COMPOSITION DESIGN AND OPTIMIZATION OF Fe-B-Si-Nb BULK AMORPHOUS ALLOYS

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 similar to 1.2) are derived. Copper mold casting experiments revealed that bulk glass alloys with a critical diameter (d(c)) exceeding 1.0 mm are readily obtained with the Nb content range of x=0.2 similar to 1.2, the largest d(c) (about 2.5 mm) appears in the vicinity of x=0.4 similar to 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 d(c)=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 (B-s=1.14 similar to 1.46 T) and low coercive forces (H-c=1.6 similar to 6.7 A/m) is found in the [Si-B(2)Fes Nb]Fe (x=0.2 similar to 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.