Mass Balance and Atom Probe Tomography Characterization of Soft Magnetic (Fe65Co35)79.5B13Si2Nb4Cu1.5 Nanocomposites

Electric and magnetic properties, including saturation induction, resistivity, Curie temperature, and others, that make soft magnetic materials attractive for applications such as power converters and electric machines depend on local alloy composition. In this paper, we address this dependence quantifiably. First, we correlate the crystallization state to local composition with a novel mass balance. Second, we perform atom probe tomography on (Fe65Co35)(79.5)B13Si2Nb4Cu1.5 magnetic nanocomposites to explore local compositional evolution with devitrification and test predictions. Precise 3-D atom maps of constituent elements are constructed from as-cast, intermediate, and late stage crystallized samples. Local compositions and final crystal fraction predicted from mass balances are tested. Analysis of chemical partitioning during growth quantifies the depletion of glass formers (GFs) in nanocrystals, and enrichment of GFs and depletion of Fe and Co in the amorphous phase. Finally, we demonstrate the direct measurement of local composition on a nanometer scale and present predictive models necessary to deduce intrinsic constituent phase properties and investigate the proposed shell interfacial phases.