Measurement of coating thickness with X-ray diffraction

X-ray fluorescence (XRF) is frequently used to measure layer thickness in the micrometer range. But also X-ray diffraction (XRD) can be used in a comparable way and offers the benefit to differentiate coating layers by their crystal structure. Thus, the thickness of different oxide layers of the same element can be determined, e.g., FeO, Fe3O4, and Fe2O3 on Fe-substrate. An approach for such measurement is discussed. Furthermore, with a suitable sample stage, a spatially resolved coating thickness map can be measured in a nondestructive way. Applications and validations of the presented XRD method for the measurement of the thickness of zinc coatings on steel are given and compared with results from XRF, glow-discharge optical emission spectroscopy, and optical micrographs. In addition, the methodology was tested and validated using XRF reference standards and iron nitride and iron oxide layers.