Softening and good ductility for nanocrystal-dispersed amorphous Fe-Co-B alloys with high saturation magnetization above 1.7 T

Fe80-xCo20Bx (x = 12-15 at%) alloy ribbons consisting of single bcc phase (12%B), amorphous plus bcc-Fe(Co) mixed phases (13%B) and amorphous single phase (14%B and 15%B) were synthesized by the melt-spinning technique. It is noticed that all the alloy ribbons containing amorphous phase exhibit good bending ductility in the as-spun state and even after annealing which leads to the precipitation of nanoscale bcc-Fe(Co) phase. The amorphous plus bcc-Fe(Co) phase alloys with lower hardness exhibited a number of microcracks in the region near the hardness indentation trace, in addition to distinct slip step markings. The decrease in hardness and the maintenance of ductility in the nanocrystalline state are interpreted to originate from microcrack-induced softening phenomenon. The nanocrystalline alloys also exhibit good soft magnetic properties with high saturation magnetization above 1.7 T in combination with low coercivity of about 20 A/m. The good bending ductility as well as the microcrack-induced softening for the amorphous alloys including nanoscale bcc-Fe(Co) phase is believed to be the first evidence in the long development history of Fe-based nanocrystalline soft magnetic alloys. The finding of the ductile Fe-based nanocrystalline alloys with high saturation magnetization is encouraging for further extension of nanocrystalline magnetic materials. (C) 2015 Elsevier B.V. All rights reserved.