Dynamic fracture instability of tough bulk metallic glass

Abstract

We report the observations of a clear fractographic evolution from vein pattern, dimple structure, and then to periodic corrugation structure, followed by microbranching pattern, along the crack propagation direction in the dynamic fracture of a tough Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 ͑Vit.1͒ bulk metallic glass ͑BMGs͒ under high-velocity plate impact. A model based on fracture surface energy dissipation and void growth is proposed to characterize this fracture pattern transition. We find that once the dynamic crack propagation velocity reaches a critical fraction of Rayleigh wave speed, the crack instability occurs; hence, crack microbranching goes ahead. Furthermore, the correlation between the critical velocity of amorphous materials and their intrinsic strength such as Young's modulus is uncovered. The results may shed new insight into dynamic fracture instability for BMGs.

Cryogenic-temperature-induced transition from shear to dilatational failure in metallic glasses

“…5e and f shows the transition of dimple patterns to nanoscale periodic corrugations. This transition is usually due to the acceleration of crack propagation in the final stage [45]. It demonstrates that the two patterns have an identical nature of cavitation, as revealed previously [14,19,46].…”

Nanoscale periodic corrugation to dimple transition due to “beat” in a bulk metallic glass

“…In this case, atomic cluster in the fracture process zone moves via shear transformation zones (STZs) (see the inset in Fig. 1a), introduced by Argon [28], through which vein patterns or dimples can finally form due to the fluid meniscus instability [19,20,[24][25][26]. If the converse is true, i.e.…”

“…If the size of the fracture process zone ahead of crack tip, which can be measured by the curvature radius R of the crack tip, is greater than the critical wavelength k c of the fluid meniscus instability [19,20], a fracture with some softening is possible [24][25][26][27], as illustrated in Figure 1(a). That relation reads [20,25] …”

“…It is important to point out that the crack radius R determining the size of fracture patterns strongly depends on strain rate and ambient temperature. Therefore, even for the same BMG system, it can exhibit the DTB transition phenomenon with varying strain rates [4,21,25,26] or temperatures [5]. The underlying mechanism is the transition between STZs and TTZs ahead of the crack tip.…”

“…Recently, similar dimples and much finer nanoscale periodic corrugations (NPCs) have been found on optically mirror-reflecting fracture surfaces of some ideally or less brittle BMGs [2,4,[22][23][24]. In order to reveal the fracture mechanism, we have performed a systematic study on the fracture patterns of a typical tough Zr 41.2 Ti 13.8 Cu 10 Ni 12.5 Be 22.5 (Vit 1) BMG under compression, tension and high-velocity plate impact over a wide range of strain rates from $10 À4 to 10 6 s À1 [25,26]. It has been shown that this tough Vit 1 BMG can also exhibit fine dimples at the 100 nm scale and even NPCs on dynamic mode I fracture surfaces, in addition to conventional vein patterns; these fracture morphologies can interchange with each other with changes in cracking speed and fracture mode.…”