利用“团簇加连接原子”模型设计和优化具有高形成能力的Fe-B-Si-Nb块体非晶合金. 以源于Fe-B二元共晶相的Fe2B局域结构为基础, 结合电子浓度判据, 构建Fe-B二元理想非晶团簇式[B-B2Fe8]Fe; 考虑到原子间混合焓的大小, 选择Si和Nb原子分别替代[B-B2Fe8]团簇的中心原子B和壳层原子Fe, 得到[Si-B2Fe8-xNbx]Fe系列四元非晶成分. 结果表明, [Si-B2Fe8-xNbx]Fe团簇式在x=0.2~1.2成分处均可形成块体非晶合金, 其中在x=0.4~0.5的成分区间内均可形成临界尺寸为2.5 mm的块体非晶合金. 考虑到原子半径的大小, 鉴于增加Nb的同时降低Si的含量可维持[Si-B2Fe7.6Nb0.4]Fe非晶团簇结构的拓扑密堆性, 由此得到另一系列[(Si1-yBy)-B2Fe8-xNbx]Fe团簇式成分. 结果表明, 在(x=0.5, y=0.05)~(x=0.9, y=0.25)成分区间内均可通过Cu模铸造法获得直径为2.5 mm的块体非晶. 新设计获得的Fe-B-Si-Nb块体非晶合金具有优良的室温软磁性能和力学性能, 其中[Si-B2Fe8-xNbx]Fe (x=0.2~0.6)非晶合金的饱和磁化强度为1.14~1.46 T, 矫顽力为1.6~6.7 A/m; [(Si0.95B0.05)-B2Fe7.5Nb0.5]Fe块体非晶合金的室温压缩断裂强度达4220 MPa, 塑性形变约为0.5%.
Fe-based amorphous alloys are well known for their good magnetic properties including ultrahigh saturation magnetization, low coercive force, high magnetic permeability and low core loss. But these alloys were only prepared into ribbon form in early times due to their insufficient glass-forming abilities (GFAs). The present work focuses on the design of Fe-B-Si-Nb bulk metallic glasses with good soft magnetic properties and high glass-forming ability. Glass formation in Fe-B system is first considered with cluster-plus-glue-atom model. A basic composition formula [B-B2Fe8]Fe is proposed as the framework for multi-component alloy design. Considering the structural stability of the model glass, Si and Nb are introduced to the [B-B2Fe8] cluster to replace the center B and shell Fe atoms, from which a series of Fe-B-Si-Nb alloys with composition formulas [Si-B2Fe8-xNbx]Fe (x=0.1~1.2) are derived. Copper mold casting experiments revealed that bulk glass alloys with a critical diameter (dc) exceeding 1.0 mm are readily obtained with the Nb content range of x=0.2~1.2, the largest dc (about 2.5 mm) appears in the vicinity of x=0.4~0.5. Considering the local packing efficiency of Fe-B-Si-Nb glass model structure, another series alloy compositions, namely, [(Si1-yBy)-B2Fe8-xNbx]Fe is reached by increasing Nb and decreasing Si simultaneously in [Si-B2Fe7.6Nb0.4]Fe basal glass alloys. The experimental results show that bulk glass alloys with dc=2.5 mm are available over a wide range of compositions from (x=0.5, y=0.05) to (x=0.9, y=0.25). Excellent magnetic softness with high saturation magnetizations (Bs=1.14~1.46 T) and low coercive forces (Hc=1.6~6.7 A/m) is found in the [Si-B2Fe8-xNbx]Fe (x=0.2~0.6) series glass alloys. A high fracture strength of 4220 MPa with a plasticity of 0.5% is observed in the [(Si0.95B0.05)-B2Fe7.5Nb0.5]Fe bulk glass alloy.
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