Intrinsic correlation between fragility and bulk modulus in metallic glasses

Abstract

A systematic study on the available data of 26 metallic glasses shows that there is an intrinsic correlation between fragility of a liquid and bulk modulus of its glass. The underlying physics can be rationalized within the formalism of potential energy landscape thermodynamics. It is surprising to find that the linear correlation between the fragility and the bulk-shear modulus ratio exists strictly at either absolute zero temperature or very high frequency. Further analyses indicate that a real flow event in bulk metallic glasses is shear dominant, and fragility is in inverse proportion to shear-induced bulk dilatation. Finally, extension of these findings to nonmetallic glasses is discussed.

How does spallation microdamage nucleate in bulk amorphous alloys under shock loading?

“…However, compared with the mean tensile stress, the shear-induced dilation in amorphous alloys is a secondary effect. 46,47 The volume dilation caused by deviatoric stress is significantly smaller than that caused by mean tensile stress, so we only consider mean tensile stress in this model.…”

Extended elastic model for flow in metallic glasses

“…Recently, it is found that the elastic moduli scaled with V m show better correlations with the thermal and mechanical properties for metallic glasses [17][18][20][21]. Thus, the characteristic volume could be an important parameter involved in the flow event in glass transition and glass.…”

“…These BMGs cover many typical alloy systems, including Zr-, Cu-, Ca-, Mg-, Ni-, Fe-, and rare earth elements Fig. 1(b) confirms that the N involved in the cooperative flow event for various metallic glasses is almost the same.Based on above scaling laws and elastic model, we propose that it is the flow activation energy density (ρ E ), not the flow activation energy itself, correlates with the elastic moduli as:The extended elastic model means that the energy per volume needed in glass transition or in STZ in metallic glass is proportional to the elastic moduli.Previous elastic models [1] suggest that the atoms or atomic groups go through pure shearing displacement which is independent of K, and the ρ E depends only on G.Recent works [18,20] and the jamming model of granular systems [22] find that both shear and dilatation are involved in the flow during glass transition and deformation.Next, we further justify the flow activation energy density ρ E relates not to G or K but both G or K. That is, the flow event relate to both shearing transformation (corresponding to volume-preserving G) and dilatation (corresponding to volume-nonpreserving K). At T g , the ∆F/T g should be the same for all glasses that is independent of Poisson's ratio or other moduli [3].…”

“…Among these models, the elastic models link the glass transition and elastic moduli of the glasses [1]. All the elastic models link the activation energy to the readily measurable instantaneous shear modulus G. In metallic glasses, the glass transition temperature (T g ) indeed shows clear correlation with the elastic moduli such as Young's modulus E and G [10][11][12][13][14][15][16][17][18].In this letter, based on the scaling laws between T g and elastic moduli in metallic glasses, we demonstrate that the V m scaled flow activation energy (∆F), that is, flow activation energy density, ρ Ε =∆F/V m , is determined by both G and K in a way of ρ Ε = (10G+K)/11. The physical origin of the extended elastic model is discussed.…”

“…Recent works [18,20] and the jamming model of granular systems [22] find that both shear and dilatation are involved in the flow during glass transition and deformation.…”