Recovering the bending ductility of the stress-relieved Fe-based amorphous alloy ribbons by cryogenic thermal cycling

Abstract

Fe-based amorphous alloys with excellent soft magnetic properties always suffer catastrophic annealing embrittlement. The soft magnetic and mechanical properties of a series of Fe84.3-xCoxSi2B13Cu0.7 (x = 0, 2, 4, 6, 8) amorphous alloy ribbons were investigated. With appropriate substitution of Co for Fe, the BS of the alloys shows a slight increase and the HC remains at a low level. From two-point bending tests, a sharp transition from ductility to brittleness can be observed upon annealing. The embrittlement can be attributed to localized shear bands due to shear bands branching during deformation. It is found that the ductile-brittle transition temperature increases slightly by applying cryogenic thermal cycling treatment to annealed ribbons, indicating that the annealing embrittlement can be improved to some extent by cryogenic thermal cycling treatment. According to nanoindentation results, the increased shear transformation zone volume is responsible for the bending ductility increment. Ultimately, a ductile Fe80.3Co4Si2B13Cu0.7 amorphous alloy ribbons with a BS of 1.68 T and a HC of 4.8 A/m were obtained by cryogenic thermal cycling treatment after annealing.