| Due to its excellent soft magnetic properties amorphous-nanocrystalline Finemet alloy is now being widely used in many areas, such as power transformer, inductance materials, precision current transformer and etc. Some progress has been made on the compositions design and elemental doping of Finemet alloy. However, further researches are needed to prepare the Finemet alloy with higher saturated magnetic induction and lower coercive force on the basis of having sufficient strong mechanical properties. In this thesis, the effects of composition, microstructure and elemental doping on the magnetic and mechanical properties of Finemet alloy were studied:(1) The effect of different content of Cu on the thermal stability, soft magnetic and mechanical properties of Fe74.29-xCuxNb2.9Si13.56B9.25(x=0.8-1.1) alloy was analyzed. The results showed that:when the Cu content is0.9at.%, the average grain size of annealed ribbons is15nm which is the minimum value among all the Fe74.29-xCuxNb2.9Si13.56B9.25(x=0.8-1.1) alloys studied and the alloy has the best soft magnetic properties with a saturated magnetic induction Bs of1.26T, an effective magnetic permeability μe of120800and the lowest core loss value. Meanwhile, the alloy has the best mechanical properties with a Vickers hardness of778Hv and the highest flexural plasticity.(2) The effect of different content of Nb on the soft magnetic and mechanical properties of Fe73.37-xCu0.92NbxSi13.56B9.24(x=2.6,2.7,2.8,2.9at.%) alloy ribbons was analyzed. The results obtained by analyzing the microstructure, density, magnetic and mechanical properties of alloys showed that:when the Nb content is2.9at.%, the initial magnetic permeability μi is about127000and the coercive force is0.0088Oe. Meanwhile the alloy has the minimum core loss on each of the measuring frequencies. When the Nb content is2.8at%, the alloy has the highest density of6.97g/cm3and the best mechanical properties among the studied alloys.(3) Fe-Cu-Nb-Mo-Si-B alloy ribbons used in precision current transformer were fabricated by spin melting technology. The optimum annealing temperature was determined by measuring the initial magnetic permeability μi of the alloy ribbons at different annealing temperatures. It was found that the optimum annealing temperature decreased with the increase of Mo content. Meanwhile, the effect of different content of Mo on the soft magnetic and mechanical properties of this Finemet system alloys was studied. The results showed that:when the Mo content is2at.%, the DC magnetic and mechanical properties of the alloys are the best; and when the Mo content is lat.%, the value of core loss is the minimum indicating its optimum AC magnetic property and the hardness of the alloy reaches the highest value of785Hv.(4) Fe-Cu-Nb-V-Si-B alloys used for inductance materials were fabricated by spin melting technology with V doping. The effect of different content of doped V on the magnetic properties of this Finemet system alloys was studied. The results showed that:when doped V content is lat.%, both DC and AC magnetic properties are the best, and both Vickers hardness and flexural plasticity of the alloy are also the best with the values of785Hv and0.100respectively.(5) By analyzing the distribution and size of nano-crystallite, micro-Vickers hardness and flexural plasticity of the annealed alloys, the effect of trace doping of rare earth element Ce on the microstructure, soft magnetic and mechanical properties of Finemet alloy was studied. The results showed that:when doped Ce content is0.4at.%, the thermal stability temperature range of the alloy, AT, is up to176℃, which is the maximum value achieved for the Ce-doped alloys. Meanwhile the soft magnetic and mechanical properties of this alloy are also the best. The distribution and size of nano-crystallite in the alloy are believed to directly relate to the change of magnetic and mechanical properties of Finemet alloy. |
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