【作者】 陈强；

【导师】 毛卫国；

【作者基本信息】 湘潭大学 ， 材料物理与化学， 2010， 硕士

【摘要】 热障涂层（Thermal Barrier Coatings,简称TBCs）具有抗高温氧化和腐蚀的能力,可以有效地降低高温耐热合金基底的使用温度,延长高温部件的使用寿命,从而被广泛应用于航空、航天和大型火力发电等领域。然而,陶瓷涂层内裂纹的萌生、扩展甚至涂层过早的剥落是导致热障涂层失效的重要原因,这一直是研究人员关注的重点问题。在1000°C的热循环条件下,本文首先研究了热障涂层部分材料参数随热氧化时间的变化规律,然后在考虑其演变的影响下,测试分析了热障涂层系统断裂韧性和残余应力的变化规律。主要研究内容如下:第一,用纳米压痕法研究了8wt.% Y₂O₃部分稳定的ZrO₂（8YSZ）热障涂层杨氏模量和硬度随热循环次数增加的演变关系。研究发现:由于受到高温烧结作用的影响,热障涂层的杨氏模量和硬度随热循环次数的不同而出现不同程度的的增长,主要分为两个阶段,当在100次热循环之前,两者随热循环次数的增加而快速增大。当热循环次数超过100次之后,两者随热循环次数的增加而逐渐趋于平缓,甚至保持稳定。热障涂层的杨氏模量和硬度具有明显的各向异性。在测试中,由于陶瓷材料是典型的脆性材料,其压痕测试的实验数据具有一定的分散性。本文采用Weibull分布统计分析方法进行处理,获得了比较满意的结果。第二,用Vickers压痕的方法研究了8YSZ热障涂层系统的断裂韧性。分别采用基于半硬币状裂纹系统的传统压痕断裂力学模型和考虑残余应力影响的Lawn-Evans-Marshall（简称LEM）压痕断裂力学模型来分析维氏压痕实验数据。研究表明,在98N的压制载荷下,用传统模型分析得到的热循环条件下热障涂层表面断裂韧性从1.19MPa·m^1/2变化到4.4MPa·m^1/2;其界面断裂韧性从0.54MPa·m^1/2变化到2.8MPa·m^1/2。在不同的压制载荷下,用LEM模型分析计算得到的热障涂层表面断裂韧性从0.52MPa·m^1/2变化到3.06MPa·m^1/2,相应的表面残余应力从-41MPa变化到-268MPa。热障涂层系统的断裂韧性也呈现出各向异性,且表面断裂韧性整体比界面断裂韧性值要大。第三,通过制备长方形的8YSZ陶瓷棒样品,采用微拉曼光谱法标定了8YSZ材料的压电光谱系数（Piezo-spectroscopic Coefficient,简称PSC）随热循环变化的演变关系。结果表明,PSC随热循环次数增加呈现出指数衰减的趋势,且与杨氏模量的变化趋势相反。第四,研究了热障涂层杨氏模量的变化对X射线衍射法（XRD）测试其残余应力的影响。实验结果表明,在考虑杨氏模量变化的条件下所测得的结果比未考虑其演变情况下的测试结果更加准确。利用PSC的演变规律,本文用微拉曼光谱法测试了热障涂层残余应力随热循环次数的演变关系,其结果与XRD的测试结果具有很好的一致性。在本文中,我们研究了8YSZ热障涂层系统相关力学性能及残余应力场随热循环次数的变化规律,这些结果对评价热障涂层的可靠性具有重要的参考价值。更多还原

【Abstract】 Thermal barrier coatings (TBCs) have been wide applied in stationary turbines of power plants and aircraft turbines to protect basic advanced superalloys materials from high temperature and corrosion, and thereby prolong the lives of these components. However, the crack nucleation, propagation and spallation of ceramic coating greatly limit the application and durability of TBCs in service. In this paper, the change characteristics of partial material properties (e.g. Young’s modulus, hardenss and PSC) of 8YSZ with thermal cycles were studied by nanoindentation method and Raman spectroscopy. And then the fracture toughness and residual stress of TBCs were measured. The related conclusions are summarized as follows:Firstly, the Young’s modulus and hardness in the top coat of 8 wt.% Y2O3-stabilized ZrO2 (8YSZ) TBCs have been measured by nano-indentation. The evolution of Young’s modulus and hardness exhibits two regimes of stiffening in the increasing stage: an initially rapid rise, followed by a more progressive increase due to the sintering effect. And the results also indicate that the Young’s modulus and hardness are anisotropic. The Weibull analysis has been applied to solve the scatter of experimental data due to the brittle characteristic of the ceramic coating.Secondly, the fracture toughness of 8YSZ TBCs is evaluated by Vickers indentation method. Two fracture mechanics theoretical models based on the half-penny crack system were used to analysis the experimental data, respectively. One is the traditional fracture mechanics theoretical model, and the other is the Lawn-Evans-Marshall (LEM) fracture mechanics theoretical model which has considered the influence of residual stress in the coating. The results by the traditional fracture mechanics theoretical model indicate that the surface fracture toughness of ceramic coating changes from 1.19MPa·m1/2to 4.4MPa·m1/2. And the interface fracture toughness of the coating varies from 0.54MPa·m1/2to 2.8MPa·m1/2 with thermal cycles under the load of 98N. However, the results by the LEM fracture mechanics theoretical model show that, the surface fracture toughness of ceramic coating changes from 0.52MPa·m1/2to 3.06MPa·m1/2 with thermal cycles with different indent loads. The corresponding surface residual stress varies -41MPa to -268MPa. The fracture toughness also presents anisotropic. It is found that the value of fracture toughness on the coating surface are generally large than that near the interface location.Thirdly, the evolution of Piezo-spectroscopic Coefficients (PSCs) of freestanding 8YSZ specimens with thermal cycles has been calibrated by Raman spectroscopy. It is shown that the PSC of 8YSZ is an exponential function of thermal cycle N for a given thermal cycling process, and it is opposite to the evolution of Young’s modulus of 8YSZ with thermal cycles. Fourth, the effect of Young’s modulus evolution of 8YSZ on residual stress measurement by X-ray diffraction (XRD) has been studied. When the evolution of Young’s modulus of 8YSZ material is considered, the residual stress derived from the XRD data is more accurate. With the PSCs evolution above, the actual residual stress of 8YSZ TBCs has been determined by the Raman spectroscopy method. The results consist well with that obtained by the XRD.In general, the evolutions of mechanical properties and residual stress of 8YSZ TBCs with thermal cycles have been studied. The results would be useful in evaluating the reliability and life of the 8YSZ TBCs in future.更多还原