Acquisition Techniques for Synchrotron XRay Strain Measurements in Tubular TBC Specimens for Thermal Gradient Mechanical Testing

Abstract

This research aims to develop techniques to accurately obtain in-situ strain measurements of thermal barrier coating systems (TBCs) applied to tubular specimens. EB-PVD coated tubular samples with internal cooling were designed to achieve realistic temperature drops over the TBC coatings. Effects of the circular cross-section on the x-ray diffraction (XRD) strain measurements in the various layers, including the thermally grown oxide (TGO), are investigated using a high energy synchrotron operating at 86 keV. Multiple approaches for beam penetration, including both tangential and normal to the layers, along with variations in collection parameters are compared for their ability to attain high-resolution XRD rings of the internal layers. To account for the measurement through the layers, results from the acquisition techniques are analyzed to isolate the diffraction rings of the various materials. The techniques are compared to experiments aligning the x-ray beam parallel to the in-plane direction of flat specimens, providing insight for the compensation of the non-symmetrical material composition in the diffraction volume. Results are used to summarize the various techniques for obtaining depth-resolved strains through multi-layered coating systems. The outcomes will pave the way towards goals in achieving realistic in-situ testing of these coatings.