Multiple wavelength stratigraphy by laser-induced breakdown spectroscopy of Ni-Co alloy coatings on steel

The rapid qualitative and quantitative stratigraphic analysis of metal coatings is of substantial importance in modern industrial applications. Laser-Induced Breakdown Spectroscopy (LIBS) is presented as an attractive option to obtain fast and reliable stratigraphic results. There are still urgent optimization needs particularly in respect to metal coating systems. In this investigation, radiation of the harmonic wavelengths at 1064, 532, 355 and 266 nm of a nanosecond pulsed Nd:YAG laser were used to ablate a steel sheet galvanically coated with a 20 μm layer of a Ni-Co alloy. Atomic emissions from the resulting plasmas were recorded and converted into stratigrams by the linear correlation coefficient method. For all wavelengths, the average ablation rate as a function of laser fluence, as well as the effective absorption coefficient were determined and compared to predictions based on a simple wavelength-independent heat diffusion model. This study enables a deeper mechanistic understanding and an optimization of a high-precision stratigraphy of metal coating systems.