Air plasma spray (APS) thermal barrier coatings (TBCs) contain pores, cracks and splat interfaces that are preferentially aligned normal to the heat flux direction. These significantly reduce (by as much as 50%) the thermal conductivity over a fully dense coating. Here the microstructures of APS thermal barrier coatings (TBCs) have been characterised in 3D using X-ray micro-computed tomography (μ-CT). Pores larger than 2.8 μm 3 are resolved and their contribution to thermal conductivity reduction is evaluated using image-based microstructurally realistic numerical models. However, the models overestimate (by nearly 50 %) the measured thermal conductivity of the as-deposited TBC sample. It is shown that A cc ep te d A rt ic le This article is protected by copyright. All rights reserved. this discrepancy is due to very fine (micron and sub-micron) cracks which readily sinter after short term exposure to temperatures representative of TBC operating conditions causing the measured thermal conductivity to rise to within 15% of that predicted. This suggests that under the realistic service conditions, the 3D image-based models based on CT images provide a good indicator of the likely long-term TBC performance. Virtual experiments showed that for the retained pores, the larger pores which are flatter and more oriented in the plane of the APS splats, contribute disproportionately to the beneficial reduction in thermal conductivity. Our results demonstrate that X-ray imaging is a useful tool in establishing APS process conditions that gives rise to a beneficial distribution of such pores.

中文翻译：

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空气等离子喷涂热障涂层中孔隙率的 3D 表征及其对热导率的影响

空气等离子喷涂 (APS) 热障涂层 (TBC) 包含优先与热通量方向垂直排列的孔隙、裂纹和飞溅界面。这些显着降低（多达 50%）完全致密涂层的热导率。在这里，APS 热障涂层 (TBC) 的微观结构已使用 X 射线显微计算机断层扫描 (μ-CT) 在 3D 中进行表征。解析大于 2.8 μm 3 的孔隙，并使用基于图像的微观结构真实数值模型评估它们对热导率降低的贡献。然而，这些模型高估了（接近 50%）沉积态 TBC 样品的热导率。表明 A cc ep te d Art ic le 本文受版权保护。版权所有。这种差异是由于非常细小的（微米和亚微米）裂纹造成的，这些裂纹在短期暴露于代表 TBC 操作条件的温度后很容易烧结，导致测得的热导率上升到预测值的 15% 以内。这表明在现实服务条件下，基于 CT 图像的基于 3D 图像的模型提供了可能的长期 TBC 性能的良好指标。虚拟实验表明，对于保留的孔隙，更大的孔隙在 APS 板片的平面上更平坦且更定向，对热导率的有益降低贡献不成比例。我们的结果表明，X 射线成像是建立 APS 工艺条件的有用工具，可产生此类孔隙的有益分布。