Plasticity induced by nanoparticle dispersions in bulk metallic glasses

Nucleation of shear bands in amorphous alloys

“…The specific defects have not been identified here, but it seems likely that they are local nanoscale heterogeneities that promote STZ activity. Indeed, some estimates of the relative STZ size and equivalent number of atoms have been calculated, but the range of values is broad enough from 10 to hundreds of atoms (8,44,45) that it could represent more than one type; a recent report indicates that a fine structure exists within this range (45). Further evaluation of the models is necessary, but the key finding of a bimodal distribution of nucleation sites may provide guidance to promote nucleation to enhance shear band activity and ductile behavior.…”

“…The onset of shear bands in metallic glasses represents initial plastic yielding and induces a highly localized plastic flow that limits ductility and is responsible for strain softening (4,5). Because shear bands directly determine the capability of an amorphous phase to sustain plastic flow and exhibit ductile behavior, there have been numerous studies on the propagation of shear bands to promote shear band branching and additional nucleation to achieve useful ductility (6)(7)(8)(9). On a microscopic scale, the initiation of shear bands in MGs is considered to be controlled by the activation of a shear transformation zone (STZ) (10,11) that represents a localized atomic arrangement.…”

Mechanical Properties and Deformation Behavior of Bulk Metallic Glasses

“…The blockage of the crack-tip area by nanoparticles stabilizing plastic deformation was observed in Cu 50 Zr 50 as well as in the Zr 65 Al 7.5 Ni 10 Pd 17.5 glassy alloys [89]. Moreover, the compressive room-temperature stress-strain curves of the Zr 65 Al 7.5 Ni 10 Cu 17.5 and Zr 65 Al 7.5 Ni 10 Pd 17.5 bulk metallic glassy alloys revealed significantly different plasticity of these alloys, though both of the alloys possess a glassy structure [90].…”

On the Modelling of the Transient Flow Behavior of Metallic Glasses: Analogy with Portevin-Le Chatelier Effect

“…Several intrinsic and extrinsic factors have been suggested to cause the arrest of the shear banding operation. We have experimentally established that the in situ nanocrystallization within the shear bands can offer a "self-locking effect" and increases the strength of shear regions preventing further propagation of shear bands [10][11][12]. Few authors have considered a type of relaxation mechanism able to increase the resistance to the shear bands motion [13].…”