PNNL

Abstract

Magnetic properties including, saturation induction, resistivity, Curie temperature, etc., that make soft magnetic materials attractive for applications including power converters and electric machines, depend on local alloy composition. Addressing this dependence quantifiably, here we: 1) correlate crystallization state to local composition with a novel mass balance. 2) Atom Probe Tomography (APT) on (Fe65Co35)79.5B13Si2Nb4Cu1.5 magnetic nanocomposites is performed to explore local compositional evolution with devitrification and test predictions. Precise 3D 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, 3) this work demonstrates the direct measurement of local composition on a nanometer scale and presents predictive models necessary to deduce intrinsic constituent phase properties and investigate a proposed "shell" interfacial phases.