Assessing thermal barrier coatings by eddy current inversion

Nondestructive testing (NDT) of high temperature coatings is one of the imp ortant factors in achieving a high level of structural integrity in advance d gas turbines. In this paper, we demonstrate that sophisticated eddy curre nt techniques can be utilized to measure the thickness and remaining life o f high temperature coatings. Some research has been conducted to apply such techniques to the preservice case, for which the coating has one nicely de fined layer and nothing of consequence has diffused into the base metal tha t would create additional layers of anomalous material. We discuss the much more difficult inservice case, in which the time temperature exposure of t he combustion turbine blade has created a four layered system, in addition to the base metal.