| In the recent years, materials scientists have pay more and more attentions to the amorphous alloys, because of their excellent soft magnetic properties and potential industrial values. They have invented series of soft magnetic Fe-based bulk amorphous alloy systems with large glass forming ability. with the improvement of the glass-forming ability of Fe-based bulk amorphous alloy, the size of the amorphous samples can be producted larger. However, it was found that as the sample size increases, the soft magnetic properties of Fe-based bulk amorphous get worse. In other words, soft magnetic properties of the amorphous ribbons get better than the bulk amorphous alloys. Currently, there are few reports on the reasons why they have the different soft magnetic properties. This paper attempts to find the reason by using magnetic force microscopy. Based on this goal, this article contains the following works:Fe36Co36Si4B20Nb4 amorphous ribbons and 2 mm bulk amorphous rod were prepared by melt spinning method and copper mold casting method respectively. Then the soft magnetic properties of the amorphous ribbons and the 2 mm bulk amorphous rod were tested, and the magnetic topography of the two samples were also tested by magnetic force microscope. The result shows that:the soft magnetic properties of amorphous ribbons are better than that of 2 mm bulk amorphous rod; amorphous ribbons with high cooling rate during the preparation process has smaller magnetic anisotropy, wider magnetic domain structures and larger magnetic change cycle; On the other hand, the bulk amorphous alloys with a slower cooling rate during the preparation shows a certain degree of magnetic anisotropy and has a narrow magnetic domain structure and smaller magnetic transformation cycle.The cross-section of Fe66Co10Mo4P9C4B4Si4 bulk amorphous alloy with a diameter of 5 mm from the center to the edge was analysis by magnetic force microscope. The result shows that:different parts of the bulk amorphous alloy have different cooling rates during the rapid solidification process. The central part of the bulk amorphous alloy with a slower cooling rate which enhanced the development of atomic ordering, shows characteristics of magnetic anisotropy which is presented as a maze-like magnetic domain and smaller size of magnetic domain structure. On the other hand, the edge of the bulk amorphous alloy with a faster cooling rate which inhibits the process of atomic ordering shows a weaker magnetic anisotropy which is presented as a irregularly shaped domain wall, and wider magnetic domain structure.The Fe66Co10Mo4P9C4B4Si3 amorphous ribbons was prepared by melt spinning method, then the prepared amorphous ribbons was annealed at glass transition temperature at Tg, the peak temperature of first crystallization Tp and the end of peak temperature of the first crystallization Tedl respectively. And the magnetic properties were tested after the annealing process. The result shows that:annealing at the Tg temperature can significantly improve the soft magnetic properties:lower coercivity and higher permeability. However as the annealing time extended, the soft magnetic properties decreased, when the amorphous ribbons was annealed at the first crystallization peak temperature Tpl for 10 minutes, it showed excellent soft magnetic properties. However, when it was annealed for 30 minutes, because of the growing up of the crystalline phase, the soft magnetic properties became worse. When the amorphous ribbons was annealed at the end of a crystallization peak temperature Teal, the amorphous ribbons got sufficient crystallization power and its grain grow very quickly. As a result, the soft magnetic properties of the amorphous ribbons were damaged, and the annealed amorphous ribbons shows characteristics of paramagnetic. |
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