Composition formulas of Fe–B binary amorphous alloys

Abstract

Fe–B binary alloys constitute the basis of many Fe-based metallic glasses with superior glass forming abilities and soft magnetic properties. The present work is devoted to understanding the composition rule of Fe–B binary amorphous alloys using the cluster-plus-glue-atom model and the relevant composition formula theory. According to this model, an ideal metallic glass is based on a chemical building block composed of a first-neighbor coordination polyhedral cluster plus one or three glue atoms, and the total number of valence electrons per unit formula is close to 24. For the Fe–B system, the principal cluster [B–B2Fe8], which enters into the composition formula for metallic glasses, is derived from the eutectic phase BFe2 (Al2Cu-type). This cluster, after being glued with one Fe atom, produces a cluster formula [B–B2Fe8]FeB3Fe9Fe75B25 that presents nearly 24 valence electrons. Experimental verification was then carried out, and at the anticipated composition, the crystallization temperature and glass-forming ability indicator α was the highest, indicating the best thermal stability and glass-forming ability. The crystallization behavior and structure characteristics of Fe–B binary amorphous alloys were also discussed.