| 引用本文: | 韦峥,张从杨,刘长波,董会,雒晓涛,邓元,李长久.热障涂层脱粘裂纹缺陷的高温表征方法与演变规律*[J].中国表面工程,2023,36(4):98~106 |
| WEI Zheng,ZHANG Congyang,LIU Changbo,DONG Hui,LUO Xiaotao,DENG Yuan,LI Changjiu.High Temperature Characterization and Evolution of Delamination Crack in Thermal Barrier Coating[J].China Surface Engineering,2023,36(4):98~106 |
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| 摘要: |
| 热障涂层在服役过程中相邻区域脱粘裂纹的扩展合并是造成陶瓷层最终剥落的重要原因，然而缺乏简单有效的无损测试方法。提出利用空腔高热阻在陶瓷层表面局部热积累，形成表面亮斑的特点，通过亮斑反向跟踪脱粘缺陷的新方法。结果表明，在界面处制备水溶性盐斑，继续喷涂陶瓷层后用水浴溶解的方式可在 YSZ 与金属粘结层界面有效预制特定外形与尺寸的人造脱粘裂纹缺陷；预制脱粘裂纹与表面高温亮斑尺寸呈正相关，且近似呈现为比例系数为 1.031 的线性关系，当预制裂纹直径大于 0.4 mm 时，可在涂层表面观测到亮斑，当预制裂纹直径大于 0.7 mm 时，用亮斑尺寸预测裂纹尺寸的相对误差低于 15%；在梯度热冲击循环下，热障涂层随热冲击次数的增加，表面首先出现亮斑，随后亮斑长大、合并，在 2 500 次左右热循环时合并速度加快，最终陶瓷层在亮斑处局部剥落。基于脱粘裂纹对于纵向热流的阻碍作用，提出一种人造脱粘裂纹缺陷的预制方法，并确立一种通过测量表面亮斑尺寸估计内部裂纹尺寸的热障涂层无损测量方法。解决了热障涂层高温缺陷难以实时观测的问题，并进一步研究了其高温演变规律，可为热障涂层的寿命预测提供数据支持。 |
| 关键词: 热障涂层 脱粘裂纹缺陷 梯度热循环 无损观测 裂纹扩展 |
| DOI：10.11933/j.issn.1007?9289.20220926001 |
| 分类号:TG174 |
| 基金项目:国家科技重大专项（2019-VII-0007-0147）；北京航空航天大学杭州创新研究院 2020 年钱江实验室开放基金（2020-Y2-A-004）资助项目 |
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| High Temperature Characterization and Evolution of Delamination Crack in Thermal Barrier Coating |
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WEI Zheng1, ZHANG Congyang1, LIU Changbo2, DONG Hui1, LUO Xiaotao1, DENG Yuan2, LI Changjiu1
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1.State Key Laboratory for Mechanical Behavior of Materials, Xi’ an Jiaotong University, Xi’ an 710049 , China;2.Hangzhou Innovation Institute, Beihang University, Hangzhou 311100 , China
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| Abstract: |
| Air-plasma-sprayed(APS) thermal barrier coatings(TBCs) are widely used for heat insulation in gas turbines. As reported by many studies in this field, the lifetime of as-sprayed coatings is one of the most concerning issues. The failure of the coatings is related to the formation and propagation of internal cracks. Effective nondestructive methods for characterizing and measuring the defects inside the coating may help establish theories for predicting the service life of TBCs, which are in great demand. However, current testing methods for detecting such defects are limited by the specimen and test environment requirements. The thermal resistance of the crack area perpendicular to the coating increases significantly because of the air in the debonding crack after the ceramic layer of the thermal barrier coating is locally delaminated with the metallic bond coat. According to our previous study, high thermal resistance in the vertical direction of the delamination crack area generated an increased local temperature on the corresponding surface of the ceramic layer and formed bright spots. In this study, we propose heating the ceramic layer surface of the thermal barrier coating with a flame and tracking the debonding defects by the bright spots on the coating surface. The experimental procedure is divided into three steps. First, by preparing salt spots on top of the bond coatings using flame spraying(FS) and resolving them in a water bath after spraying the ceramic layer, an effective method for internal defect prefabrication was established. Second, artificial defects between the ceramic and metallic bond coats of different sizes were fabricated through the FS process and observed using thermal imaging equipment to determine the lower limit of the debonding crack size observable based on the bright spot method. Finally, the evolution of the artificial debonding defects in a gradient thermal shock cycle was investigated. The results show that artificial delamination crack defects with specific shapes and sizes can be prefabricated at the interface between the YSZ and metal bonding layer by preparing water-soluble salt spots at the metallic-bond coating interface, flame-spraying through a mask, preparing the ceramic layer, and dissolving the salt spots with water. It was found that the surface bright spot size was linearly and positively correlated to the delamination crack size, with a slope of approximately 1.031. When the diameter of the preformed crack exceeded 0.4 mm, bright spots were observed on the coating surface. When the diameter of the preformed crack exceeded 0.7 mm, the relative error of predicting the crack size based on the bright spot size was less than 15%. Under gradient thermal shock cycling, with an increase in thermal shock time, the surface of the thermal barrier coating with a specific thermal growth oxide layer thickness first appeared as bright spots, and the bright spots grew and merged. After approximately 2 500 thermal cycles, the merging speed increased, and finally, the ceramic layer locally peeled off at the bright spots. Based on the blocking effect of debonding cracks on the longitudinal heat flow, a prefabrication method for artificial debonding crack defects was proposed, and the corresponding relationship between the size of the bright spot on the surface and the size of the internal debonding crack defect was established. Based on the evolution of the size and shape of the bright spots on the surface, the propagation and merging behaviors of the debonding crack were revealed. An effective, nondestructive method for examining the details of internal cracks inside TBCs is established, which can fill the space for nondestructive testing of TBCs and help establish theories regarding TBC lifetimes. |
| Key words: thermal barrier coating delamination crack defect gradient thermal cycle nondestructive observation crack propagation |
