Segmentation crack formation dynamics during air plasma spraying of zirconia
Segmentation crack formation dynamics during air plasma spraying of zirconia
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DOI：
10.1016/j.actamat.2019.10.052
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发表时间：
2020-01
期刊：
影响因子：
9.4
通讯作者：
S. Shinde;E. Gildersleeve V;C. A. Johnson;S. Sampath
中科院分区：
文献类型：
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作者：
S. Shinde;E. Gildersleeve V;C. A. Johnson;S. Sampath
空气等离子喷涂（APS）氧化钇稳定氧化锆（YSZ）热障涂层（TBCs）是燃气涡轮机工业中成熟的技术。传统的APS TBC是具有不均匀分布的缺陷（微裂纹、孔隙等）的层状结构。这使得它与其本体对应物相比同时具有低的导热率和弹性模量。然而，在热循环过程中，界面缺陷可能是分层失效的来源。此外，常规多孔涂层在持续暴露期间可能会发生烧结，这会通过硬化诱导的分层加剧失效。电子束物理气相沉积（EB-PVD）TBC涂层由于其致密的柱状结构而不易于烧结和分层。这导致考虑更经济地应用具有周期性垂直分段裂纹的致密APS热障涂层。这种致密的垂直裂纹涂层（DVC）已经成功地开发并应用于燃气涡轮机发动机中。这些微结构是通过控制高沉积温度的工艺条件原位产生的。然而，这种分段裂纹的机理尚不清楚。在这项研究中，形成动态的分割裂纹观察通过原位梁曲率监测在沉积过程中结合微观结构的评价。观察到涂层的初始层是致密的，没有分段开裂。随着后续层的沉积，周期性宏观裂纹开始并通常通过剩余的涂层厚度传播。分段开裂开始后，涂层的面内应力显著降低。这些结果是一致的，通过解释薄膜断裂文献，并提供了一个初步的框架来解释实验观察。
Air Plasma Sprayed (APS) Yttria Stabilized Zirconia (YSZ) Thermal Barrier Coatings (TBCs) is a well-established technology in the gas turbine industry. A conventional APS TBC is a layered structure with heterogenous distribution of defects (microcracking, pores, etc.) which allow it to simultaneously possess low thermal conductivity and elastic modulus compared to its bulk counterpart. However, interfacial defects can be a source of delamination failure during thermal cycling. In addition, conventional porous coatings can experience sintering during sustained exposure, which augments failure through stiffening-induced delamination. Electron Beam Physical Vapor Deposition (EB-PVD) TBC coatings, due to their dense columnar structures, are less susceptible to both sintering and delamination. This has led to the consideration of more economically-applied APS TBCs that are dense with periodic vertical segmentation cracks. Such dense vertically cracked coatings (DVCs) have been successfully developed and implemented in gas turbine engines. These microstructures are producedin-situthrough control of the process conditions with high deposition temperatures. However, the mechanism of such segmentation cracks is unclear. In this study, formation dynamics of segmentation cracks were observed throughin-situbeam curvature monitoring during deposition in combination with microstructural evaluations. It was observed the initial layers of the coating are dense without segmentation cracking. As subsequent layers are deposited, periodic macrocracking initiates and typically propagates through the remaining coating thickness. Thein-situin-plane coating stress is significantly reduced after segmentation cracking begins. These results are reconciled through interpretation of thin-film fracture literature, and an initial framework to interpret the experimental observations is provided.