【作者】 毛卫国；

【导师】 周益春；

【作者基本信息】 湘潭大学 ， 材料物理与化学， 2006， 博士

【摘要】 热障涂层(Thermal Barrier Coatings，简称TBCs)是一种陶瓷涂层，具有优良的抗高温氧化和非常低的热传导系数，它通过粘结层沉积在耐高温金属或超合金的表面，可以有效降低被保护基材的服役温度，减轻其热冲击载荷，降低对冷却空气的需求，提高器件的热效率，从而被广泛应用于航空航天、化工、冶金和能源等领域。热障涂层与基底之间的界面结合和破坏问题一直是热障涂层研究工作中的重点研究内容。由于热障涂层系统材料参数的不匹配，陶瓷涂层通常受到压缩应力、拉伸应力和弯曲剪切应力的共同作用，最终与基底相剥离，从而失去保护基底的功能和意义。因此本文研究工作的重点是首先分析和预测了热循环下热障涂层应力场变化，为后面章节分析涂层界面破坏提供了基础；其次是在热力联合作用下对热障涂层界面破坏过程进行了实验和理论分析。本论文主要研究内容如下：第一，本文建立了在等离子体喷涂工艺制备样品后的冷却过程中热障涂层残余应力场的理论模型，得到了一个解析表达式。通过应用等离子体喷涂参数，本文正确预测了在制备后原始样品内的残余应力场。然后在考虑了热循环温度、材料的弹塑性变形和蠕变变形特性、热循环次数和系统弯矩变形等因素的影响下，本文推导了热循环下热障涂层多层系统的本构方程，得到了热循环中热障涂层应力场的解析表达式，并用该解析表达式预测了热障涂层应力场，其结果与文献实验测试结果相符得很好。然后还分析了各层应力场的变化规律、系统残余变形和热循环次数之间的关系。第二，本文分析和讨论了高温热循环条件下热障涂层屈曲失效机制。在考虑温度和载荷效应影响下，本文建立了一阶剪切理论分析模型，利用变分原理和欧拉方程推导出了含涂层界面穿透裂纹的屈曲方程和定解条件；然后采用状态空间法得到了屈曲控制方程及其封闭形式解，分析了热障涂层厚度、界面裂纹长度和位置、系统温度对TBC系统屈曲破坏的影响。计算结果表明：裂纹长度对热障涂层屈曲破坏有至关重要的影响。第三，本文采用等离子体喷涂工艺分别制备了含内埋穿透脱层、表面裂纹等缺陷的实验样品，并利用万能试验机、氧乙炔加热装置、显微观察装置和热电偶测温装置等仪器，对热障涂层的屈曲、弯曲和拉伸破坏机制进行了深入的实验研究。其主要内容有：(1)通过控制加载载荷和温度，本文首次得到了含界面脱层(缺陷)的热障涂层屈曲破坏实验现象和相应的临界破坏条件，同时也充分证实了在应用过程中热障涂层系统确实能发生屈曲破坏。应用Suo-Hutchinson双层理论模型，本文得到了热障涂层界面屈曲破坏的断裂韧性、能量释放率和应力强度因子，并对涂层屈曲破坏机制进行了详细地讨论。(2)对于热力联合作用下热障涂层界面弯曲破坏，本文主要得到了两种不同类型的弯曲破坏模式Ⅰ和Ⅱ，同时对两种弯曲模式进行较为详细的阐述和解释。通过SEM和EDX观察和分析，本文分别建立了两种弯曲模式的破坏过程和机制。然后应用Suo-Hutchinson双层理论模型，本文得到了热障涂层界面弯曲破坏的断裂韧性、能量释放率和应力强度因子。(3)对于热力联合作用下界面拉伸破坏，本文观察了涂层内横向裂纹萌发、形成、扩展和饱和全过程，并记录了涂层表面裂纹数量与拉伸载荷(位移)之间关系。通过扫描电子显微镜和能谱分析，本文确定了各种界面拉伸破坏模式的断裂位置，同时建立了热障涂层界面拉伸破坏机制模型。应用Suo-Hutchinson双层理论模型和剪切滞后理论模型，得到了热力联合作用下热障涂层界面断裂韧性、能量释放率和应力强度因子。总之，本论文的研究工作较为系统地分析了热障涂层界面破坏过程和机制，为今后的热障涂层研究和应用提供重要的实验基础和理论帮助。更多还原

【Abstract】 Thermal Barrier Coating (TBC) is a kind of ceramic layers with excellenthigh temperature oxidation resistance and very low thermal conductivity,which is sprayed onto bond coat (NiCrAlY) deposited on the surface ofsubstrate. TBC can effectively reduce the service temperature of theprotected substrate and alleviate the thermal shock loading. Furthermore, itcan reduce the requirement for cooling air and improve the thermalefficiency of aircraft/engine. So TBC has been widely used in the fields ofspace flight, chemical industry, metallurgy and energy industry.The interface coalescence and spallation problems always are the keysubjects in thermal barrier coating investigations. Due to the mismatch inthe thermo-mechanical parameters of metals and ceramics, the ceramiccoating often detaches from the substrate under the coupled effects ofcompression, shear and tensile stresses, which would result in thedegradation and fracture of substrate. So the emphasis of this thesis is tofirstly analyze and predict the variations of thermal/residual stress fields inthermal barrier ceramic coating system during thermal cycles, which makesa contribution to the interface failure studies of the TBC in the followingsections. And then the experimental and theoretical investigations of theinterface failure mechanism of the TBC were analyzed and performed underthermo-mechanical loadings. The main content in this paper are listed asfollows,Firstly, the modeling of the residual stress fields of the TBC wasestablished and a analytical solution was deduced during cooling to ambientafter air plasma sprayed deposition. The residual stresses in the as-receivedsamples were successfully predicted by the plasma spraying parameters.Furthermore, a new two-dimensional analytical solution of thethermal/residual stress field has been obtained under the condition ofnon-linear coupled effects of temperature gradient, thermal fatigue,deposited residual stress, thermally grown oxide (TGO) thickening,elasto-plasticity deformation and creep deformation of TBC. At the sametime, the influence of bending moment and curvature on thermal/residualstress variations in TBC is also considered during thermal cycling. The calculated results of the stress field of the TBC system, which wereobtained by the above analytical solution, agreed well with the previousexperimental results. The relationships of the stress field evolutions,residual strain in TBC and thermal cycles were also obtained and discussed,which was of particular advantage to research the interface failure of theceramic coating.Secondly, thermal residual stress in TBC may directly cause adhesivefailure (delamination at interface) or cohesive failure (spalling ormicro-cracking within ceramic coating). The buckling delamination failuremechanism of thermal barrier ceramic coating was analyzed and reviewed inits operation condition. Under external thermal and mechanical loadings,the first order shear deformation theory model was introduced to analyzethe thermo-mechanical buckling characteristic of thermal barrier coatings(TBC) system with arbitrary across-the-width delamination. Characteristicequation and boundary conditions are derived on the basis of the potentialvariation principle and Euler equations. The closed-form solutions andequations governing buckling of the TBC system were obtained by the statespace scheme. The effects of the TBC system aspect ratio, relative thickness,delamination location and length, temperature gradient onthermo-mechanical buckling failure of TBC are discussed in detail. It wasfound that the evolution of initial interface delamination length played animportant role in predicting the buckling failure characteristic and itsdurability of the TBC system.Thirdly, in experimental investigations, the special samples with athrough-width delamination or surface crack were designed and prepared byair plasma spraying technique. And then the interface failure investigationsof the TBC system were performed under the different compressive, tensileor shear loading conditions by the combinations of the compressive tests,oxyacetylene torch heating equipment, observation and measurementequipments. The main contents are given in the following, (1) thedelamination buckling failure phenomena and critical buckling loadingconditions were obtained firstly by controlling the external mechanicalloading and temperature, which substantially indicated that thedelamination buckling failure existed in TBC service. The interface fracturetoughness, energy release rate and stress intensity factor were evaluated and calculated by Suo-Hutchinson model. The thermo-mechanical bucklingfailure mechanism of the TBC system was discussed in detail. (2) Twodifferent bending failure modes (ⅠandⅡ) were observed and discussedduring thermo-mechanical bending loading. The bending failuremechanisms of the two modes in TBC system were analyzed by SEM andEDX observations. The interface fracture toughness, energy release rate andstress intensity factor in thermo-mechanical bending tests were alsoevaluated and calculated by Suo-Hutchinson model. (3) The entire processof the initiation, nucleation, propagation and coalescence of the multipletransverse surface cracks in the ceramic coating was clearly observed underthermo-mechanical tensile loadings. The relationship of the transversesurface cracks number and displacement was recorded and discussed indetail. In addition, the fracture location of each interface failure mode wasidentified by SEM and EDX. Finally, the interface fracture toughness,energy release rate and stress intensity factor in tensile tests werecalculated using Suo-Hutchinson model and shear lag model. In general, theinvestigations in this thesis have systematically analyzed the interfacefailure mechanism, which is of great advantage to provide the experimentaland theoretical basis of the TBC system in the future.更多还原