Yield point of metallic glass

Structure in sheared supercooled liquids: Dynamical rearrangements of an effective system of icosahedra

“…Shear banding is the separation of a sheared system into two regions of different viscosity and internal structure [48,49]. Some suggested mechanisms for the formation of shear bands are via the percolation of STZs [39,50] or from high stress localization in inherent defects or voids in the system [51]. Shearing has also been shown to increase the energy of soft glassy materials, called rejuvenation [52,53], and varying the shear rate can yield systems with different effective temperatures [54][55][56].…”

Ductile crystalline–amorphous nanolaminates

“…The large defect cluster that evolves out of the amorphous phase (embryonic shear band), which could eventually fail the whole amorphous material, may have been stopped by the nanocrystalline layers before it reaches maturity (18). Similarly, dislocation structures and geometric incompatibilities, which could localize in nanocrystalline grains and GBs (causing large stress concentrations and perpetuating themselves by jumping from grains to grains), may have been disrupted and dissolved by the amorphous layers.…”

“…As dislocation motion in high-strength crystalline materials becomes increasingly difficult (11), the ductility, i.e., the ability of a material to change shape without catastrophic failure, is often reduced dramatically (6,7). In bulk metallic glasses, plastic deformation is not enabled by dislocations (12)(13)(14)(15)(16)(17)(18)(19)(20)(21) but rather by clusters of atoms that undergo cooperative shear displacements [shear transformation zones (STZs)] (16); in the extreme limit of homogeneous-toinhomogeneous flow transition, shear bands of nanoscale width form (17,(19)(20)(21). The formation of such shear bands causes large strain softening and abrupt rupture of the metallic glasses.…”

“…Our simulations have shown that ACIs clearly act as natural sinks of dislocations, absorbing the dislocation content in the nanocrystalline copper after plastic work has been accomplished (32). To characterize the atomic-scale physics occurring in the metallic glass when dislocations are absorbed, we quantitatively compute the atomistic inelastic strain (18) in reference to a configuration before dislocation activities (Fig. 3 C and D; the atoms with the inelastic strains Ͻ6% are not shown).…”

“…Our room-temperature rolling experiments further indicate that the plastic flow of the nanoscale metallic glass layers remains uniform, even when the individual layer thickness reduction is 50%. The lack of shear banding in the nanoscale metallic glass layers may be understood in terms of the aged-rejuvenation-glue-liquid shear band model (18). It predicts that the size of the stressed metallic glass region must exceed an incubation length scale L inc in order for STZs to develop into mature shear bands:…”