Simple procedure to establish thickness and phase composition of plasma nitrided and post-oxidized steel surfaces using multiple angle GIXRD and RIR quantification

Abstract

Multiple angle grazing incidence X-ray diffraction (GIXRD) was employed to determine depth distribution and thickness of different phases developed on steel, after plasma nitriding and post-oxidation, establishing a method that is fast, simple and widely applicable to characterize different types of polycrystalline coatings. Diffractograms were acquired with incidence angles between 0.25° to 10° and the phase weight fraction was calculated using the RIR method. The probed depth was determined using the weighted average of the X-ray mass absorption coefficients of the obtained phases. Utilizing peak appearance order, weight fraction, density, and probed depth, a structure of pure or mixed phases is discussed. Conversion electron Mössbauer spectroscopy, which probes to a similar deepness as 0.75° GIXRD, was used to corroborate the phase composition of this depth. Validation of thickness was achieved through SEM images acquired from micrometric trenches milled on the surface, using a focused ion beam. Coefficient of friction tests were conducted to investigate the correlations between coefficient of friction with phase composition, and durability with the thickness of the outer layer. The characterization procedure presents information on the concentration and depth where the phases are located, the coating thickness and roughness. The findings are supported by additional analytical techniques.