Abstract
Metallic glass composites with shape memory crystals show enhanced plasticity and work-hardening capability. We investigate the influence of various critical structural aspects such as, the density of crystalline precipitates, their distribution and size, and the structural features and intrinsic properties of the phase on the deformation behavior of metallic amorphous CuZr composites with B2 CuZr inclusions using molecular dynamics simulations. We find that a low density of small B2 inclusions with spacing smaller than the critical shear band length controls the formation and distribution of plastic zones in the composite and hinders the formation of critical shear bands. When the free path for shearing allows the formation of mature shear bands a high volume fraction of large B2 precipitates is necessary to stabilize the shear flow and avoid runaway instability. Additionally, we also investigate the deformation mechanism of composites with pure copper crystals for comparison, in order to understand the superior mechanical properties of metallic glass composites with shape memory crystals in more detail. The complex and competing mechanisms of deformation occurring in shape memory metallic glass composites allow this class of materials to sustain large tensile deformation, even though only a low-volume fraction of crystalline inclusions is present.
Highlights
Improving the plastic deformability of metallic glasses (MGs) is the key to the extensive use of these attractive materials in structural and functional applications
The free path for shearing in this MG composite is long enough to form critical shear bands (≈23 nm) these planar defects are confined by the crystalline precipitates and the strain is homogeneously distributed in the whole composite on different slip planes carrying plastic deformation
To emphasize the superior mechanical properties of MG composites with shape memory crystals we compare their deformation mechanism to the one of composites with nanocrystalline inclusions which deform via dislocation activity
Summary
Improving the plastic deformability of metallic glasses (MGs) is the key to the extensive use of these attractive materials in structural and functional applications. The deformation-induced martensitic phase transformation of B2 to B190 provides a high density of interfaces of phases and twins [8] This hardens the crystalline phase and hinders shear bands to penetrate through the precipitates [18,23,24]. An autocatalytic chain-type deformation mechanism of MG composites was found for such composites: the martensitic transformation leads to shear band formation and likewise the stress at the shear band tip induces martensitic transformation in the shape memory crystal, promoting a heterogeneous distribution of strain into the glassy matrix [25,26]. The complex and competing mechanisms of deformation occurring in the glassy matrix and B2 inclusions allow amorphous-crystalline nanolaminates with low-volume fraction of B2 phase (below 45 vol.%) to exhibit large tensile ductility and nearly ideal plastic flow behavior. The superior mechanical properties of MG composites with shape memory crystals are highlighted by comparing their deformation mechanisms to those observed for composites with nanocrystalline inclusions which deform via dislocation activity [27,28]
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