Abstract
We synthesized CuZr/Cu multilayers and performed nanoindentation testing to explore the dependence of plastic deformation modes on the thickness of CuZr layers. The Cu layers were 18 nm thick and the CuZr layers varied in thickness from 4 nm to 100 nm. We observed continuous plastic co-deformation in the 4 nm and 10 nm CuZr − 18 nm Cu multilayers and plastic-induced shear instability in thick CuZr layers (>20 nm). The plastic co-deformation is ascribed to the nucleation and interaction of shear transformation zones in CuZr layers at the adjacent interfaces, while the shear instability is associated with the nucleation and propagation of shear bands in CuZr layers. Shear bands are initialized in the CuZr layers due to the accumulated glide dislocations along CuZr-Cu interfaces, and propagate into adjacent Cu layers via slips on {111} plane non-parallel to the interface. Due to crystallographic constraint of the Cu layers, shear bands are approximately parallel to {111} plane in the Cu layer.
Highlights
Amorphous metallic alloys or metallic glasses (MGs) have attracted much attention due to their excellent physical, chemical, and mechanical properties[1,2]
Microstructural characterization of CuZr/Cu multilayers using scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD) reveals several features as shown in Fig. 1 and Figure S1 in the Supplementary: (i) CuZr/Cu composites have continuously layered structure; (ii) Cu grains are of single crystal across the layer thickness and the grain size is comparable to the layer thickness; and (iii) there is no apparent columnar structure
Our experiments so far revealed a profound size effect on plastic deformation of CuZr/Cu multilayers, i.e., CuZr/ Cu multilayers plastically co-deform without the formation of shear bands when the CuZr layer thickness is less than 20 nm, but they deform associated with the formation and propagation of shear bands when the CuZr layer is thicker than 20 nm
Summary
Amorphous metallic alloys or metallic glasses (MGs) have attracted much attention due to their excellent physical, chemical, and mechanical properties[1,2]. Under compression, deflected shear bands with a wavy shape are generated in MGs samples with small dimensions in the directions perpendicular to the applied load, suppressing rapid extension of shear bands[9,10] These studies suggest that plasticity enhancement in MGs can be achieved by tuning MGs compositions or microstructures that tailor mechanical characteristics of formation, extension and growth of shear bands in MGs. Metal/MGs layered composites have been fabricated[11,12,13,14] because of the potential enhancement of mechanical properties (strength and ductility) like what has been observed in crystalline metal/metal and metal/ceramics nanolayered multilayers[15,16,17,18,19,20,21,22,23,24,25]. Hardness obtained within a certain depth range of 4 ~ 6 times bilayer thickness, which is smaller than 1/5 of the total thickness of the multilayers
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