Sensor TBCs: Remote In-Situ Condition Monitoring of EB-PVD Coatings at Elevated Temperatures

Abstract

Thermal Barrier Coatings (TBC) are used to reduce the actual working temperature of the high pressure turbine blade metal surface. Knowing the temperature of the surface of the TBC and at the interface between the bondcoat and the thermally grown oxide (TGO) under realistic conditions is highly desirable. As the major life-controlling factors for TBC systems are thermally activated, therefore linked with temperature, this would provide useful data for a better understanding of these phenomena and to assess the remaining lifetime of the TBC. This knowledge could also enable the design of advanced cooling strategies in the most efficient way using a minimum amount of air. The integration of an on-line temperature detection system would enable the full potential of TBCs to be realised due to improved precision in temperature measurement and early warning of degradation. This in turn will increase fuel efficiency and reduce CO2 emissions. The concept of a thermal-sensing TBC was first introduced by Choy, Feist and Heyes in 1998 [1]. The TBC is locally modified so it acts as a thermographic phosphor. Phosphors are an innovative way of remotely measuring temperatures and also other physical properties at different depths in the coating using photo stimulated phosphorescence [2]. In this study the temperature dependence of several rare earth doped EB-PVD coatings will be compared. Details of the measurements, the influence of aging, the composition and the fabrication of the sensing TBC will be discussed in this paper. Temperature detection at ultra-high temperatures above 1300°C is presented using new types of EBPVD TBC ceramic compositions. Multilayer sensing TBCs will be presented, which enable the detection of temperatures below and on the surface of the TBC simultaneously.