Abstract
This work investigated processing of stainless steel powders and powder mixtures using powder bed fusion - laser beam/metal (PBF-LB/M), which produced different ferritic and austenitic phase fractions in the as-built state. The rapid cooling and solidification rates in the PBF-LB/M process led to the formation of an extremely small-structured microstructure in which the austenitic phase was found on the grain boundaries and as acicular Widmanstätten austenite (width < 1 µm) within the primary δ-ferritic solidified matrix. This work shows that the time-saving quantification of the ferritic and austenitic phase fractions of these particular microstructures is nontrivial. Common time-efficient phase quantification methods such as image analysis of etched cross-sections or magneto-inductive methods (Feritscope®) have proven to be inaccurate. On the other hand, electron backscattered diffraction (EBSD) investigations proved to be extremely time-consuming in order to resolve the small microstructural constituents sufficiently well and to obtain a reliably large sample section. The highest accuracy was achieved with X-ray diffraction. Two different methods were considered: the Debye-Scherrer method, which was characterized by short measuring times, and the Bragg-Brentano method (quantification using Rietveld refinement), which showed the highest accuracy for the entire range of ferritic-austenitic phase fractions.
Published Version
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