THz Time-Domain Reflectometry (TDR) has been applied to the accurate measurement of the thickness of yttria-stabilized-zirconia (YSZ) thermal-barrier coatings that commonly reside on the surface of turbine-engine components. Several reflectometer configurations have been assembled and are available, and a thickness resolution of < 10 micrometers has been achieved. Results have demonstrated the potential of THz-TDR for the effective monitoring of thermal-barrier-coating-layer thickness, particularly in the production environment.
A joint investigation between Prof. Tresa Pollock and the Ultrafast Microwave Photonics group has concentrated on the behavior of time-domain reflection signatures of YSZ coatings versus thermal-cycling – and thus also thermally-grown-oxide – conditions. Analysis of the temporal reflections and SEM images has revealed a quantitative correlation between the THz-signal characteristics and the thermally-grown-oxide thickness.