Transformation-mediated and relaxation-assisted macroscopic tensile plasticity with strain-hardening in metallic glass
Fan Hu, Qiang Luo, Mingjuan Cai, Qianqian Wang, Jingxian Cui, Yusha Luo, Bo Sun, Zhijun Guo, Baolong Shen
Abstract
Metallic glasses (MGs) possess the merits of high strength and a large elastic limit. However, they suffer from little tensile ductility in the inhomogeneous deformation regime due to strain softening and shear localization. In this work, we report a substantial increase in tensile plastic strain (εp) from 2.8% to 10% in a Fe-based metallic glass (MG) via non-affine thermal strain (NTS), accompanied by a significant intensity enhancement and a considerable decrease in activation energy (32%) of the β-relaxation. Notably, pronounced strain hardening is observed during tension. These extraordinary tensile properties are structurally attributed to the NTS-promoted formation of a chemical-fluctuation-mediated network structure consisting of interconnected Fe-rich medium-range orders (MROs) and surrounding metalloid-rich clusters, as well as the subsequent temperature and stress-induced unique evolution of the multiscale structural heterogeneities. Specifically, the stress-induced unique MRO formation, α-Fe nanocrystallization, and the irreversible relaxation-induced structural ordering jointly interact with shear banding to transform strain softening into hardening, leading to excellent ductility. These findings demonstrate that simultaneous relaxation-assisted and transformation-mediated deformation stabilizes the inhomogeneous plastic flow under tension, overcoming the ductility bottleneck of MGs. Metallic glasses can break ductility bottlenecks: 10% tensile plasticity with strain-hardening emerges from a synergy between relaxation-assisted and transformation-mediated deformation mechanisms, overcoming a long-standing challenge in metallic glasses.