Large tensile plasticity induced by pronounced β-relaxation in Fe-based metallic glass via cryogenic thermal cycling

[Display omitted] •FeCoBSiNb metallic glass shows pronounced β-relaxation and large tensile plasticity after cryogenic thermal cycling.•Increase of structural heterogeneity leads to pronounced β-relaxation and enhanced tensile plasticity.•β-relaxation exhibits separate peaks with diverse cycling temperatures, which is resulted from different sizes/types of shear transformation zones. The effects of cryogenic thermal cycling (CTC) treatment on tensile plasticity and structure change of [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 metallic glass (MG) ribbons were systematically investigated. Pronounced β-relaxation peaks locating at 643 and 693 K were observed after CTC treatment with diverse thermal temperatures. Specifically, the CTC treated samples exhibiting most remarkable β-relaxation showed tensile plastic strain of 5.2% at 643 K and 4% at 693 K, while the as-quenched sample only showed tensile plastic strain of 3% at 643 K and 2.1% at 693 K. The pronounced β-relaxation and enhanced tensile plasticity are considered to be originated from the increased structural heterogeneity. The separate β-relaxation peaks result from the different sizes/types of shear transformation zones induced by oscillatory (rejuvenation-relaxation) behavior during thermal cycling. Our results indicate that the CTC treatment has a significant impact on the energy states and structural heterogeneity, which makes it a powerful means to modify the mechanical properties of MGs.