Concepts for luminescence sensing of thermal barrier coatings

The basis for a number of concepts for in-situ monitoring thermal barrier coatings using non-contact luminescence is described. Restrictions imposed by phase compatibility with the thermally grown oxide formed between the bond-coat and the coating, as well as with the thermal barrier coating material are described. This naturally leads to the selection of rare-earth ions incorporated into the crystal structure of the coating, whether YSZ or one of the rare-earth pyrochlores, as appropriate chromophores. A rare-earth sensor embedded in a YSZ coating prepared by electron-beam deposition is demonstrated as well as a “rainbow” sensor.