Laser induced breakdown spectroscopy for contamination removal on engine-run thermal barrier coatings

A method for cleaning thermal barrier coatings (TBCs) contaminated during engine operation has been developed using laser ablation. Surface contamination on the turbine blades hinders nondestructive remaining life evaluation using photoluminescence piezospectroscopy (PLPS). Real time monitoring of the removed material is employed to prevent damage to the underlying coating. This method relies on laser induced breakdown spectroscopy (LIBS) to compute the cross correlation coefficient between the spectral emissions of a sample TBC that is contaminated and a reference clean TBC. The ablation process is stopped when the LIBS signal indicates the presence of the underlying TBC. It is shown that it is possible to remove targeted contaminants and cease ablation at top surface of the TBC. Subsequent microscopy images and PLPS measurements indicate that the integrity of the TBC has been maintained during the removal of surface contaminants.