In-situ stress measurements of EB-PVD thermal barrier coatings using synchrotron x-ray diffraction under thermo-mechanical loading
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 powerful high energy X-rays (~80.7- 86 keV) at Sector I-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 various mechanical loads.
Synchrotron X-Ray Diffraction under thermo-mechanical loading has shown the existence of strain qualitatively within the diffraction patterns. Quantitative results obtained through Pseudo-Voigt peak fitting over selected peaks show the evolution of strain over a thermal cycle. In initial experiments, it was shown that mechanical loading at 32 MPa resulted in a tensile strain (£22 = 0.00053±0.00039 for 7 minutes) along the  atomic plane of a-AbO3 that was brief before going into strain relief in the compressive region but higher in magnitude than the 64 MPa (£22 = 0.00039±0.00024 for 14 minutes). Follow-on experiments indicate the presence of tensile strains within the bond coat region of the TBC system. After initial assessment of the effect of mechanical loading, our findings indicate that the effect of mechanical load during the cycle, often neglected in TBC studies, is of significance to the strain evolution within each cycle. This determination of critical conditions for strain evolution ( e.g. the first cycle) will serve to improve overall accuracy in life prediction of these coatings and contribute to developing methods of improving fatigue behavior.
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Bachelor of Science (B.S.)
College of Engineering and Computer Science
Mechanical and Aerospace Engineering
Dissertations, Academic -- Engineering and Computer Science;Engineering and Computer Science -- Dissertations, Academic
Length of Campus-only Access
Honors in the Major Thesis
Diaz, Rene Orlando, "In-situ stress measurements of EB-PVD thermal barrier coatings using synchrotron x-ray diffraction under thermo-mechanical loading" (2010). HIM 1990-2015. 1076.