Crystallization and magnetic behaviour of Fe-Nb-Cu-Si-B alloys

Abstract

The crystallization and magnetic properties of Fe_72.5Nb_4.5Cu₁Si₁₀B₁₂, Fe_73.5Nb₃Cu₁Si_13.5B₉ and Fe₇₂Nb_4.5Cu₁Si_13.5B₉ alloys have been studied. After primary crystallization, the α-Fe(Si) phase was formed for the alloy which has 10 at.% Si. The ordered Fe₈₀Si₂₀ phase was formed for alloys containing 13.5 at.% Si. The activation energy for the formation of the α-Fe(Si) phase was 67 kcal mol¹, which is lower than that for the formation of the ordered phase. In the scannins temperature variation or resistivity measurement, a drop in resistivity was found during the formation of the α-Fe(Si) phase whereas a rise in resistivity was observed during primary crystallization for the other two alloys. Grain-boundary scattering and the low-temperature coefficient of resistivity were the causes of the rise in resistivity during the formation of the ordered phase. The Fe₇₂Nb₄₅Cu₁Si_13.5B₉ alloy exhibited superior soft-magnetic properties among the measured alloys when annealed between 875 and 875 K for 30 min. The rapid deterioration in the magnetic properties at higher temperatures of the annealed alloys was primarily due to the formation of the Fe₂B phase, which has a strong magnetocrystalline anisotropy energy.