Crystallization characteristics in Co-based magnetic amorphous nanocomposites

Examination of the devitrification behavior of amorphous melt spun Co(78-x)Fe2MnxB14Si2Nb4 (x = 0.5 and 6.0%) alloys has been undertaken. These materials offer promising properties for use in high-power electronic systems where the microstructural evolution from processing is critical to developing permeability engineered, low-loss components. Transmission electron microscopy (TEM) and atom probe tomography (APT) reveal the precipitation of crystallites in the as-cast Mn 0.5% alloy, while such crystallites were absent in the as-cast Mn 6.0% alloy. After annealing at 400 °C for 10 min and 2 h, both alloys exhibit Co-rich nanocrystallites that are ≈3–5 nm in diameter while exhibiting little change in their crystal structure, morphology, and/or chemical partitioning behavior between each alloy or between the two annealing times. Short range ordering measurements determined from the atomic pair distribution function by electron diffraction reveals a modification of the second nearest neighbor bonding in these crystallites that is explained by the metastable incorporation of Fe into the crystallite. TEM and X-ray diffraction analyses reveal that annealing at longer times at 400 °C, i.e., for 3 h and 6 h for Mn 0.5% and Mn 6.0% respectively, results in a secondary precipitation of a transition metal (TM) boride phase, TM23B6, which is hundreds of nanometers in size.