Efficient rejuvenation of heterogeneous {[(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4}99.9Cu0.1 bulk metallic glass upon cryogenic cycling treatment

Abstract The effects of cryogenic thermal cycling on deformation behaviour and structural variation of {[(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4}99.9Cu0.1 bulk metallic glass (BMG) were studied and compared with Cu-free [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 BMG. After thermal-cycled treatment between 393 K and cryogenic temperature, the {[(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4}99.9Cu0.1 BMG obtained a plastic strain of 7.4% combined with a high yield strength of 4350 MPa. The excellent soft magnetic properties were maintained after CTC treatment. The minor addition of Cu element results in an initial nano-sized heterogeneity in the matrix, which facilitates the rejuvenation process during thermal cycling, and brings to a low optimal thermal temperature of 393 K, making the {[(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4}99.9Cu0.1 BMG more attractive in industrial application. During thermal cycling, the formation of more soft regions leads to the increase of structural heterogeneities, which is beneficial to the initiation of shear transition zones and the formation of multiple shear bands, and thus results in the enhancement of plasticity. This study links the subtle variation of specific structure with macroscopic mechanical properties, and provides a new insight of composition selection for cryogenic thermal cycling treatment.