Dr John Day and Scott Greenwell at the Interface Analysis Centre, University of Bristol, have been using a VS60 from our VS range of cameras to image the Aluminium Oxide (Alumina) used as a protective coating for turbine blades by Rolls-Royce PLC*. The Alumina contains small traces of Chromium impurity absorbed from the superalloy used to manufacture the turbine blade. Chromium doped Alumina exhibits the same fluorescence response as Ruby with two extremely sharp and intense red emission lines at around 693nm. By imaging the blades under green light with an Atik camera and a tuneable filter set to 693nm pass band they can image the Alumina directly and then, by tuning to a nearby wavelength, image any other contaminants that may also fluoresce in that region. The difference in the two images provides a rapid way of determining the integrity of the protective coating.
* “Development of an imaging system for the detection of alumina on turbine blades” Greenwell, S; Kell, J; Day, J. Meas. Sci. Technol. 25 (2014) 035902 (6pp).
- a) shows a reflected light image of a turbine blade annotated by a marker pen.
- b) shows a fluorescence image with bandpass filter set to 693nm , showing Alumina and contribution from other fluorescent contaminants
- c) shows fluorescence image with filter set to 670nm bandpass, rejecting Alumina contribution at 693nm
- d) Image c is subtracted from image b to show alumina coverage on the turbine blade surface.