Parameterization of the magnetite coating surfaces on low-carbon steel with the use of atomic force microscopy data

Abstract

The atomic force microscopy (AFM) technique is used to obtain information on the dynamic behavior of the magnetite coating (MC) formed on a steel 3 (St3) sample by chemical oxidation in a solution of ammonium nitrate. Digitized AFM data are the sets of profiles of chaotic roughness obtained via a sensing probe scanning over the surface fragment under study. The flicker noise spectroscopy (FNS) technique is used to analyze AFM images and to select parameters adapted to MC state characterization at the initial stages of formation. The FNS parameters introduced to characterize coating surfaces are calculated from spatial power spectra and transient structure functions. These parameters are considered to be the correlation lengths for different-type irregularities (jumps and spikes). Additionally, dimensionless parameters are introduced to characterize the loss of correlation in a series of irregularities when spatial intervals are substantially less than the correlation lengths. The performed FNS parameterization enabled us to obtain information on the state of the initial surface of St3 samples and to reveal the structural features intrinsic to the surface of MCs formed after different periods of oxidation. This information determines correlations between the elements of the MC structure and characterizes the properties of its microirregularities arising at different stages of coating formation.