Balancing strength, hardness and ductility of Cu₆₄Zr₃₆ nanoglasses via embedded nanocrystals

Superplasticity can be achieved in nanoglasses but at the expense of strength, and such a loss can be mitigated via embedding stronger nanocrystals, i.e., forming nanoglass/nanocrystal composites. As an illustrative case, we investigate plastic deformation of Cu₆₄Zr₃₆ nanoglass/nanocrystalline Cu composites during uniaxial tension and nanoindentation tests with molecular dynamics simulations. With an increasing fraction of nanocrystalline grains, the tensile strength of the composite is enhanced, while its ductility decreases. The dominant interface type changes from a glass-glass interface to glass-crystal interface to grain boundary, corresponding to a failure mode transition from superplastic flow to shear banding to brittle intercrystal fracture, respectively. Accordingly, the indentation hardness increases continuously and strain localization beneath the indenter is more and more severe. For an appropriate fraction of nanocrystalline grains, a good balance among strength, hardness and ductility can be realized, which is useful for the synthesis of novel nanograined glass/crystalline composites with high strength, high hardness and superior ductility.