Thickness determination of multiphase layer via combined Rietveld and Grazing Incidence X-ray diffraction approach

Plates of Maraging-300 steel with a chemically grown layer on the surface were prepared by heat treatment in superheated steam at different times. The grown coating on the martensitic substrate was characterized in terms of thickness, compositional and structural information by means of optical and scanning electron microscopies and by Grazing Incidence X-ray Diffraction (GIXRD). The results showed the presence of the hematite, magnetite, and austenite crystalline phases in two different sublayers composing the entire reacted layer: an austenite sublayer over the maraging substrate, and an oxide sublayer at the top, right above the austenite layer, composed of interspersed hematite and magnetite. Quantitative Phase Analysis by the Rietveld method under GIXRD was used to obtain the thicknesses of multiphase chemically reacted layers. The methodology and mathematical formalism are described. The comparison with estimated values from optical and scanning electron microscopy have shown a good agreement between the imaging and diffraction techniques, suggesting that the reacted layer increases progressively with the heat treatment time.