X-ray Fluorescence Methods of Multilayer Coating Thickness Measurements on Satellite Launch Vehicle Components

Surface treatment technology has widened its horizon over various applications; from metal surfaces to modern high-tech polyurethanes Metallic hardware of satellite launch vehicles is applied with single and multilayer thermal barriers and other special metallic coatings to meet harsh environments and unflinching functional requirements. Tactile nondestructive evaluation and metrology methods are generally used to assess the thickness of these coatings. However, these cumulative methods cannot be relied upon for the individual layer thickness of multilayer coated components. The X-ray fluorescence method has emerged as a tool for the qualitative and quantitative determination of the layer thicknesses irrespective of single or multilayer coating. In addition to the Fundamental Parameter mode with and without the calibration standard, this study experiments with a new empirical mode with two calibration standards. It also investigates the consistency of  X-ray fluorescence measurements and the effects of infinite thickness and impurities on the coating thickness. As the X-ray fluorescence assessment of the underneath coatings shows large deviations, a simulation study is discussed to determine the correction factor to be applied at the specified thickness ranges. This study highlights the comparative advantages of the X-ray fluorescence method over the other conventional methods. This study also proves that the empirical mode is a promising X-ray fluorescence method for a better assessment of intermediate and undercoat thickness on multilayer coated metallic substrate in a single exposure.