Noncontact methods for measuring thermal barrier coating temperatures

Three noncontact, optical methods for measuring temperature are reviewed with an emphasis on their application to the measurement of temperatures of thermal barrier coatings (TBCs). The methods are: infrared pyrometry, Raman spectroscopy, and photo-stimulated luminescence from lanthanide-doped coatings. Although each has the capability of measuring temperatures pertinent to monitoring TBCs, the finite thickness of typical coatings together with the optical properties of zirconia place severe restrictions on the depth from which the temperature sensing can be obtained. Some of these limitations can be circumvented using photo-stimulated luminescence with coatings containing dopants at specific locations. To illustrate this, it is demonstrated that by depositing coatings with a lanthanide dopant, such as Eu3+, at specific locations, for instance in contact with the metallic alloy, temperature sensing can be performed with much higher spatial resolution.