Study on soft magnetic properties of Finemet‐type nanocrystalline alloys with Mo substituting for Nb

The thermal stability, microstructure, and soft magnetic properties as a function of annealing time were studied for Fe73.5Si13.5B9Cu1Nb3−xMox (x = 0, 1, 2, 3) (atom percent, at.%,) ribbons. It was found that substituting Nb by Mo reduced the thermal stability. After 15 min short time vacuum annealing, Fe73.5Si13.5B9Cu1Nb2Mo1 and Fe73.5Si13.5B9Cu1Nb1Mo2 samples obtained higher permeability and similar coercivity compared to the original Finemet alloy (Fe73.5Si13.5B9Cu1Nb3), Mo substituting Nb reduced the optimum annealing time in Finemet-type alloys, and meanwhile marginally increased the saturation magnetization. Substituting all Nb by Mo led to the earlier formation of non-soft magnetic phase, thus deteriorated the soft magnetic properties. XRD and TEM structural analysis showed that in Fe73.5Si13.5B9Cu1Nb2Mo1 and Fe73.5Si13.5B9Cu1Nb1Mo2 samples (annealed for 15 min), nanocrystals ∼10 nm in size were obtained, and the good soft magnetic properties of these alloys could be attributed to the small grain size. The relationship between annealing time, soft magnetic properties, and microstructure was established. Reducing annealing time and temperature to obtain best soft magnetic properties could cut down the production costs of Finemet-type alloys.

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