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.

Measurement of Refractive Index and Thickness of Topcoat of Thermal Barrier Coating by Reflection Measurement of Terahertz Waves

“…(7) to (10) into Eq. (6), we obtain Equation (11) shows that Γ < 0, so that Γ = -|Γ|. Rearranging Eq.…”

Terahertz dielectric properties of plasma-sprayed thermal-barrier coatings

“…White et al [11] applied THz-TDS to the non-destructive evaluation (NDE) of yttria-stabilised zirconia (YSZ) coatings by imaging the thickness distribution and suggested that THz-TDS may potentially be used for the NDE of TBCs. Chen et al [12] investigated the dependence of the reflected THz time-domain waveform on the TGO thickness at the interface with an eye for using the TGO thickness to predict the remaining coating lifetime. However, they did not account for microstructure evolution, such as sintering and void growth, in the ceramic top layer during heat treatment.…”

Terahertz and Cultural Heritage Science: Examination of Art and Archaeology

“…There are other promising applications where THz has been tested even if less frequently. There is an increasing interest regarding THz application to detect and measure corrosion under paint for industrial applications [93][94][95][96]. This research could develop new THz methods for conservation of painted metal historical objects, such as furniture and sculptures.…”