Embedded Sensors for Thermal Barrier Coatings

Thermal Barrier Coatings (TBCs) are generally made of yttria-stabilized zirconia (YSZ). It has been found that when YSZ is doped with a rare-earth ion, such as terbium (Tb), it acts as a phosphor and is able to luminesce when excited by laser. Phosphors convert radiation of one wavelength at higher energy levels, to radiation of another wavelength at lower energy levels. The transition from high to low energy levels causes radiation emission in the visible light spectrum, or luminescence. This can be used to take temperature measurements at the TBC-bond coat interface of metal parts used in gas turbine engines. For this project, it is necessary to determine the appropriate concentration of terbia dopant and to investigate at what wavelengths laser excitation causes the doped YSZ to give off maximum luminescence intensity. Previous experiments have shown the luminescence intensity diminishes as the Tb concentration increases from 0.5% to 5.0%. This paper will present the effects of concentration on the luminescence property of Tb-doped YSZ and illustrate the possible uses in TBC embedded sensor.