High Energy X-rays Characterizing the Material Behavior of High Temperature Thermal Barrier Coatings

Abstract

ABSTRACT BODY: This study monitors the material behavior of Thermal Barrier Coatings (TBC) used on turbine blades. Samples tested consisted of 7-8 wt% YSZ applied by EB-PVD with a NiCrCaAlY bond coat. Monitoring of the phases in each layer and their material, mechanical and thermal characteristics under thermal gradient and mechanical loads gives insight into the behavior of these coatings at high temperature. High-energy synchrotron xrays were used to provide measurements with depth resolution through the bond coat and YSZ layers of 30 to 50 μm. X-ray diffraction patterns were taken using a 2D detector, giving accurate 360° lattice parameter measurement. The necessary information for the separation of lattice parameter changes between thermal expansion and residual mechanical strain was obtained by varying mechanical loading at high temperature. Monitoring lattice parameters such as c/a for the t’ YSZ phase gives insight into stabilizer concentration over cycling and corresponding load bearing capabilities. Additionally, these measurements give the susceptibility to phase transformations of the bond coat and its load bearing capability at high temperature under various loading conditions. Results from this study provide knowledge of how these coatings behave at high temperature and its dependence on phase and lattice parameters under variable real life thermal gradient and mechanical loads.