热障涂层界面微区域热蠕变应力演化分析

热障涂层热循环载荷下不同界面层蠕变特性是影响界面微区域残余应力变化的关键因素,探究热障涂层蠕变与残余应力的关系有助于提高热障涂层的稳定性。以热弹塑蠕变理论为依据,采用Norton蠕变模型,建立陶瓷层、氧化层、粘接层和基体四层几何分析模型,考虑不同层蠕变和蠕变程度因素,研究热循环载荷作用下涂层界面微区域应力演化规律。结果表明,蠕变参数和蠕变层数的变化影响热障涂层界面残余应力的大小和分布,这对预测热障涂层失效具有指导意义。     

等离子喷涂层接触疲劳失效模式及失效机理的研究

研究了等离子喷涂层在不同应力水平下的接触疲劳失效模式与声发射幅值的对应关系,并分析了涂层的接触疲劳失效机理.结果表明:声发射幅值与接触应力的大小无明显的关系,根据疲劳失效时的声发射幅值可以判断涂层接触疲劳失效模式,幅值为87～93 dB时易发生剥落或分层失效,幅值为78～83 dB易发生点蚀失效.涂层表面微凸体与轴承球滚压接触产生黏着磨损以及涂层、磨粒、轴承球三者形成的三体磨料磨损是点蚀失效产生的主要原因.剥落失效主要与涂层表面微观缺陷处裂纹的萌生、扩展以及表面磨损行为有关.层内分层失效是由涂层内部最大剪切应力控制的,而界面分层失效主要是由涂层与基体的低结合强度、热失配以及界面剪切应力造成的.     

热障涂层力学性能的实验测试方法研究进展

涂层-基体体系作为高温热障防护结构被广泛应用于航空、航天、核反应堆等涡轮发动机叶片上, 主要作用是抵抗高温燃气, 保护基体材料. 在服役过程中, 涂层过早出现开裂、脱粘等失效行为直接影响发动机的安全性和可靠性. 长期以来, 热障涂层力学性能的实验测试方法是国内外研究者关注的重点. 首先分析了导致热障涂层失效的失配应力的来源, 重点介绍了热障涂层力学性能研究的实验测试方法、仪器和针对界面脱粘检测的红外热像技术, 接着概述了热障涂层寿命预测方法, 最后分析当前研究中存在的问题, 并对未来的发展的一些方向和有待于进一步研究的问题作了总结.     

热障涂层层裂断裂性能的研究

热障涂层在高温工作环境下,由于热梯度产生的热应力不匹配会导致热障涂层层裂或剥落失效.本文针对热障涂层层裂问题,考虑温度梯度引起的热应力不匹配因素,建立热障涂层层裂I/II复合型断裂准则,并针对分层裂纹在陶瓷层与粘结层界面上和附近的三种存在形式,进行了热障涂层结构单裂纹层裂的算例分析.结果表明界面处层裂纹对应变能释放率影响最大.     

纤维增强陶瓷基复合材料疲劳迟滞回线模型研究

纤维增强陶瓷基复合材料初始加载到疲劳峰值应力时, 基体出现裂纹, 纤维/基体界面发生脱粘. 在疲劳载荷作用下, 纤维相对基体在界面脱粘区往复滑移使得陶瓷基复合材料出现疲劳迟滞现象. 建立了纤维陶瓷基复合材料疲劳迟滞回线细观力学模型, 采用断裂力学方法确定了初始加载纤维/基体界面脱粘长度、卸载界面反向滑移长度与重新加载新界面滑移长度, 分析了4种不同界面滑移情况的疲劳迟滞回线. 假设正交铺设与编织陶瓷基复合材料疲劳迟滞回线主要受0°铺层、轴向纱线内纤维/基体界面滑移的影响, 预测了单向、正交铺设与编织陶瓷基复合材料在不同峰值应力与不同循环的疲劳迟滞回线, 与试验结果吻合.      

INVESTIGATION ON FATIGUE HYSTERESIS LOOPS MODELS OF FIBRE-REINFORCED CERAMIC-MATRIX COMPOSITES

纤维增强陶瓷基复合材料初始加载到疲劳峰值应力时, 基体出现裂纹, 纤维/基体界面发生脱粘. 在疲劳载荷作用下, 纤维相对基体在界面脱粘区往复滑移使得陶瓷基复合材料出现疲劳迟滞现象. 建立了纤维陶瓷基复合材料疲劳迟滞回线细观力学模型, 采用断裂力学方法确定了初始加载纤维/基体界面脱粘长度、卸载界面反向滑移长度与重新加载新界面滑移长度, 分析了4种不同界面滑移情况的疲劳迟滞回线. 假设正交铺设与编织陶瓷基复合材料疲劳迟滞回线主要受0°铺层、轴向纱线内纤维/基体界面滑移的影响, 预测了单向、正交铺设与编织陶瓷基复合材料在不同峰值应力与不同循环的疲劳迟滞回线, 与试验结果吻合.     

基于圆筒模型的热障涂层安定分析

热载荷作用下,由于热障涂层(thermal barrier coatings, TBCs) 各层材料的热不匹配以及材料参数的温度相关等因素,会使热障涂层界面区域存在复杂的应力应变场,影响系统安定性,并导致涂层开裂和剥落. 将热障涂层外凸和内凹微观界面结构简化为多层圆筒模型,借助经典机动安定定理,利用特雷斯卡(Tresca) 屈服准则和增量破坏准则处理对时间的积分问题,避免了常规安定性分析的数学规划问题,建立了热障涂层安定极限分析方法,将材料屈服强度随温度变化关系简化为双线性关系,利用补偿变换的方法简化求解过程,对典型热障涂层安定性进行了研究. 结果表明,利用基于圆筒的安定极限分析方法,能够方便求解安定极限,便于工程应用;热障涂层安定极限值明显高于弹性设计值,且界面外凸区域安定极限高于内凹区域极限值,结构首先在内凹处失效;圆筒模型基体曲率和涂层厚度越大,结构安定极限越高,分析结果与试验结果一致;所建立的热障涂层安定分析方法,对进一步研究考虑蠕变因素影响的热障涂层安定性具有重要意义.      

石墨烯/碳纳米管增强氧化铝陶瓷涂层的制备及摩擦学性能的研究

对碳纳米管进行混杂功能化处理,并与石墨烯,氧化铝按一定配比制成骨料,与胶黏剂混合充分,采用手工涂覆,低温固化的方法在304不锈钢表面制备复合陶瓷涂层.对混杂碳纳米管分子组成进行了表征;对涂层的微观结构,石墨烯和碳纳米管的分散性,涂层的显微硬度、断裂韧性、涂层与基体的结合强度及摩擦学性能进行了分析.结果表明:混杂处理的碳纳米管表面既接枝了活性基团同时也包覆了表面活性剂,复合涂层结构致密,石墨烯和混杂处理的碳纳米管均匀分散在涂层中,且复合涂层的硬度、断裂韧性、结合强度和耐磨减摩性能明显提高.     

工作电压对N36锆合金表面微弧氧化涂层磨蚀性能的影响

通过微弧氧化(MAO)设备在锆(Zr)合金表面制备氧化陶瓷涂层. 研究工作电压对Zr合金表面MAO涂层形貌、硬度、粗糙度、元素分布和相结构的影响. 分析工作电压对Zr合金表面MAO涂层腐蚀和磨蚀性能的影响. 结果表明:MAO涂层表面具有典型的多孔和火山熔融特征,主要由m-ZrO₂和t-ZrO₂相组成. MAO涂层的粗糙度比基体高,且在电压为340 V时的粗糙度最高,达到1.36 μm. MAO涂层可分为内层致密层和外层多孔层,涂层厚度随着工作电压的增加而增加,厚度为5~9 μm. 电压为260 V的MAO涂层的结合强度最高,达到44.3 N. MAO涂层相比较于基体具有更好的耐腐蚀性能,电压为260 V的MAO涂层具有最高的自腐蚀电位(?0.205 V)和最低的腐蚀电流密度(6.24×10?9 A/cm2). 这是因为电压为260 V的MAO涂层具有最致密的结构,而内层致密层可以阻碍腐蚀液进入基体. MAO涂层的主要磨损机理为磨粒磨损和氧化磨损. 工作电压为260 V的MAO涂层的磨损率仅为Zr合金基体的1/4.      

热障涂层氧化残余应力大小与演化过程测试

热障涂层是一种应用广泛的提高高温部件工作效率的技术,在通常的涂层中,粘结层起到过渡和保护基体氧化的作用,在高温环境下,粘结层会发生氧化,而氧化产生的残余应力将引起热障涂层的损伤,表现为涂层的屈曲、起裂和剥落,导致热障涂层失效。研究测试和检测涂层的残余应力,对于评估涂层的安全性和寿命是非常重要的。本文用应力引起光学频谱位移的方法测试了空气等离子喷涂热障涂层中残余应力的大小及分布,并测试了残余应力的大小随氧化时间的演化过程。     

An analytical model of rumpling in thermal barrier coatings

Multilayer thermal barrier coatings (TBCs) deposited on superalloy turbine blades provide protection from combustion temperatures in excess of 1500 °C. One of the dominant failure modes comprises cracking from undulation growth, or rumpling, of the highly compressed oxide layer that grows between the ceramic top coat and the intermetallic bond coat. In this paper, a mechanistic model providing an analytical approximation of undulation growth is presented for realistic cyclic thermal histories. Thickening, lateral growth straining and high temperature yielding of the oxide layer are taken into account. Undulation growth in TBC systems is highly nonlinear and characterized by more than 20 material and geometric parameters, highlighting the importance of a robust yet computationally efficient model. At temperatures above 600 °C, the bond coat creeps. Thermal expansion mismatch occurs between the superalloy substrate and the oxide layer and, in some systems, the bond coat. In addition, some bond coats, such as PtNiAl, exhibit a martensitic phase transformation accompanied by nearly a 1% linear expansion, giving rise to a large effective mismatch. These two mismatches promote undulation growth. Nonlinear interaction between the stress in the bond coat induced by the constraining effect of the thick substrate and normal tractions applied at the surface of the bond coat by the compressed, undulating oxide layer produces an increment of undulation growth during each thermal cycle, before the stress decays by creep. A series of problems for systems without the ceramic top coat are used to elucidate the mechanics of undulation growth and to replicate trends observed in a series of experiments and in prior finite-element simulations. The model is employed to study for the first time the effect on undulation growth of a shift in the temperature range over which the transformation occurs, as well as the relative importance of the transformation compared to thermal expansion mismatch. The role of the top coat and other viable ways of reducing undulation growth are considered.     

Strain Engineering for the Kapitza Resistance of the ZrO2/α-Al2O3 and YSZ/α-Al2O3 Interfaces

The Kapitza resistance is of fundamental importance for the thermal stability of the interface between the ceramic top coat and the thermal growth oxide layer i...     

Parametric studies of failure mechanisms in elastic EB-PVD thermal barrier coatings using FEM

Catastrophic failure of thermal barrier coatings (TBCs), usually occurs due to large scale buckling and spallation, primarily originating at the bond coat and TGO interface. Spallation in TBCs is preceded by a competition between buckling and interface delamination that is stimulated by the waviness of the interface. In the presence of thermal loading, the waviness is responsible for growth of interfacial delamination. In this paper, a finite element model of the two and three layer TBC’s is developed in the commercial code ANSYS to investigate the buckle and interface delamination mechanisms and develop a simplified parametric understanding of these mechanisms. The models for simulation are validated with analytical and experimental results. Parametric relations, in terms of geometric and material parameters representing constituents of the TBC, are developed in this paper for critical stresses and energies causing buckling and debonding initiated instabilities. Through these relations, critical parameters that control failure mechanics are identified for a fail-safe design space.     

三体介质温成形界面接触换热特性的试验研究

温成形摩擦界面模具与工件之间的传热特性对工件质量和模具寿命有重要影响,固体粉末介质导入该摩擦副可实现高温润滑,但其传热特性与传统加工方式的有很大不同.采用稳态法自行设计了三体界面的传热特性试验,研究和分析了界面温度、接触载荷、层厚对带有石墨粉和氧化铝粉润滑层的H62铜合金和45钢之间的三体界面接触换热系数的影响.结果表明:带有石墨粉润滑层的三体界面接触换热系数随温度的增加先升高后降低,随载荷和层厚的增加先缓慢增加后迅速增加;带有氧化铝粉润滑层的三体界面接触换热系数随温度的变化缓慢升高,与载荷基本成线性关系,随层厚的增加而降低.温度改变了固体润滑剂的材料热阻和上下试样表面硬度及氧化层厚度,载荷改变了三体界面实际接触面积和接触属性,层厚决定能否完全隔开上下试样,不同物性固体润滑剂决定了其材料热阻在三体界面接触热阻中的主次关系.     

重型燃气轮机高温透平叶片热障涂层系统中的应力和裂纹问题研究进展

燃气轮机是清洁高效火电能源系统的核心动力装备之一,是关乎国家能源安全和国防安全的战略高技术,是国家重大装备制造水平的标志,被誉为制造业王冠上的明珠。透平前燃气温度代表了燃气轮机的技术水平,人们一直在不断地追求燃气温度的提高。目前,国际最先进的重型燃气轮机的透平前燃气温度已达1600?C,未来还将向1700?C及以上发展。这种极端高温服役环境对高温透平叶片的设计和制造提出了严峻挑战,热障涂层（TBC）技术是解决这一问题的核心技术之一,在燃气轮机发展进程中发挥了重要作用,它不仅具有热障效果,而且还能防止氧化、腐蚀、外来物冲蚀等对叶片造成的损伤。因此,深入研究TBC的失效机理及其影响因素,对TBC的设计、制备及强度评价具有重要意义,对燃气轮机的安全服役具有重要作用。本文拟介绍重型燃气轮机高温透平叶片TBC系统中应力和裂纹问题的国内外最新研究进展,涉及理论、实验和数值分析几个方面。主要内容包括：TBC制备过程中的热应力,热生长氧化物（TGO）及其诱发的生长应力,TBC中的表面裂纹、界面裂纹及表界面裂纹间的竞争,TBC双轴强度评价方法,先进层级TBC中的表面和界面裂纹及其竞争,表面环境沉积物（CMAS）渗入诱发的涂层脱粘行为,陶瓷层烧结及其对TBC开裂的影响等。     

Microstructural and mechanical properties of thermal barrier coating at 1400°C treatment

The mechanical properties of plasma-sprayed thermal barrier coating (TBC) play a vital role in governing their lifetime and performance. This work investigated the microstructural and mechanical properties of TBC with high temperature treatment at 1400°C by scanning electron microscopy and indentation. We calculated elastic modulus and hardness through the application of Weibull statistics analysis. The results indicate that the microstructure of ceramic coating will change continuously at high temperature, and accordingly the porosity decreases due to the grain growths and crack closes. In addition, the elastic modulus and hardness nonlinearly go up with the heat treatment time and go down with increasing porosity. This demonstrates that the microstructural evolution and porosity of TBC are caused by high temperature treatment, and as a result its mechanical properties are influenced.     

A chemo-thermo-mechanically coupled theory for elastic-viscoplastic deformation, diffusion, and volumetric swelling due to a chemical reaction

Thermal barrier coatings (TBCs) are applied to superalloy turbine blades to provide thermal insulation and oxidation protection. A TBC consists of an oxide/metal bilayer: the outer oxide layer (top-coat) imparts thermal insulation, while the metallic layer (bond-coat) affords oxidation protection through the formation of a thermally-grown-oxide (TGO) at elevated temperatures. The TGO layer possesses significantly different elastic, thermal expansion, and creep properties than the surrounding top-coat and bond-coat layers. An intrinsic mechanism which controls the long-term stability and mechanical integrity of a TBC is the volumetric change accompanying the oxide formation, and the attendant locally large stresses that can arise due to the geometrically uneven development of the TGO layer. In this paper we focus on modeling the response of the bond-coat material and its oxidation, and present a new continuum-level thermodynamically-consistent, large-deformation, fully three-dimensional theory which couples high-temperature elastic-viscoplastic deformation of the material with diffusion of oxygen, eventually leading to an oxidation reaction in which the reaction-product causes permanent swelling.The theory is chemo-thermo-mechanically coupled and complex, and at this point in time the list of material parameters appearing in the theory are not fully known. Once the material parameters in our theory are calibrated from suitable experiments, and the theory is numerically-implemented and validated, then the numerical simulation capability should provide an important ingredient for analyzing the evolution of the local stress and strain states which are important ingredients for the life-prediction and performance-improvement of TBCs.     

Measurement of coatings' elastic properties by mechanical methods: Part 2. Application to thermal barrier coatings

Elastic properties of a thermal barrier ceramic coating composed of an NiCoCrAIY bond coat and a ZrO₂(Y₂O₃) top coat were measured by a four-point bending rig in the temperature range 20°C–900°C. Different types of specimens (i.e., with bond coat only or with bond coat and top coat, on one side or on both sides) were employed. Test procedures were based on the theory discussed in Part 1 to enhance accuracy and to estimate confidence intervals. In particular, the method employed at high temperature was calibrated at room temperature by comparing the results with those obtained by methods with low sensitivity to layer thicknesses. For the bond coat, Young's modulus was found to be temperature independent up to about 500°C; a decreasing trend was observed above this temperature. For the top coat, a slightly temperature range examined. A possible explanation is given on the basis of phase transformation and the microstructure of the two layers. At room temperature, Poisson's ratio for the bond coat was found to be near 0.3, whereas a near zero value was measured for the top coat.     

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 1100°C was investigated by the microscopic digital image correlation (DIC) and micro-Raman spectroscopy, respectively. The obtained results showed that, as the cycle number of the thermal shock loading increases, the evolution of the residual stress undergoes 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 1100°C, 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.