Damage mechanisms of EB-PVD thermal barrier coatings under combined CMAS and erosion loads

热障涂层在航空发动机和固定式燃气轮机中的沉积对热障涂层的损伤越来越受到重视。在较低的工作温度下，腐蚀是另一种重要的损伤现象。该项目的最终目标是不变的：揭示CMAS和颗粒侵蚀的联合损伤，获得底层参数之间的系统关联，并揭示在这种复杂载荷情况下TBCs的损伤机理。因此，本文系统地研究了CMA渗透对EB-PVD热障涂层冲蚀行为的影响。在第一个注资期内，发现7YSZ的显微组织对CMAS的渗透动力学、抗冲蚀性能以及复合损伤有很大的影响。有趣的是，渗透的热障涂层在垂直颗粒撞击下的抗冲蚀性能往往是以牺牲热障涂层的机械完整性为代价的。这也适用于新型抗CMA涂层，如Gd-锆酸盐和Al_2O_3。沉积和热障涂层的化学成分以及在温度梯度下不同的渗透深度决定了热障涂层中反应相的形成和损伤的发展。渗流过程的第一个分析模型、相计算(CALPHAD)和机械性能测量在定性上与改进涂层的保护性能和预测损伤的实验和机会很好地相关。根据第一个资助期的结果，在第二个也是最后一个项目阶段，应同时改善渗透和抗侵蚀能力。这将通过在7YSZ上使用EB-PVD 65%-YZ(ZrO2-65wt%Y2O3)热障涂层和致密或渐变的SHVOF-Al_2O_3涂层来实现。基于真实微观结构的三维模拟模型应综合形态对渗透的影响，为进一步改进提供更科学的可能性，并更深入地揭示破坏机理。通过减少沉积数量的渗透将在温度梯度的循环条件下进行，以在涂层中提供更真实的应力状态。对于冲蚀实验，冲击角和颗粒尺寸的变化都在主要关注范围内，以模拟更接近涡轮的真实条件下的损伤发展。对影响侵蚀行为的各种因素进行量化的初步侵蚀模型将通过纳入其他方面加以扩大；对于大多数方面来说，还没有足够的数据。然后，这个侵蚀模型将揭示所有因素之间复杂的相互作用。

Damage of thermal barrier coatings (TBCs) in aero-engines and stationary gas turbines by deposits of calcia-magnesia-alumina-silica (CMAS) has gained increasing importance. At lower operating temper-atures erosion is another important damage phenomenon. The ultimate goal of this project is un-changed: to reveal the combined damage by CMAS and particle erosion, to get systematic correlations between the underlying parameters, and to discover the damage mechanisms of the TBCs under this complex loading situation. Therefore, the impact of CMAS infiltration on the erosion behavior was studied systematically for EB-PVD TBCs. In the first funding period it was found that the microstructure of 7YSZ has a large impact on CMAS infiltration kinetics, erosion resistance, and on the combined damage. Interestingly, the erosion resistance of infiltrated TBCs under perpendicular particle impact was often improved at the expense of mechanical integrity of the TBC. This is also valid for novel CMAS-resistant coatings such as Gd-zirconate and Al2O3. The chemistry of both deposit and TBC, and infiltration depth that would be different under a temperature gradient rule the formation of reaction phases and damage progression in the TBCs. First analytical models for the progress of infiltration, calculation of phases (Calphad), and measurements of mechanical properties correlate qualitatively well with experiments and open opportunities for improving the protective nature of the coatings and prediction of damage. Based on the results from the first funding period, both infiltration and erosion resistance shall be improved simultaneously during the second and final project phase. This will be achieved by using EB-PVD 65%-YZ (ZrO2-65 wt% Y2O3) TBCs and dense or graded SHVOF-Al2O3 coatings on top of 7YSZ. 3D simulation models based on real microstructures shall integrate the influence of morphology on infiltration, unfold more scientific based possibilities for further improvements and reveal the damage mechanisms in more depth. Infiltration by a reduced number of deposits will be performed under cyclic conditions in a temperature gradient to provide more realistic stress states in the coating. For the erosion experiments variation of both impact angle and particle size are within the main focus to simulate the damage progression under more realistic conditions that are similar to a turbine. The preliminary erosion model that quantifies various factors affecting the erosion behavior will be enlarged by incorporating additional aspects; for most of them sufficient data are not yet available. This erosion model will then reveal the complex interaction between all factors.