Thermal Analysis of Turbine Blades with Thermal Barrier Coatings Using Virtual Wall Thickness Method

Avirtual wall thicknessmethod is developed to simulate the temperature field of turbine bladeswith thermal barrier coatings(TBCs),to simplify the modeling process and improve the calculation efficiency.The results show that the virtualwall thickness method can improve themesh quality by 20%,reduce the number ofmeshes by 76.7%and save the calculation time by 35.5%,compared with the traditional real wall thickness method.The average calculation error of the two methods is between 0.21%and 0.93%.Furthermore,the temperature at the blade leading edge is the highest and the average temperature of the blade pressure surface is higher than that of the suction surface under a certain service condition.The blade surface temperature presents a high temperature at both ends and a low temperature in themiddle height when the temperature of incoming gas is uniformand constant.The thermal insulation effect of TBCs is the worst near the air film hole,and the best at the blade leading edge.According to the calculated temperature field of the substrate-coating system,the highest thermal insulation temperature of the TC layer is 172.01 K,and the thermal insulation proportions of TC,TGO and BC are 93.55%,1.54%and 4.91%,respectively.

A modified single edge V-notched beam method for evaluating surface fracture toughness of thermal barrier coatings

The surface fracture toughness is an important mechanical parameter for studying the failure behavior of air plasma sprayed(APS)thermal barrier coatings(TBCs).As APS TBCs are typical multilayer porous ceramic materials,the direct applications of the traditional single edge notched beam(SENB)method that ignores those typical structural characters may cause errors.To measure the surface fracture toughness more accurately,the effects of multilayer and porous characters on the fracture toughness of APS TBCs should be considered.In this paper,a modified single edge V-notched beam(MSEVNB)method with typical structural characters is developed.According to the finite element analysis(FEA),the geometry factor of the multilayer structure is recalculated.Owing to the narrower V-notches,a more accurate critical fracture stress is obtained.Based on the Griffith energy balance,the reduction of the crack surface caused by micro-defects is corrected.The MSEVNB method can measure the surface fracture toughness more accurately than the SENB method.

Constitutive parameters identification of thermal barrier coatings using the virtual fields method

Thermal barrier coatings (TBCs) are widely applied in thermal components to protect metallic components. Owing to the complex layered structure of TBCs and difficult preparation of coating, the mechanical characterization of TBCs should be of primary importance. With regard to TBCs, this study deals with the constitutive parameters identification of bi-material. Considering the complex construction and boundary of bi material, the virtual fields method (VFM) was employed in this study. A methodology based on the optimized virtual fields method combined with moire interferometry was proposed for the constitutive parameters identification of bi-material. The feasibility of this method is verified using simulated deformation fields of a two-layer material subjected to three point ben ding loading. As an application, the deformation fields of the TBC specimens were measured by moire interferometry. Then, lhe mechanical parameters of the coating were identified by the proposed method. The identification results indicate that Young's modulus of the TBC top coating is 89.91 GPa, and its Poisson's ratio is 0.23.

Review of Numerical Simulation of TGO Growth in Thermal Barrier Coatings

Thermally grown oxide(TGO)is a critical factor for the service life of thermal barrier coatings(TBC).Numerical simulations of the growth process of TGO have become an effective means of comprehensively understanding the progressive damage of the TBC system.At present,technologies of numerical simulation to TGO growth include two categories:coupled chemical-mechanical methods and mechanical equivalent methods.The former is based on the diffusion analysis of oxidizing elements,which can describe the influence of bond coat(BC)consumption and phase transformation in the growth process of TGO on the mechanical behavior of each layer of TBC,and has high accuracy for the thickness evolution of TGO,but they cannot describe the lateral growth of TGO and the rumpling phenomenon induced.The latter focuses on describing the final stress and strain state after the growth of a specific TGO rather than the complete growth processes of TGO.Based on the measured TGO thickness growth curve,simulations of thickening and lateral growth can be achieved by directly applying anisotropic volumetric strain to oxidized elements and switching elements properties from the BC to the TGO.

FEM ANALYSIS OF THERMAL STRESSES IN GRADIENT THERMAL BARRIER COATINGS PRODUCED BY EB-PVD

Gradient thermal barrier coatings (GTBCs) produced by co-deposition of mixtures ofAl-Al2 O3-YSZ onto metallic bond coat exhibited longer lifetimes than the two-layeredTBCs. The finite element method (FEM) numerical models were used to investigatestress and strain states in the GTBCs and traditional two-layered TBCs as they cooledto 750℃ from a stress-free state at 850℃.

Effects of Layer Thickness and Edge Conditions to Thermoelastic Characteristics on Thermal Barrier Coatings

The thermoelastic behaviors of such as temperature distribution, displacements, and stresses in thermal barrier coatings (TBC) are seriously influenced by top coat thickness and edge conditions. The top coat of TBC specimens prepared with TriplexPro?-200 system was controlled by changing the processing parameter and feedstock, showing the various thicknesses and microstructures. A couple of governing partial differential equations were derived based on the thermoelastic theory. Since the governing equations were too involved to solve analytically, a finite volume method was developed to obtain approximations. The thermoelastic behaviors of TBC specimens with the various thicknesses and microstructures were estimated through mathematical approaches with different edge conditions. The results demonstrated that the microstructure and thickness of the top coat, and the edge condition in theoretical analysis were crucial factors to be considered in controlling the thermoelastic characteristics of plasma-sprayed TBCs.

Thermal Shock Property of Al/Ni-ZrO_2 Gradient Thennal Barrier Coatings

Al/Ni-ZrO2 gradient thennal barrier coatings are made on aluminum substrate using plasma spraying method and one direction thermal shock properties of the coatings are studied in this paper. The results show that pores in coatings link to form cracks vertical to coating surface. They go through the whole ZrO2 coating once vertical cracks form. When thermal shock cycles increase, horizontal cracks that result in coatings failure forms in the coatings and interface. And vertical cracks delay appearance of horizontal cracks and enhance thermal shock property of coatings. Failure mechanisms of coating thermal shock are discussed using experiments and finite element method.

Residual stress evolution regularity in thermal barrier coatings under thermal shock loading

Residual stress evolution regularity in thermal barrier ceramic coatings （TBCs） under different cycles of thermal shock loading of 1 100℃ was investi- gated by the microscopic digital image correlation （DIC） and micro-Raman spec- troscopy, respectively. The obtained results showed that, as the cycle number of the thermal shock loading increases, the evolution of the residual stress under- goes three distinct stages： a sharp increase, a gradual change, and a reduction. The extension stress near the TBC surface is fast transformed to compressive one through just one thermal cycle. After different thermal shock cycles with peak temperature of 1 100℃, phase transformation in TBC does not happen, whereas the generation, development, evolution of the thermally grown oxide （TGO） layer and micro-cracks are the main reasons causing the evolution regularity of the residual stress.

热障涂层在航空发动机涡轮叶片上的应用、失效与维护

航空发动机涡轮叶片热障涂层对延长涡轮叶片的使用寿命具有至关重要的作用。首先概述了航空发动机热障涂层的重要性,其次归纳了航空发动机涡轮叶片热障涂层的制备技术及应用特点,主要对大气等离子、电子束物理气相沉积、等离子喷涂-物理气相沉积等3种热障涂层进行了论述。在此基础上,重点阐述了热障涂层在航空发动机涡轮叶片中的典型失效形式,包括高温氧化失效、热腐蚀失效及颗粒物冲击,对以上失效形式的失效机理进行了重点论述。最后结合发动机状态监控及涡轮叶片孔探技术,对涡轮叶片热障涂层的常见典型失效给出了工程案例分析与建议。

Simulation of residual stresses and their effects on thermal barrier coating systems using finite element method

Thermal barrier coating(TBC)systems are widely used in industrial gas-turbine engines.However,premature failures have impaired the use of TBCs and cut down their lifetime,which requires a better understanding of their failure mechanisms.In the present study,experimental studies of isothermal cycling are firstly carried out with the observation and estimation of microstructures.According to the experimental results,a finite element model is established for the analysis of stress perpendicular to the TBC/BC interface.Detailed residual stress distributions in TBC are obtained to reflect the influence of mechanical properties,oxidation,and interfacial roughness.The calculated results show that the maximum tensile stress concentration appears at the peak of TBC and continues to increase with thermal cycles.Because of the microstructural characteristics of plasma-sprayed TBCs,cracks initialize in tensile stress concentration(TSC)regions at the peaks of TBC and propagate along the TBC/BC interface resulting in the spallation of TBC.Also,the inclusion of creep is crucial to failure prediction and is more important than the inclusion of sintering in the simulation.

先进航空发动机高温功能涂层研究进展

航空发动机是飞机的“心脏”。先进航空发动机正在向高推重比、高效率、低油耗和长寿命方向发展。以热障涂层、热/环境障复合涂层、高温隐身涂层等为代表的高温功能涂层应用于航空发动机关键热端部件,起着提升发动机服役性能、服役寿命和安全可靠性的重要作用。本文以热障涂层、热/环境障复合涂层、高温隐身涂层等为例,系统概述了近年来国内外以及北京航空航天大学在高温功能涂层材料设计、涂层制备科学与技术、涂层性能评价表征等方面的研究进展,并展望了先进航空发动机新型高温功能涂层所面临的挑战和发展动向。未来先进高温功能涂层的研究重点将集中在多功能复合涂层、极端环境适应性和工艺适配性等方面。

硅基聚合物耐高温衍生陶瓷涂层制备与应用研究进展

随着航空航天领域的不断发展,金属以及碳材料等高温结构部件的服役条件日益苛刻。通过恰当的工艺在高温结构部件表面制备硅基陶瓷涂层并赋予其特殊性能,可有效提高高温结构部件的使用寿命。近年来,聚合物前驱体转化陶瓷涂层逐渐成为一种无机涂层制备的新方法。该方法具有制备工艺简便、涂层功能拓展性强等特点,得到了研究者越来越多的关注。本文主要综述了硅基聚合物前驱体转化陶瓷涂层的研究进展。首先从聚合物陶瓷涂层的制备展开,简要介绍了硅基聚合物前驱体、填料种类以及涂覆工艺和裂解方式对涂层结构以及性能的影响。随后,重点讨论了聚合物前驱体转化陶瓷涂层在耐高温防护领域,包括抗氧化、环境障、热障涂层的应用进展。最后,指出了聚合物陶瓷涂层在涂层性能提升及缺陷控制等方面的问题,并对其发展方向进行了展望,例如通过在硅基前驱体中引入Hf,Zr,Ta等超高温元素,提高陶瓷涂层的耐温等级,以及发展高效的陶瓷化新技术,从而提高陶瓷转化效率及涂层适用性范围等。

热障涂层服役温度测试与隔热机理

热障涂层(TBC)被用于航空发动机涡轮叶片表面的热防护,主要由粘结层和陶瓷层组成,准确测量陶瓷层表面与粘结层/陶瓷层界面温度分布对指导涂层高隔热结构设计与制备具有重要意义。现有非接触式与接触式测温技术可测量表面温度,接触式测温技术可测量界面温度。主要介绍了3种用于测量航空发动机涡轮叶片表面温度的技术,其中,适用于TBC表面测温的包括以光学原理为主的红外辐射、荧光、晶体、光纤测温技术;以热致变原理为主的示温漆测温技术;适用于TBC界面测温的以热电原理为主的填埋式热电偶、薄膜热电偶测温技术,并介绍了其测温的原理、优势和局限性。进一步对TBC隔热机理及性能优化进行了介绍,并对TBC表/界面测温技术及涂层结构设计方向进行了展望。

热障涂层材料制备技术的研究进展及失效分析

热障涂层具有良好的隔热效果和抗高温氧化性能,应用于航空发动机可以显著提高高温部件的使用温度和寿命。先进航空发动机的发展对热障涂层陶瓷面层材料的防护效果和使用寿命提出了更高的要求。综述了先进航空发动机热障涂层体系的研究进展,对近年来国内外热障涂层的陶瓷层和粘结层材料体系、制备技术进行了详细介绍,对涂层失效进行了分析,展望了下一代高性能航空发动机热障涂层的研究和应用前景。

热分解法合成制备Ti/RuO_(2)-HfO_(2)的工艺优化与电容性能研究

通过热分解法制备Ti/RuO_(2)-HfO_(2)二元复合氧化物涂层,利用XRD对涂层组织结构进行表征,通过循环伏安和充放电曲线分析对涂层的超电容性质进行研究。实验结果表明,Hf的加入有利于非晶态组织的形成;随着Hf含量的增加,电极比电容呈现先增大后减小的变化趋势,当Hf含量为50%时,电极比电容最大;Hf具有促进电化学稳定性的作用。

热障涂层热力耦合条件下的应力仿真计算

有限元模拟是研究热障涂层(thermal barrier coatings,TBCs)界面处热生长氧化层(thermally grown oxides,TGO)应力演变的有效手段之一,可为探索TBCs失效机制提供理论支撑。采用先进的热障涂层多因素耦合设备对热障涂层圆管试样模拟发动机工况进行热力耦合循环实验和热循环实验。利用有限元软件ABAQUS对包含真实初始TGO形貌的热障涂层进行有限元建模,分析实验过程中TGO的应力和变形规律。结果表明:在不考虑TGO及界面开裂的情况下,无论是热力耦合模型还是热循环模型,随着循环次数的增加,Mises应力均增加;加热过程中TGO受拉,冷却过程中TGO受压;加热过程的应力均远小于冷却至室温时的应力。经过相同的循环次数,热力耦合模型中的应力值均高于热循环模型中的应力值。经过20,45,70次热循环后,冷却至室温时,TGO应力分别达到2.85,3.65,3.55 GPa,而经过相同次数的热力耦合循环后,冷却至室温时,相同位置的TGO应力分别达到4.01,5.0,4.81 GPa。与热循环相比,在热力耦合条件下,经过相同循环次数冷却至室温时的TGO应力显著增加。

基于热阻法的多层热障涂层叶片隔热预测模型研究

为实现有热障涂层(TBCs)的叶片表面温度预测,开展基于热阻法的热障涂层隔热理论分析,建立了TBCs隔热理论模型,模型包括有热障涂层叶片表面温度预测式(VT-TBCs)和热障涂层隔热温度预测式(IT-TBCs),并分别基于IT-TBCs和仿真分析了陶瓷层(TC)、粘结层(BC)的厚度、导热系数对隔热温度的影响。结果表明:与数值仿真结果相比,VT-TBCs的计算结果最大误差不超过3%,平均误差为0.65%。通过IT-TBCs分析可知,导热系数小于0.5 W(/m·K)时,热障涂层厚度与隔热温度趋近对数关系,当导热系数大于0.5 W(/m·K)时,热障涂层厚度与隔热温度趋近线性关系,BC层的导热系数与厚度对隔热温度基本无影响。仿真分析结果与IT-TBCs分析结果一致。

热障涂层厚度的脉冲涡流检测反演方法

针对热障涂层厚度的高精度测量,提出一种脉冲涡流检测反演方法。该方法提出两阶段处理技术对脉冲涡流检测信号进行预处理,采用主成分分析法提取预处理信号的主成分分量,最后构建BP神经网络实现涂层厚度预测。通过COMSOL建模仿真实验证明两阶段处理方法可有效地减小提离效应并区分厚度特征的变化,基于主成分分析的特征提取方法能够对陶瓷层和粘结层厚度变化进行分类识别。结果显示该方法对陶瓷层厚度计算的平均相对误差约为0.4%,对粘结层厚度计算的平均相对误差约为2.6%。可见,该方法对热障涂层厚度的反演精度较高。

热障涂层系统热冲击裂纹扩展规律分析

为了深入理解热障涂层材料的热断裂行为,对热障涂层材料热冲击裂纹扩展问题进行了研究。利用瞬态相互作用积分方法提取了热障涂层材料裂纹尖端的瞬态热应力强度因子,同时基于裂纹扩展准则结合材料的断裂韧性和提取的瞬态热应力强度因子,分析了多界面热障涂层材料热冲击裂纹的扩展规律,进一步可以确定热冲击裂纹扩展的重要临界,如预制裂纹的开裂时刻、最终裂纹长度和最终裂纹扩展时间。研究结果表明,方法可以获得热冲击裂纹扩展过程中的重要临界参量,为分析热冲击裂纹扩展规律奠定基础。

不同涂层厚度组合热障涂层系统的热分析

热障涂层具有较低的热导率、较高的熔点和良好的隔热性,能够有效降低金属基体的温度。采用有限元法建立6种不同涂层厚度组合热障涂层系统模型,对比分析陶瓷层、黏结层、基体的温度场与应力场,讨论陶瓷层厚度、黏结层厚度对热障涂层系统的温度场和热应力影响。分析结果显示,在热障涂层系统中,陶瓷层至关重要,能够有效地降低基体的温度,从而延长设备的使用寿命。具体来说,陶瓷层厚度每增加0.1 mm,基体的最高温度可以下降4.6℃。该发现提供了一种优化热障涂层性能的方法,即通过增加陶瓷层的厚度来进一步降低基体的温度。然而,仅仅关注陶瓷层的厚度是不够的。研究还发现,随着陶瓷层厚度的增加,陶瓷层、黏结层和基体的热应力会不断减小。但是,当黏结层的厚度减小时,各部分的热应力会略微增大。这一结果揭示了热障涂层系统中不同组成部分之间的相互作用和平衡关系。