Monitoring thermal barrier coating delamination progression by upconversion luminescence imaging

Jeffrey I. Eldridge, Douglas E. Wolfe

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Upconversion luminescence imaging provided contrast for monitoring thermal barrier coating (TBC) delamination progression during interrupted furnace cycling to 1163 °C, with sensitivity even for early stages of subcritical delamination crack propagation. Image contrast for delamination monitoring is obtained because delamination cracks introduce an interface between a higher (TBC) and lower (air) index of refraction medium so that total internal reflection beyond a critical incident angle occurs for both the excitation and emission wavelengths. Therefore, considerably greater luminescence emission is observed from regions containing delamination cracks. Upconversion luminescence produces exceptional image contrast because background fluorescence is very low when the detected emission is at a substantially shorter wavelength than the excitation. The upconversion luminescence emission was excited within a 6 μm thick Er3+/Yb3+ co-doped yttria-stabilized zirconia YSZ (YSZ:Er,Yb) layer beneath a 130 μm thick undoped YSZ layer, sequentially deposited with no interruption by electron-beam physical vapor deposition (EB-PVD) onto a NiPtAl bond-coated superalloy substrate. Excitation at 980 nm produced upconversion luminescence emission from Er3+ at 562 nm after two sequential energy transfers from Yb3+ co-dopant ions. Upconversion luminescence imaging, supported by scanning electron microscope inspection of interfacial damage, revealed that delamination progression proceeded by the formation of isolated microdelaminations with large separations between the TBC and thermally grown oxide (TGO) along with small-separation microcracks that propagated in the regions between the microdelaminations. In addition, upconversion luminescence imaging of the extent of delamination produced by Rockwell indentation clearly showed that the TBC becomes increasingly susceptible to mechanically induced damage throughout its cyclic life.

Original languageEnglish (US)
Article number124923
JournalSurface and Coatings Technology
StatePublished - Nov 25 2019

All Science Journal Classification (ASJC) codes

  • General Chemistry
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Materials Chemistry


Dive into the research topics of 'Monitoring thermal barrier coating delamination progression by upconversion luminescence imaging'. Together they form a unique fingerprint.

Cite this