In-Situ Strain Measurements of EB-PVD Thermal Barrier Coatings using Synchrotron X-Ray Diffraction under Thermo-Mechanical Loading

摘要

Demands for designing prime reliant, energy-efficient, and high performance thermal barrier coatings (TBCs) in gas turbines have led to a growing interest toward comprehensive microstructural characterization. Over the last decade, Synchrotron X-ray Diffraction (XRD) has established itself as a high-resolution strain measurement method for the thermally grown oxide (TGO) layer of thermal barrier coatings (TBCs). In this work, we present in-situ X-ray strain measurements of the TGO layer on cycled TBC specimens under thermo-mechanical loading using high energy X-rays (~80.7- 86 keV) at Sector 1-ID of the Advanced Photon Source at the Argonne National Laboratory. The evolution of TGO stresses was examined over one complete thermal cycle on TBC samples at various stages of the life fraction under mechanical loads. Quantitative results obtained through Pseudo-Voigt peak fitting of the (024) and (300) planes of a-Al_2O_3, show the evolution of strain in-situ over a thermal cycle. It was shown that increasing mechanical load resulted in reduced compression during a cycle to the point where tensile strain was observed in the TGO. This determination of critical conditions for strain evolution in early cycle specimens will serve to improve overall accuracy in life prediction of these coatings and contribute to developing methods of improving fatigue behavior.