Abstract
Ultra-Rapid Annealing (URA) has been demonstrated as a viable means of producing nanocrystalline soft magnetic materials with a saturation magnetic polarization comparable to that of Fe-Si steels (1.85 to 2.02 T) while also maintaining low coercivity (2.5 to 9.3 A/m)[1–3]. However, the high heating rates (> 104 K/s) and short annealing times (< 3 s) utilized by URA compared to conventional annealing techniques, along with the effect of latent heating during primary crystallization [4], has created new material production challenges. Specifically, the requirement for batch processing by URA places a limit on the commercial viability of this technique. In this work, a Continuous Ultra-Rapid Annealing (CURA) process has been demonstrated whereby a ribbon undergoes URA in a reel-to-reel continuous process. Annealing time (0.1 to 10 s) and tension (5-40 MPa) utilized by CURA are carefully controlled to allow for the processing of brittle nanocrystalline alloys. The microstructural and magnetic properties of nanocrystalline (Fe0.8Co0.2)86B14 produced by CURA have been characterized. Figure 1 shows DC hysteresis loops acquired from nanocrystalline (Fe0.8Co0.2)86B14 produced by the batch URA [1,2] and the newly developed CURA processes. The coercivity was reduced from 14.9 A/m to 8.8 A/m and the core loss at 1.5 T and 50 Hz was reduced from 0.62 W/kg to 0.50 W/kg by applying the CURA process. The CURA process has also been utilized to produce a nanocrystalline (Fe0.8Co0.2)86B14 toroidal core weighing 0.16 kg. This core was machined to produce a stator core for a commercially available 220 W electric motor which demonstrated a 10-25% relative improvement in efficiency over an unmodified motor with a conventional Fe-Si steel stator core [5].  DC hysteresis loops acquired from nanocrystalline (Fe0.8Co0.2)86B14 produced by conventional Ultra-Rapid Annealing (URA) and the newly developed Continuous Ultra-Rapid Annealing (CURA) process.  A photo of the nanocrystalline (Fe0.8Co0.2)86B14 electric motor stator core produced by CURA after winding of the excitation coils and mounting to a commercially available 220 W motor frame.
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