Signature of local stress states in the deformation behavior of metallic glasses

Abstract

The design of ductile heterogeneous metallic glasses (MGs) with enhanced deformability by purposely controlling the shear-band dynamics via modulation of the atomic-scale structures and local stress states remains a significant challenge. Here, we correlate the changes in the local atomic structure when cooling to cryogenic temperature with the observed improved shear stability. The enhanced atomic-level structural and elastic heterogeneities related to the nonaffine thermal contraction of the short-range order (SRO) and medium-range order (MRO) change the characteristics of the activation process of the shear transformation zones (STZs). The experimental observations corroborated by Eshelby inclusion analysis and molecular dynamics simulations disclose the correlation between the structural fluctuations and the change in the stress field around the STZ. The variations in the inclination axes of the STZs alter their percolation mechanism, affect the shear-band dynamics and kinetics, and consequently delay shear failure. These results expand the understanding of the correlation between the atomic-level structure and elementary plastic events in monolithic MGs and thereby pave the way for the design of new ductile metallic alloys.

Strong yet Ductile High Entropy Alloy Derived Nanostructured Cermet

“…This behavior suggests that the amorphous interphase is fluid-like, which can quickly relax local high stresses . We note that the atomic stress fluctuates in the amorphous interphase, which may be attributed to the structural heterogeneity inherent to glasses . Aside from the atomic stress in the loading direction, we also calculated the atomic stress in the amorphous interphase in the y direction.…”

“…31 We note that the atomic stress fluctuates in the amorphous interphase, which may be attributed to the structural heterogeneity inherent to glasses. 40 Aside from the atomic stress in the loading direction, we also calculated the atomic stress in the amorphous interphase in the y direction. As shown in Figure 5g, there are large compressive atomic stresses, indicating strong elastic confinements against the flowing amorphous interphase from sideways when the model cermet is pulled.…”

Cryo-Casting for Controlled Decomposition of Cu–Zr–Al Bulk Metallic Glass into Nanomaterials: Implications for Design Optimization

“…Our group has recently proposed that an increased degree of heterogeneity (i.e., more distinct hard and soft zones in terms of composition, Table ) generates a complex stress field around STZs, eventually turning uniaxial to the multiaxial complex stress field. Hence, the STZ percolation process and the formation of critical shear bands slow down, which delays the shear failure of MGs . Relatively closer compositions of Cu- and Zr-rich regions possibly establish the stress transfer between each other, hence yielding the highest ε pl and σ f among three T mold samples.…”

“…Hence, the STZ percolation process and the formation of critical shear bands slow down, which delays the shear failure of MGs. 47 Relatively closer compositions of Cu-and Zr-rich regions possibly establish the stress transfer between each other, hence yielding the highest ε pl and σ f among three T mold samples. The secondary phase separation in the M298K sample decreases the distances between Cu-and Zr-rich regions down to 1−2 nm.…”

High strain rate in situ micropillar compression of a Zr-based metallic glass

“…In metallic glasses, the atomic-scale ordering known as short-and medium-range order (SRO and MRO) play a determining role over their properties [19,20] for both homogeneous and inhomogeneous deformation modes [21]. Variations in the local clustering of atoms lead to changes in shear band dynamics and density [22]; local soft spots and/or high medium range order in the structure act as sites with a high propensity for shear transformation zone (STZ) activation [20,23], with clear consequences on the transition to plastic flow during material deformation [24]. Changing the local chemical structure can also affect the response at high strain rates, as demonstrated by Inoue and co-workers for Zr-Cu-Al amorphous alloys with various amounts of Ni additions via Charpy impact testing [25], while the degree of hybridised bonding has also been shown to be linked to the fracture toughness of metallic glasses [26].…”