| The development and characterization of FeCo-based nanocrystalline soft magnetic materials for high temperature applications is discussed. The material has been given the name HITPERM (pronounced hītēperm) and has compositions FeCo-M-B-(Cu), where M is an early transition metal (e.g. Zr, Hf, Nb) and Cu is an optional alloying element. Samples were prepared by a single wheel melt spinning technique followed by annealing for nano crystallization. The samples, in the form of ribbons, were characterized by the following techniques: differential scanning calorimetry (DSC), differential thermal analysis (DTA), conventional X-ray diffraction (XRD), synchrotron X-ray diffraction, extended X-ray absorption fine structure (EXAFS), transmission electron microscopy (TEM), Lorentz microscopy, vibrating sample magnetometry, superconducting quantum interference device magnetometry, and alternating current permeametry. Additional techniques through collaboration are included as appendices for support of the presented information. These include: atom probe field ion microscopy, magnetic force microscopy, and Mössbauer effect spectrometry.; The properties of the alloy primarily investigated (Fe44Co 44Zr7B4Cu1 annealed at 650°C for 1 hour) include: high relative permeability (up to 10,000), high magnetization to 980°C (2 T maximum induction), and low coercivity at room temperature and at a frequency of 5 kHz. Primary crystallization of the alloy began at 510°C with secondary crystallization at 700°C as determined by DSC and DTA. Primary crystallization provided the ferromagnetic α ′-FeCo phase as determined by synchrotron XRD. Grain sizes as determined by XRD and TEM were approximately 30 nm following a one hour anneal and about 60 nm in samples annealed at 600°C for up to 3072 hours. Minority phases found for the sample annealed for 3072 hours included ZrO and (Fe, Co)3Zr. |
