Crystallization Characteristics in Co-Based Magnetic Amorphous Nanocomposite Alloys

This document will describe analytical procedures for the microstructural characterization of Co-based soft magnetic amorphous nanocomposite materials and the evolution of that microstructure after heat treatment. Atom probe tomography analysis of these alloys reveals increased chemical diffusion with additional solute content, as well as a reduction in defects in the crystalline phase. It was confirmed that Co and Fe partition preferentially to the crystalline phase, and that other elements (B, Si, Nb, Mn) segregate to the amorphous matrix. It was found that a combination of FCC/HCP structures were the basis for the crystalline phase.Differential scanning calorimetry was used to evaluate the characteristics of phase transition as a function of solute content, revealing an increase in the necessary energy for the formation of the primary crystallization phase with higher solute concentrations. From this data, the primary crystallization temperature was estimated and anneals were performed at a temperature just below that to slow the kinetics of crystallite nucleation and growth. Postmortem atom probe tomography and transmission electron microscopy data revealed that the alloy undergoes a constant nucleation condition, and that the added solute content suppresses the nucleation and growth behavior of both the primary and secondary crystalline phases.Finally, as strain annealing has been shown to improve the desired magnetic properties in these alloys, but the mechanisms are not yet understood, a method for applying digital image correlation techniques to tensile testing in an in situ tensile testing environment is described. This will establish precedent for applying these analyses to in situ tensile testing of sputter-deposited magnetic alloys, and eventually to in situ thermomechanical testing.