Speaker
Description
A fast and non-destructive method based on X-ray diffraction for phase quantification in zinc alloyed coatings is presented. Post-annealed hot-dip galvanized steel sheets may contain various Fe/Zn alloys (Γ-Fe3Zn10, Γ1-Fe11Zn40, δ-Fe13Zn126, ζ-FeZn13) arranged in a layered conformation and with a predictable stacking order. Each phase within the coating has a different crystalline structure implying a heterogeneous mechanical behaviour: the phase quantification is therefore crucial for controlling further product behaviour, i.e. formability under press.
The determination of the individual layer thicknesses remains a challenging, time consuming and typically destructive task. Compared other methods, X-ray diffraction provides a unique fingerprint for each alloy constituting the coating. The so-called Rietveld method typically applies to an infinitely thick (compared to x-ray penetration depth) and homogenous mixture of phases. In the software TOPAS, the industry standard for quantitative phase analysis, the Rietveld method can be adjusted to a conformation of stacked phases by applying additional corrections related to (i) limited layer thicknesses and (ii) x-ray absorption through successive layers. A calibration of the beam flux allows for consideration of layer thicknesses as refinable parameters, acting then as unique scaling factors for each phase. Consequently, TOPAS delivers fast (few seconds of refinement), meaningful and absolute quantification results. Further coating parameters like coating weight, chemical alloying or phase ratios can be derived from the refined layer thicknesses.
A dedicated industrial diffractometer, D8 ENDEAVOR, equipped with an optimized diffraction geometry (DBO) provides high quality data in short measurement times (few minutes). No sample preparation, fast data acquisition, a large sample magazine with 66 positions and a fully automated evaluation contribute to an ideal solution in QC environment with high sample throughput.
Keywords
zinc alloyed coating phase structure, high-throughput x-ray diffraction, Rietveld method