Nanocluster formation in oxide-dispersion strengthened steels by internal oxidation subsequent to ultrasonic powder atomization

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The proposed project deals with the fundamental issue in processing oxide dispersion strengthened steels of how oxide nanoclusters form from the severely deformed microstructure subsequent to mechanical alloying. In this project, we utilize ultrasonic metal powder atomization for this purpose, which allows the preparation of metal powders lean in interstitials. During ultrasonic metal powder atomization, the raw material is melted in an arc melter the crucible of which is attached to an ultrasonic sonotrode. The vibrations of the sonotrode lead to tear off of molten particles and rapid solidification to spherical particles with narrow size distribution occurs. The use of arc melting and low gas flow allows for achieving very low interstitial contents. These are below or in the order of the oxygen contents needed to form oxide nanoclusters whereas in mechanical alloyed steels a tremendous oxygen excess exists which makes the analysis of the solved oxygen content and precipitation state of the oxides difficult. After atomization, the nanoclusters are formed via internal oxidation. During the project, the chemical composition, the microstructure and the mechanical properties are determined throughout the entire processing chain. This includes an evaluation of oxide particle size and density, dislocation density and grain size by scale-bridging characterization techniques. This allows for an assessment of the precipitation sequences during the processing steps and its influence on the mechanical behavior of the materials.