Microstructural investigation of a Fe-Co-Mo alloy by means of SANS and atom probe analysis

In order to design the properties of precipitation hardened steels, it is necessary to fully comprehend the principles that govern precipitation hardening. Small angle neutron scattering (SANS) is an analysis method that enables investigating nm-sized structures while simultaneously probing a large sample volume. However, for the interpretation of SANS patterns, assumptions about chemical, morphological and magnetic properties of the precipitates have to be made. For validating these assumptions, atom probe tomography (APT) is a valuable tool, since this method provides chemical information on the investigated material with near atomic spatial resolution. In this thesis the precipitation sequence of a model alloy (Fe-25 m% Co-15 m% Mo) was investigated by means of SANS and APT. Chemical and morphological properties of the precipitates, determined by APT, were used as input parameters in the models utilized for analyzing the SANS patterns. The precipitate radii and precipitate volume fractions obtained by SANS and APT were compared and the deviations discussed. Furthermore in this work, a new method was developed that corrects the cluster search results for artefacts that arise from performing analyses in AP datasets of varying density.