Phase transformation and magnetic properties of nanocrystalline Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 22.5-x/B/sub x/ (x=6,9) alloys

The coercivity and phase transformations of Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 22.5-x/B/sub x/ nanocrystalline alloys as a function of temperature (540 and 620 degrees C), annealing times (up to 240 min), and composition (x=6 and 9) are investigated by means of magnetic measurements, Mossbauer spectroscopy, and X-ray diffractometry. Nanocrystalline microstructure after annealing at 540 degrees C gives rise to a softening of the material, while, after annealing at 620 degrees C for short times, a magnetic hardening is observed before a significant increase in size of the alpha -Fe(Si) grains and the detection of a secondary Fe/sub 2/B phase. The initial stages of Fe/sub 2/B precipitation seem to be responsible for this magnetic hardening.<
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