, while aging results in an increase in the erosion rate, dependent on the aging temperature and time. A decrease in the inclination angle of the columns with respect to the substrate increases the erosion rate, when the inclination angle is less than 60° the erosion rate increases catastrophically. These effects are all discussed and explained in terms of erosion mechanisms and mechanical properties in the paper.     

双送粉激光熔覆CoCrAlSiY/YSZ梯度涂层微观组织及热振性能

采用双送粉方式,利用激光熔覆技术在TC4基体上制备CoCrAlSiY/Y2O3-ZrO2（YSZ）梯度涂层。对CoCrAlSiY/YSZ梯度涂层的微观组织、元素分布、显微硬度及热振性能进行了分析与研究,结果表明：梯度涂层与基体结合紧密,各梯度亚层之间不存在明显的界面,梯度涂层无明显裂纹,形成了良好的冶金结合;随着YSZ含量的提高,梯度涂层显微硬度呈梯度变化。在750 ℃下进行了不同循环周期的热振试验,试验结果表明CoCrAlSiY/YSZ梯度涂层具有一定的抗热振性。     

Time of flight improved thermally grown oxide thickness measurement with terahertz spectroscopy

As a nondestructive testing technique, terahertz time-domain spectroscopy technology is commonly used to measure the thickness of ceramic coat in thermal barrier coatings (TBCs). However, the invisibility of ceramic/thermally grown oxide (TGO) reflective wave leads to the measurement failure of natural growth TGO whose thickness is below 10 μm in TBCs. To detect and monitor TGO in the emergence stage, a time of flight (TOF) improved TGO thickness measurement method is proposed. A simulative investigation on propagation characteristics of terahertz shows the linear relationship between TGO thickness and phase shift of feature wave. The accurate TOF increment could be acquired from wavelet soft threshold and cross-correlation function with negative effect reduction of environmental noise and system oscillation. Thus, the TGO thickness could be obtained efficiently from the TOF increment of the monitor area with different heating times. The averaged error of 1.61 μm in experimental results demonstrates the highly accurate and robust measurement of the proposed method, making it attractive for condition monitoring and life prediction of TBCs.     

热障涂层折射率与厚度的太赫兹无损检测

精确提取陶瓷层（Top coat,TC）与热生长氧化层（Thermally grown oxide,TGO）层在太赫兹频段的折射率是进行热障涂层（Thermal barrier coatings,TBCs）太赫兹无损检测研究的重要条件。由于对涂层样品只能采取反射式测量,所以首先比较了反射式与传统透射式测量条件下提取样品太赫兹光学参数及厚度的结果,随后利用反射式太赫兹时域脉冲成像系统提取等离子体喷涂的8YSZ热障涂层（TBCs）中TC层与TGO层的折射率,并依据所提取折射率进一步对TC层的厚度分布进行测量及成像。试验结果表明在材料中衰减较小的有效频段下反射式测量同样可以精确提取样品的折射率以及厚度,反射式测量TC层的平均折射率为5.23,TGO层的折射率为2.91,TGO的主要成分α-Al₂O₃的折射率为2.85。TBCs样品中TC层的平均厚度为257 μm,从TC层厚度的太赫兹图像中可观察到TC与粘结层（Bond coat,BC）界面的不均匀程度。反射式太赫兹无损检测可精确提取TBCs中TC与TGO的折射率和厚度,这对于TBCs中裂纹和气泡等缺陷的识别以及TGO生长太赫兹检测具有重要意义。     

Effect of TGO on the tensile failure behavior of thermal barrier coatings

Frontiers of Mechanical Engineering - Thermally grown oxide (TGO) may be generated in thermal barrier coatings (TBCs) after high-temperature oxidation. TGO increases the internal stress of the...     

Modeling Temperature Distributions in Thermal Barrier Coatings with Various Thicknesses

The geometric model of thermal barrier coatings (TBCs) was established. Two cases based on the standard thickness of the ceramic layer existed. These were the steps of TBCs thickness were being higher than the standard layer and those of lower than standard layer. The heat transfer processes of these two cases were simulated with the ANSYS software. The change process of thermal effusivity was analyzed in the two cases and the coating thickness differences effect on the surface temperature distributions of TBCs was analyzed through the time course curves of temperature difference. Moreover, the difficulty of detection for these two cases with infrared nondestructive testing was discussed according to maximum temperature difference and the maximum temperature contrast ratio. The result demonstrated that all curves of thermal effusivity with various thickness differences coincided with each other at the initial and longer times, where the ceramic layer thickness was lower than the standard layer. This was more easily detectable compared to the higher thickness and the maximum temperature contrast ratio or the maximum temperature difference increased as the coating thickness difference increased.     

热障涂层在多次热循环作用下残余应力的模拟

采用热弹塑性有限元方法,对热障涂层多次热循环降温过程中由于热梯度和材料参数不匹配而产生的残余应力进行了数值模拟,分析了平面和曲面的界面形貌对界面残余应力的影响.结果表明,在相同材料参数情况下,陶瓷层与粘接层的界面形状对残余应力及结构稳定状态有显著的影响,凹凸不平的界面将会使界面残余应力发生突变,不利于增强界面结合强度和涂层结构的热稳定性.该结果对分析涂层寿命及失效机制有指导意义.     

真空退火对磁控溅射CuS-MoS2涂层润滑性能的影响

为提高MoS2润滑涂层承载力和抗湿性能,使用磁控溅射技术制备CuS掺杂MoS2复合涂层,并对制备涂层进行220、320和420℃真空退火处理,以发挥CuS与MoS2协同润滑作用。采用场发射扫描电子显微镜、激光拉曼光谱分析涂层结构,通过洛氏硬度压痕试验、摩擦磨损试验和纳米压痕试验对涂层性能进行分析。实验结果表明:随CuS靶溅射功率提高,涂层中出现颗粒长大和CuS结晶化趋势,且CuS掺杂抑制了MoS 2形核长大,涂层膜-基结合力有所下降;真空退火处理后CuS-MoS2复合涂层表面发生分解,厚度明显降低,MoS2(002)相形核长大,摩擦学性能得到提升;320℃退火处理后涂层在常温和RH70%大气环境下获得最低平均摩擦因数0.08,纳米硬度达到5.64 GPa,并具有较好的耐磨损性能。研究认为由于CuS受热分解导致复合涂层结构和成分变化,生成了有利于发挥CuS与MoS2协同润滑效应的微晶相,使得涂层润滑性能得到明显提升。     

热循环下热障涂层结构不稳定性的数值模拟

针对多次热循环工作条件下热障涂层的结构不稳定问题,采用热弹塑性有限元方法,对不规则界面形貌的涂层结构进行安定性分析.分析了不同的BC层屈服强度对涂层循环不稳定性的影响.结果表明,在温度场和界面形貌相同的条件下BC的屈服强度决定系统的稳定性.该结果对分析涂层体寿命及失效机制有指导意义.     

Effect of microstructure and temperature on the erosion rates and mechanisms of modified EB PVD TBCs

Thermal barrier coatings (TBCs) have now been used in gas turbine engines for a number of decades and are now considered to be an accepted technology. As there is a constant drive to increase the turbine entry temperature, in order to increase engine efficiency, the coatings operate in increasingly hostile environments. Thus there is a constant drive to both increase the temperature capabilities of TBCs while at the same time reducing their thermal conductivities. The thermal conductivity of standard 7 wt% yttria stabilized zirconia (7YSZ) electron beam (EB) physical vapour deposited (PVD) TBCs can be reduced in two ways: the first by modification of the microstructure of the TBC and the second by addition of ternary oxides. By modifying the microstructure of the TBC such that there are more fine pores, more photon scattering centres are introduced into the coatings, which reduce the heat transfer by radiation. While ternary oxides will introduce lattice defects into the coating, which increases the phonon scattering, thus reducing the thermal conductivity via lattice vibrations. Unfortunately, both of these methods can have a negative effect on the erosion resistance of EB PVD TBCs.This paper compares the relative erosion rates of ten different EB PVD TBCs tested at 90° impact at room temperature and at high temperature and discusses the results in term of microstructural and temperature effects. It was found that by modifying the coating deposition, such that a low density coating with a highly ‘feathered’ microstructure formed, generally resulted in an increase in the erosion rate at room temperature. When there was a significant change between the room temperature and the high temperature erosion mechanism it was accompanied by a significant decrease in the erosion rate, while additions of dopents was found to significantly increase the erosion rate at room and high temperature. However, all the modified coatings still had a lower erosion rate than a plasma sprayed coatings. So, although, relative to a standard 7YSZ coating, the modified coatings have a lower erosion resistance, they still perform better than PS TBCs and their lower thermal conductivities could make them viable alternatives to 7YSZ for use in gas turbine engines.     

Evolution of residual stresses in micro-arc oxidation ceramic coatings on 6061 Al alloy

Most researches on micro-arc oxidation mainly focus on the application rather than discovering the evolution of residual stresses. However, residual stresses in the surface coatings of structural components have adverse effects on their properties, such as fatigue life, dimensional stability and corrosion resistance, etc. The micro-arc oxidation ceramic coatings are produced on the surfaces of 6061 aluminum alloy by a homemade asymmetric AC type of micro-arc oxidation equipment of 20 kW. A constant current density of 4.4___0.1 A/dm2 and a self-regulated composite electrolyte are used. The micro-arc oxidation treatment period ranges from 10 min to 40 min, and the thickness of the ceramic coatings is more than 20 Bin. Residual stresses attributed to 7-A1203 constituent in the coatings at different micro-arc oxidation periods are analyzed by an X-ray diffractometer using the sin2~u method. The analysis results show that the residual stress in the ceramic coatings is compressive in nature, and it increases first and then decreases with micro-arc oxidation time increase. The maximum stress value is 1 667_＋20 MPa for period of 20 min. Through analyzing the coating thickness, surface morphology and phase composition, it is found that the residual stress in the ceramic coatings is linked closely with the coating growth, the phase composition and the micro cracks formed. It is also found that both the heat treatment and the ultrasonic action release remarkably the residual compressive stress. The heat treatment makes the residual compressive stress value decrease 1 378 MPa. The ultrasonic action even alters the nature of the residual stress, making the residual compressive stress change into a residual tensile stress.     

EB—PVD热障涂层皱曲问题研究进展

热障涂层皱曲是指在高温循环载荷下陶瓷表层／粘结层界面甚至陶瓷层表面发生的凸起或凹陷现象。综合国内外最新的有关皱曲现象的报道,系统地介绍了电子束物理气相沉积（EB—PVD）热障涂层皱曲行为。综述了皱曲的特点、研究历史和研究进展,从微观机理、研究方法和皱曲对涂层性能影响3个方面进行了分析,指出了可行的研究发展方向。     

Influence of DLC coating thickness on tribological characteristics under sliding rolling contact condition

Diamond-like-carbon (DLC) coating of thickness 3 and 10 μm were developed with and without radical nitriding pretreatment on steel rollers and spur gear pair. The friction coefficient and wear amount were evaluated under sliding rolling contact condition in vacuum and under oil lubrication. Delamination of coatings was observed at the interface of the substrate. The wear resistance of coatings improved with the thickness of the coating. In vacuum both the roller and the gear pair of 10 μm coating thickness with radical nitriding showed identical wear behavior. The radical nitriding seemed to enhance the life of DLC coatings.     

Nb/NbCr2合金表面激光熔覆抗氧化涂层的研究进展

高强高韧Nb/NbCr2合金较差的高温抗氧化性限制了其作为高温结构材料在1 200℃以上的应用进程,本文对NbCr2基合金的高温抗氧化性的研究现状及其高温抗氧化涂层的研究进展进行了综合评述,着重介绍了激光熔覆纳米陶瓷抗氧化涂层存在的问题及发展趋势,并就今后发展方向提出了看法。     

表面加工多晶硅薄膜热扩散系数在线测试结构

基于目前已有的真空桥式薄膜热扩散系数测试结构和测试方法，综合考虑辐射、对流以及向衬底的传热等因素的影响，从而使得本文设计的测试结构和提取方法更具有实际价值。文中通过分析两个长度不同，但宽度与厚度相同的梁在相同加热电流下的瞬态电阻变化特性，来提取多晶硅薄膜的热扩散系数。同时利用有限元分析软件ANSYS进行了模拟分析，分析表明模拟提取值与理论值较好地吻合，从而验证了模型建立的正确性，说明该方法能够实现对多晶硅薄膜热扩散系数的在线提取，且具有较高的测试精确度。     

Laser flash method for measuring thermal conductivity of liquids-application to low thermal conductivity liquids

A laser flash method developed for the measurement of thermal conductivity of solids was applied to liquids of low thermal conductivity. The sample liquid was sandwiched in between a small thin metal disk and a sample holder. When the laser beam is absorbed in the front surface of the metal disk, the temperature of the disk quickly rises about 2 K and heat then flows downwards through the sample liquid as one-dimensional heat flow. The thermal conductivity of liquid can be obtained from the temperature fall of the disk without employing any reference materials and also without measuring the thickness of the sample liquid layer. Thermal conductivities of water and toluene near room temperature were measured by this method with a mean deviation of 2.6%. This laser flash method may be applied to the measurement of the thermal conductivity of liquids such as molten salts at elevated temperatures.     

Development of oxide based diffusion barrier coatings for CFC components applied in modern furnaces

Carbon fibre reinforced carbon (CFC) materials show a high potential for usage in furnaces as sample carriers for example, which is due to their excellent thermal stability compared to steel carriers. Only their tendency to react with different metals at high temperatures by C-diffusion is a disadvantage, which can be solved by application of diffusion barriers. In order to enable the utilization of CFC-carriers for e.g. brazing furnaces, within the frame of this study thermally sprayed diffusion barrier coatings were developed. Coatings of mullite and ZrO₂-7%βY₂O₃ (YSZ) were prepared by air plasma spraying (APS). The coatings were investigated in terms of their microstructure and thermal shock behaviour. In order to prove the suitability of the coatings for the application in brazing furnaces, the wettability of the coating surfaces by a Ni-based brazing alloy was investigated. The results showed that both mullite and YSZ could be deposited on CFC substrates with a bond coat of W or SiC. Both coatings exhibited good thermal shock behaviour and an excellent non-wetting behaviour against the used Ni-based braze alloy.