Synchrotron XRD Measurements of Thermal Barrier Coatings Subjected to Loads Representing Operational Conditions of Rotating Gas Turbine Blades

Abstract

High-energy synchrotron x-rays were used in this work to monitor the internal strain behavior of Thermal Barrier Coatings (TBC) under thermal gradient and mechanical loading. Tubular specimens made from Nickel based super alloy with a TBC-system applied onto the outer surface by Electron Beam Physical Vapor Deposition were used to allow for cooling of the internal surface of the substrate while heating the external surface during thermal mechanical cycling. The coating system consisted of a Yittria Stabilized Zirconia (YSZ) top coat and a MCrAlY bond coat. Through transmission along with a 2D detector allowed for the 2D strain monitoring of each layer during high temperature operation. Monitoring the micro-strain of each phase within the layers provides insight into their high temperature behavior which can be used to further develop predictive models including evolution of elastic strain as well as creep and plasticity. Obtained results have shown a large variation in strains during ramp up of in-phase thermal and/or mechanical load with a significant tensile strain mismatch between the two prominent phases of the bond coat. The YSZ has displayed residual compressive strains at the bond coat/YSZ interface and maintained some compressive residual strain during high temperature holds. These results give valuable insight into the mechanics of these complex systems under various high temperature conditions.