真实微观结构EB-PVD热障涂层冲蚀失效的有限元模拟
发布时间：2018-10-29 19:03
【摘要】：热障涂层(Thermal Barrier Coatings,简称TBCs)的隔热性能优异,能够显著降低发动机的油耗并延长服役寿命,目前已经广泛应用于航空发动机。发动机在工作时,涂层不可避免的会受到粉尘、硬质颗粒的撞击,使得涂层剥落,这一失效方式被称为冲蚀失效。物理气相沉积(Electron Beam-Physical Vapor Deposition,简称EB-PVD)TBCs高温冲蚀的典型特征为塑性区、密实区以及拐弯带,其中拐弯带是最有可能萌生裂纹的位置之一,因此引起了学术界的广泛关注。传统的EB-PVD冲蚀有限元模型都是用平行的规则柱状晶来表示陶瓷层,忽略了陶瓷层的真实形貌和存在的缺陷,因此本文考虑了陶瓷层的真实形貌,建立了真实微观结构EB-PVD冲蚀模型,从拐弯带和应力场等方面分析了简单模型和真实模型的区别。主要研究内容如下:第一:利用CAD软件以及图像处理技术建立了真实微观结构冲蚀有限元模型。确立了陶瓷层的材料模型,由于陶瓷层是多孔的结构,因此选用GTN模型来表示柱状晶,间隙则用低密度的泡沫模型来表示。第二:从应力场、粒子压入深度等方面分析了简单模型和真实微观结构模型的冲蚀差异,结果表明由于两种模型的柱状晶材料均采用理想弹塑性模型,因此两种模型的无量纲粒子最大压入深度和速度随时间的变化是基本相同的;应力场分析表明,几何形貌对碰撞后的应力影响很大,相同条件下真实微观结构模型的应力明显的大于简单模型的,裂纹扩展的粒子临界无量纲动能也小于简单模型的无量纲动能。这些结果表明在模拟涂层的冲蚀失效时,我们有必要将EB-PVD的真实微观形貌考虑进去。第三:拐弯带是EB-PVD热障涂层高温冲蚀的典型特征,本文首先研究了简单模型冲蚀参数对拐弯带形成的影响,模拟发现粒子的初速度越大、半径越大时,拐弯带倾斜的程度越严重;柱状晶的长细比越大,粒子的压入深度越大,拐弯带形成越明显;其次对比分析了简单模型和真实模型拐弯带形成规律,结果表明由于真实模型柱状晶的尺寸不均匀,模型中柱状晶越大,拐弯带越难形成;垂直入射时,简单模型的拐弯带是对称分布的,而真实模型拐弯带分布并不是对称分布的。
[Abstract]:Thermal barrier coating (Thermal Barrier Coatings,) has been widely used in aero-engines due to its excellent thermal insulation performance, which can significantly reduce engine fuel consumption and prolong service life. When the engine is working, the coating will inevitably be hit by dust and hard particles, which makes the coating flake. This failure mode is called erosion failure. The typical characteristics of Electron Beam-Physical Vapor Deposition, (EB-PVD) TBCs high temperature erosion are plastic zone, dense zone and bend zone, among which the bend zone is one of the most likely crack initiation sites. As a result, the academic community has attracted wide attention. The traditional finite element model of EB-PVD erosion is to represent the ceramic layer by parallel regular columnar crystals, ignoring the true morphology and defects of the ceramic layer, so the true morphology of the ceramic layer is considered in this paper. The EB-PVD erosion model of real microstructure is established, and the difference between the simple model and the real model is analyzed in terms of bend zone and stress field. The main research contents are as follows: first, the real microstructure erosion finite element model is established by using CAD software and image processing technology. The material model of the ceramic layer is established. Because the ceramic layer is porous, the GTN model is used to represent the columnar crystal and the gap is expressed by the low-density foam model. Second, the erosion difference between the simple model and the real microstructure model is analyzed in terms of stress field, particle indentation depth and so on. The results show that the ideal elastic-plastic model is used in the columnar materials of the two models. Therefore, the maximum depth and velocity of dimensionless particles in the two models are basically the same as those of time. The results of stress field analysis show that the geometrical morphology has a great influence on the stress after collision, and the stress of the real microstructure model is obviously larger than that of the simple model under the same conditions. The critical dimensionless kinetic energy of the crack propagation is also smaller than that of the simple model. These results indicate that it is necessary to take the true microstructure of EB-PVD into account when simulating the erosion failure of the coating. Third, the bending zone is a typical feature of EB-PVD thermal barrier coating erosion at high temperature. In this paper, the influence of the erosion parameters of the simple model on the formation of the curved zone is studied. The simulation results show that the larger the initial velocity of particles is, the larger the radius is. The degree of inclination in the bend zone is more serious; The larger the slenderness ratio of columnar crystals is, the greater the depth of impingement is, and the more obvious the bend zone is. The results show that the bigger the columnar crystal in the real model is, the more difficult it is to form the corner zone because of the uneven size of the columnar crystal in the real model. When the incidence is perpendicular, the curve distribution of the simple model is symmetrical, but the distribution of the real model is not symmetrical.
【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
[Abstract]:Thermal barrier coating (Thermal Barrier Coatings,) has been widely used in aero-engines due to its excellent thermal insulation performance, which can significantly reduce engine fuel consumption and prolong service life. When the engine is working, the coating will inevitably be hit by dust and hard particles, which makes the coating flake. This failure mode is called erosion failure. The typical characteristics of Electron Beam-Physical Vapor Deposition, (EB-PVD) TBCs high temperature erosion are plastic zone, dense zone and bend zone, among which the bend zone is one of the most likely crack initiation sites. As a result, the academic community has attracted wide attention. The traditional finite element model of EB-PVD erosion is to represent the ceramic layer by parallel regular columnar crystals, ignoring the true morphology and defects of the ceramic layer, so the true morphology of the ceramic layer is considered in this paper. The EB-PVD erosion model of real microstructure is established, and the difference between the simple model and the real model is analyzed in terms of bend zone and stress field. The main research contents are as follows: first, the real microstructure erosion finite element model is established by using CAD software and image processing technology. The material model of the ceramic layer is established. Because the ceramic layer is porous, the GTN model is used to represent the columnar crystal and the gap is expressed by the low-density foam model. Second, the erosion difference between the simple model and the real microstructure model is analyzed in terms of stress field, particle indentation depth and so on. The results show that the ideal elastic-plastic model is used in the columnar materials of the two models. Therefore, the maximum depth and velocity of dimensionless particles in the two models are basically the same as those of time. The results of stress field analysis show that the geometrical morphology has a great influence on the stress after collision, and the stress of the real microstructure model is obviously larger than that of the simple model under the same conditions. The critical dimensionless kinetic energy of the crack propagation is also smaller than that of the simple model. These results indicate that it is necessary to take the true microstructure of EB-PVD into account when simulating the erosion failure of the coating. Third, the bending zone is a typical feature of EB-PVD thermal barrier coating erosion at high temperature. In this paper, the influence of the erosion parameters of the simple model on the formation of the curved zone is studied. The simulation results show that the larger the initial velocity of particles is, the larger the radius is. The degree of inclination in the bend zone is more serious; The larger the slenderness ratio of columnar crystals is, the greater the depth of impingement is, and the more obvious the bend zone is. The results show that the bigger the columnar crystal in the real model is, the more difficult it is to form the corner zone because of the uneven size of the columnar crystal in the real model. When the incidence is perpendicular, the curve distribution of the simple model is symmetrical, but the distribution of the real model is not symmetrical.
【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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2 谢冬柏,王福会;热障涂层研究的历史与现状[J];材料导报;2002年03期
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