【作者】 刘奇星；

【导师】 周益春；

【作者基本信息】 湘潭大学 ， 材料物理与化学， 2012， 博士

【摘要】 热障涂层是一种主要用来起隔热作用的陶瓷涂层,通常有着比较低的导热系数,一般制备在高温金属或合金的表面,可以大幅降低被保护基底的温度,使得合金基底能使用在更高的温度条件下,从而可以提高机器的热效率并延长其寿命。热障涂层的应用非常广泛,如航空航天飞行器的热端部件、化学化工行业、冶金工业以及能源工业等诸多领域。在实际的应用过程中,热障涂层系统的结构与使用环境往往都非常复杂,使得热障涂层系统在服役过程中的应力演化与寿命预测成为热障涂层相关研究工作的重点与难点问题。因此本文研究工作的重点是分析和预测热障涂层涡轮叶片系统在热循环过程中的应力演化及其关键的影响因素,探索热障涂层寿命预测的理论与实验方法。本论文的主要研究内容如下：第一,本文首先基于Fourier热传导定律和有限元方法,分别得到了四层平板模型的热障涂层系统的稳态温度分布及其隔热效果。结果表明TBC承受了主要的温度梯度,TGO、BC、基底各层内温度梯度较小。本文模拟了陶瓷层厚度对热障涂层系统稳态温度的分布的影响,发现TBC越厚,在服役过程中基底表面的温度就越低,热障涂层系统的隔热效果越好。但TBC的厚度增加到一定的程度后,再增加TBC的厚度时,其隔热效果的增加是非常有限的。本文还考察了孔隙率对热障涂层的热传导系数的影响,发现孔隙率对热障涂层的等效热传导系数有较大的影响,孔隙率越高,陶瓷层的热传导系数就越小,其隔热效果也就越好,本文拟合得到等效热传导系数与孔隙率的关系式。第二,本文对四层平板模型热障涂层系统在制备过程中形成的残余应力进行了有限元模拟计算。当平板模型热障涂层系统从制备温度均匀冷却到室温后,各层均存在不均匀的残余应力,制备温度越高,TBC、TGO等层内的初始残余应力越大。TGO内的残余压缩应力特别大,是导致热障涂层系统破坏的主要原因之一；通过模拟计算发现,随着TBC层厚度的增加,TBC、TGO内的残余应力都有着逐渐减小的趋势。本文还对四层平板模型热障涂层系统在热循环过程中力学行为进行了有限元模拟,得到了系统各层应力分布及演化的规律,结果与解析结果符合得较好。第三,本文提出了一种适用于热障涂层涡轮叶片系统的有限元建模方法,基于有限元软件与三维建模软件,可以有效建立热障涂层涡轮叶片系统的有限元分析模型；本文还提出了两种热障涂层涡轮叶片应力演化及危险区域的预测方法,能大大降低有限元分析前处理的成本和人工操作的出错率,提高了预测结果的准确性；本文还编制了一个大数目热循环条件下热障涂层有限元分析的辅助软件,使得热障涂层涡轮叶片系统在大数目热循环的服役条件下的有限元模拟变得比较易于实现、方便快捷。第四,本文对热障涂层涡轮叶片系统在服役过程的应力场进行了有限元模拟,得到了系统在热循环过程中各层的三维温度场、位移场、应力应变的演化等结果,同时基于第一强度理论对陶瓷层内危险区域的分布,即对涂层内可能最先发生破坏的区域进行了分析与预测；本文还模拟了工作温度对热障涂层涡轮叶片系统应力分布及演化的影响,并对热障涂层涡轮叶片系统的寿命进行了初步的探讨。最后,我们还对热障涂层涡轮叶片系统进行了实验研究,实际测量到了系统的温度场、应变场及失效位置的分布,并把实验的结果与有限元的结果进了比较,从而对有限元模拟计算结果的可靠性进行了验证。总之,本论文主要基于有限元方法与实验方法,对热障涂层涡轮叶片系统在服役过程中的温度场、应力场等关键参量进行了有限元模拟与实验测量,得到一些比较有意义的结果,为热障涂层系统的优化设计以及相关制备参数的优化提供了一些参考,同时也拓宽了有限元方法的应用。更多还原

【Abstract】 Thermal barrier coatings is usally a kind of ceramic materials, which with verylow thermal conductivity and excellent high temperature oxidation resistance, whichis deposited on the surface of high temperature resistant metal or superalloy.Thermal barrier coatings can reduce the work temperature of the protected superalloy substrate and reduce the thermal shock effectively. Furthermore, it canalleviate the cooling air and significantly improve the thermal efficiency of themachine. So thermal barrier coatings has been used in the fields of the hotsection ofearonaoutic and astronaoutics, chemistry and chemical engineering, metallurgyindustry and energy industry. Because of the complexity of thermal barrier coatingswhich are covered on the surface of turbine blade system, their structures and theseverity of operating conditions make the stress evolution and life prediction of thesystem in service process is a key and difficult issue. So the main aim of this thesisis to simulate and predict the stress field evolution and the key factors in TBCScovered turbine blade system during thermal cycles, to explore thermal barriercoating life prediction theory and experiment method. The main contents and theonnovations of this thesis are listed as follows,First, this paper based on Fourier law of heat transfer and the finite elementmethod, got the steady temperature distribution and heat insulation effects of thefour hot flat model of the system under different TBC surface temperature. The resultsshow that the TBC layer bear the main temperature gradient, the temperature gradientin TGO BC Substrate is small. This paper simulated the influence of coatingthickness on the temperature distribution, found that the TBC is thicker, thetemperature of the substrate in service process is lower, the heat insulation of the TBCis better. But the TBC thickness increased to a certain degree, the increase ofinsulation effect with the increase of the TBC thickness is very limited. This paperexamined the influence of the porosity on heat transfer coefficient of TBC, found thatthe porosity have a major influence on heat transfer coefficient of TBC. The porosityis higher, the heat transfer coefficient of TBC is smaller, the heat insulation of theTBC is better. The paper also fit the equation between equivalent heat transfercoefficient and the porosity.Secondly, this paper simulated initial residual stress field of the TBC system. When the thermal barrier coating system with flat plate sturcture cooling frompreparation temperature to room temperature, there are uneven residual stress in them,the preparation temperature is higher, initial residual stress in the system is bigger.Residual compression stress in TGO especially large. This layer exist stresssingularity which is one of the main reasons cause thermal barrier coating failure.Through the simulation found that the residual stress in TBC, TGO appear the trend toreduce along with the increase of ceramic powder coating thickness; the thickness ofthe TGO produce in the fabrication process is not obviously affect the stressdistribution in TBC and TGO. In the presence of a temperature gradient conditions tocooling, the change of initial residual stress distribution and ideology in the systemclosely related to the preparation temperature.Third, this paper puts forward a kind of finite element modeling methodapplicable to thermal barrier coating turbine blade system, which can be effective inestablishing the system for finite element analysis model, based on finite elementsoftware and3D modeling software; This paper also puts forward two kinds ofthermal barrier coating turbine blade stress evolution and dangerous area forecastmethod, which can reduce the pre-treatment cost and artificial processing error rateand improve the accuracy of the prediction results; This paper also creates a largenumber of support software with thermal barrier coating of the finite elementanalysis under thermal cycle conditions, which not only make the turbine bladesthermal barrier coating in the large number of thermal cycle work under thecondition of the finite element analysis quick and easy to realize.Fourth, in this paper, the thermal barrier coating turbine blade system in theprocess of stress fields are simulated, so we can obtain some relative results such asthe system in the process of thermal cycle about each layer of the3d temperaturefield, the displacement field and the evolution of stress and strain, and we canascertain the distribution of the danger area in the ceramic layer based on the firststrength theory, which is predicted the most likely happened first damage area. Thispaper also work to simulate the influence of working temperature to thermal barriercoating turbine blade system stress distribution and evolution, and discusses thethermal barrier coating the life of turbine blade system. Finally, we also investigatethe thermal barrier coating of turbine blade system. Through compared the results ofthe finite element with the experimental results, such as the actual measured thesystem of the temperature field, the strain field and the failure of the position, which further verified the finite element simulation of the accuracy of the results.In general, the thesis is based on the finite element experimental method. In theessay, we simulate the critical physical quantities of the thermal barrier coatings inthe service process, provide important reference for the designing of turbine bladesand the optimization of fabricating parameters of the thermal barrier coatings, andalso expand the application scope of the finite element method.更多还原