热障涂层高温CMAS腐蚀应变场的DIC表征与分析

发布时间：2018-01-15 07:23

  本文关键词：热障涂层高温CMAS腐蚀应变场的DIC表征与分析　出处：《湘潭大学》2016年硕士论文　论文类型：学位论文

  更多相关文章： DIC法 熔融CMAS腐蚀 热障涂层 应变场

【摘要】：热障涂层(TBCs)作为一种关键的隔热防护材料被应用在航空涡轮发动机上,显著降低了合金表面温度,促进了航空事业的进一步发展。然而在航空发动机高推重比的发展趋势下,燃气进口温度的要求不断提高,热障涂层CMAS腐蚀成为服役环境中最危险的失效形式。如何获得热障涂层CMAS腐蚀失效机制的充分理解是今后航空发动机取得任何进展的关键,而应变场的表征可以为CMAS腐蚀机制的理解提供直接的实验依据。由于热障涂层CMAS腐蚀时应变场的表征是在1200°C以上的高温下进行的,传统的测应变方法不再适用。因此本文采用了一种光学非接触式测应变方法,数字图像相关法(DIC)来表征CMAS高温腐蚀热障涂层的应变场,为日后涂层本构关系的建立提供一个数量级的指导。主要研究内容如下:1、利用高压喷枪将特定比例的耐高温无机胶与氧化亚钴的混合物在热障涂层样品截面制作耐高温人工散斑;实验室人工配制与实际火山灰相似成分的CMAS粉末,用研钵不断研磨使得CMAS粉末的粒径分布集中在20μm左右,并用毛笔刷将一定量CMAS粉均匀涂覆在热障涂层样品的表面;将制好随机散斑且涂有CMAS粉末的样品放入DIC设备装置中的恒温电阻炉中,在1250°C下煅烧30 min进行CMAS高温腐蚀热障涂层的实验,随炉冷却;DIC实时监测采集冷却过程中样品截面的数字图像,利用ARAMIS计算分析软件进行后处理,最终得到CMAS腐蚀热障涂层在冷却过程中应变场的演变。2、研究了热障涂层在从1250°C冷却到25°C过程中,有、无CMAS腐蚀时应变场的演变过程。发现涂层在不同CMAS涂覆量腐蚀下,冷却到300-400°C时,陶瓷层与基底的界面处出现了明显的拉应变,涂层开始开裂,临界开裂应变约为-0.7%;无CMAS腐蚀时,冷却到100°C时陶瓷层与基底的界面处开始开裂,临界应变约为-1.6%;当温度降到25°C时,所有样品均已剥落失效。除此之外,研究发现在冷却过程中,CMAS腐蚀不带基底的陶瓷层时应变大小约为-0.5%。3、建立了CMAS高温腐蚀热障涂层应力应变场的理论模型,分析得到应力应变解析解。代入适当的材料参数,计算得到从1250°C冷却到25°C过程中,不同温度下的应力应变值,发现在冷却过程中,应力应变理论值均随温度降的增大在不断增大,无CMAS腐蚀时应力值最大达到了-200MPa,应变最大为-1.7%,有CMAS腐蚀时应力值最大达到了-900MPa,应变最大为-1.5%。并将应变理论计算值与实验结果相对比,最终发现二者变化趋势一致,基本吻合。
[Abstract]:Thermal barrier coating (TBCs), as a key thermal insulation protection material, has been used in aero-turbine engine to reduce the surface temperature of the alloy. It has promoted the further development of aeronautical industry. However, under the development trend of high propulsion and weight ratio of aero-engine, the requirement of gas inlet temperature has been raised continuously. Thermal barrier coating (CMAS) corrosion has become the most dangerous failure form in service environment. How to get a full understanding of the mechanism of thermal barrier coating CMAS corrosion failure is the key to any progress of aero-engine in the future. The characterization of the strain field can provide a direct experimental basis for the understanding of the corrosion mechanism of CMAS. Since the characterization of the strain field of the thermal barrier coating CMAS corrosion is carried out at a high temperature above 1200 掳C. The traditional strain measurement method is no longer applicable, so an optical non-contact strain measurement method, digital image correlation method (CMAS), is used to characterize the strain field of CMAS thermal barrier coatings. It provides an order of magnitude guidance for the establishment of the constitutive relationship of coatings in the future. The main research contents are as follows: 1. The mixture of high temperature resistant inorganic adhesive and cobalt oxide was prepared by high pressure spray gun on the cross section of thermal barrier coating sample. The CMAS powder with similar composition to the actual pozzolanic ash was artificially prepared in laboratory, and the particle size distribution of CMAS powder was concentrated at about 20 渭 m by continuous grinding with a mortar. A certain amount of CMAS powder is evenly coated on the surface of the thermal barrier coating sample with brush brush. A sample of random speckle and coated with CMAS powder is placed in a constant temperature resistance furnace in a DIC device. The CMAS high temperature corrosion thermal barrier coating was calcined at 1250 掳C for 30 min and cooled with furnace. The digital image of the sample section during cooling process was monitored by DIC and the post-processing was carried out by using the software of ARAMIS calculation and analysis. Finally, the evolution of strain field in the cooling process of CMAS corrosion thermal barrier coating was obtained. It was studied that the thermal barrier coating was cooled from 1250 掳C to 25 掳C. It is found that when the coating is cooled to 300-400 掳C under different amount of CMAS coating corrosion, the obvious tensile strain appears at the interface between the ceramic coating and the substrate. The critical cracking strain is about -0.7. In the absence of CMAS corrosion, the interface between the ceramic layer and the substrate begins to crack at 100 掳C, and the critical strain is about -1.6; When the temperature drops to 25 掳C, all the samples have spalling and failure. In addition, it is found that the strain of CMAs is about -0.5.3 when the ceramic layer without substrate is corroded during the cooling process. The theoretical model of stress-strain field of CMAS high temperature corrosion thermal barrier coating is established, and the analytical solution of stress and strain is obtained by analyzing. The process of cooling from 1250 掳C to 25 掳C is calculated by adding appropriate material parameters. The stress-strain values at different temperatures show that the theoretical values of stress-strain increase with the increase of temperature drop in the cooling process, and the maximum stress value reaches -200MPa in the absence of CMAS corrosion. The maximum strain is -1.7, the maximum stress value is -900MPa when there is CMAS corrosion, and the strain maximum is -1.5. The calculated strain theory is compared with the experimental results. Finally, it is found that the change trend of the two is consistent and basically consistent.
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG174.4
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本文编号：1427358