基于Finemet合金的成分及其非晶前驱体的晶化特征,提出了Finemet型合金的“双团簇”结构模型和团簇式成分,即Finemet合金的非晶前驱体可看作由2类团簇结构构成：一种为基于α-Fe(Si)有序固溶体(例如Fe3Si相)的[Si-Fe14](Cu1/13Si12/13)3弱稳定团簇结构;另一种为对应于Fe-B-Si-Nb系块体非晶合金的[(Si, B)-B2(Fe, Nb)8]Fe强稳定团簇结构。将2种团簇成分式按等比例混合,设计并制备了多个新成分合金。热分析和磁性测量结果表明,所有成分的非晶样品均显示多峰晶化特征,其中,[(Si0.8B0.2)-B2Fe7.2Nb0.8]Fe+[Si-Fe14](Cu1/13Si12/13)3 (即Fe74B7.33Si15.23Nb2.67Cu0.77)非晶两晶化峰的峰间距(ΔTp=Tp2-Tp1)最大,约为192 K。该非晶样品在813 K等温退火60 min后获得典型的纳米晶/非晶复相结构,其饱和磁化强度Bs约为1.26 T,矫顽力Hc约为0.5 A/m,1 kHz下的有效磁导率μe约为8.5×105。新成分纳米晶合金的综合软磁性能均优于典型成分为Fe73.5Si13.5B9Cu1Nb3的已有Finemet纳米晶合金。
The development of nanocrystalline Fe-Si-B-Nb-Cu alloys, commercially known as Finemet, has established a new approach to obtain soft-magnetic materials with high magnetic flux density. The material consists of α-Fe(Si) nanocrystals embedded in an amorphous matrix, which is made by means of partial crystallization. The composition and local structure of the precursor amorphous alloys are crucial for the formation of the unique nanocrystalline structure. The present study is devoted to understanding the composition characteristics and developing new compositions of Finemet alloys. Using the “cluster-plus-glue-atom” model and noticing the crystallization characteristic of Finemet alloy, a “dual-cluster” amorphous structure model is proposed. In this model, the precursor amorphous structure of Finemet alloy is considered to contain a mixture of the [(Si, B)-B2(Fe, Nb)8]Fe cluster derived from the Fe-B-Si-Nb bulk glassy alloys, and the [Si-Fe14](Cu1/13Si12/13)3 cluster from Fe3Si phase. A series of new Finemet nanocrystalline alloy compositions are designed by mixing [(Si, B)-B2(Fe, Nb)8]Fe and [Si-Fe14](Cu1/13Si12/13)3 cluster formulas with a ratio of 1∶1. Thermal analysis results show that [(Si0.8B0.2)-B2Fe7.2Nb0.8]Fe+[Si-Fe14](Cu1/13Si12/13)3 (alloy composition: Fe74B7.33Si15.23Nb2.67Cu0.77) amorphous alloy exhibits a maximal temperature interval of about 192 K between the first and second crystallization peaks. Magnetic measurement results show that the Fe74B7.33Si15.23Nb2.67Cu0.77 nanocrystalline alloy exhibits optimal soft magnetic properties with a saturation magnetization Bs about 1.26 T, a coercive force Hc about 0.5 A/m and an effective permeability μe about 8.5×105 at 1 kHz after isothermal annealing at 813 K for 60 min. The soft magnetic properties of the new composition nanocrystalline alloys are better than that of the typical Finemet nanocrystalline alloy (Fe73.5Si13.5B9Cu1Nb3).
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