Interface detection from laser drilling of air plasma-sprayed thermal barrier coatings by laser-induced breakdown spectroscopy

Abstract

To understand and control the laser machining process of cooling holes on thermal barrier coatings (TBCs) deposited on turbine blades, we introduced interfacial analysis based on laser-induced breakdown spectroscopy (LIBS). An integrated LIBS experimental setup was used to generate a series of craters under different laser shots to simulate the laser machining process. Based on the spectral data from LIBS, three characteristic atomic emission lines of Zr, Al, and Cr were selected for further analysis. We developed and revised a mathematical model based on laser ablation to understand the intensity variation of the three atomic emission lines. The experimental and model results confirmed a sharp intensity decrease of Zr at the ceramic layer/bond coat interface and observable intensity increases of Al and Cr at both the ceramic layer/bond coat and bond coat/substrate interfaces. We propose a first-order derivative method to further quantitatively obtain the interface location that can be used in practical applications.