Development and characterization of new Co-Fe-Hf-B bulk metallic glass with high thermal stability and superior soft magnetic performance

Cobalt-based metallic glasses have stimulated widespread interest due to their excellent mechanical properties and soft magnetic behavior. In the present work, a new Co51Fe15Hf6.5B27.5 glassy alloy was designed based on the ternary eutectic Co66Hf6.5B27.5 composition and its microstructure, thermal behavior and magnetic properties were examined. Partial substitution of Co with Fe in the new alloy systematically changes the crystallization behavior, enhances the fraction of complex (Co,Fe)(21)Hf2B6 phase upon crystallization and increases the extension of the supercooled liquid region from 26 K to 48 K. The improved thermal stability is in line with an increased activation energy of crystallization from 523 +/- 20 kJ/mol for the Co66Hf6.5B27.5 glass to 573 +/- 20 kJ/mol, corresponding to the Co51Fe15Hf6.5B27.5 glass. Magnetic studies revealed that the addition of Fe noticeably increases the saturation magnetization, Curie temperature, and slightly increases the coercive force from 19 A m(2)/kg to 57 A m(2)/kg, 315 K -515 K and 0.5 A/m to 1.5 A/m, respectively. It was found that the Co51Fe15Hf6.5B27.5 glassy ribbons exhibit a high resistance against milling-induced crystallization under cryogenic condition. The prepared cryomilled glassy particles show adequate thermal stability and thermoplastic forming ability for hot consolidation into a high density (96%) bulk metallic glass (BMG) with 10 mm diameter. The Co51Fe15Hf6.5B27.5 BMG exhibits a saturation magnetization of 57 A m(2)/kg, a Curie temperature of 527 K and a very low coercivity of 7 A/m, indicating its superior soft magnetic performance compared to most Co/Fe-based BMGs fabricated via powder metallurgy techniques. The evolution of microstructure, thermal behavior and magnetic properties upon cryomilling, hot consolidation and subsequent annealing was discussed. (C) 2020 Elsevier B.V. All rights reserved.