title: Pulsed-terahertz reflectometry for health monitoring of ceramic thermal barrier coatings.
abstract: Terahertz time-domain reflectometry was used to monitor the progress of a thermally grown oxide layer and stress-induced, air-filled voids at the interface of an Yttria-stabilized-zirconia ceramic thermal-barrier coating and a metal surface. The thicknesses of these internal layers, observed in scanning-electron-microscope images to increase with thermal-exposure time, have been resolved - even when changing on the order of only a few micrometers - by distinguishing not only increased delays in the arrival times of terahertz pulses reflected from this multilayer structure, but also changes in the width and shape of the pulses. These unique features can be used to predict the lifetime of thermal-barrier coatings and to indicate or warn of spallation conditions. The trends of the experimental results are also confirmed through Fresnel-reflection time-domain simulations.
authors.affiliation: Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48109, USA. galenc@umich.edu
authors.forename: Chia-Chu
authors.initials: CC
authors.lastname: Chen
authors.forename: Dong-Joon
authors.initials: DJ
authors.lastname: Lee
authors.forename: Tresa
authors.initials: T
authors.lastname: Pollock
authors.forename: John F
authors.initials: JF
authors.lastname: Whitaker
mesh_terms: D002516:Ceramics / Q000032:analysis* / Q000737:chemistry*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006358:Hot Temperature; D008422:Materials Testing / Q000295:instrumentation*; D010783:Photometry / Q000295:instrumentation*; D055068:Terahertz Spectroscopy / Q000295:instrumentation*