Layer-Thickness-Dependent Strengthening-Toughening Mechanisms in Crystalline/Amorphous Nanolaminates

Crystalline/amorphous (C/A) nanolaminates offer a promising route to overcome intrinsic brittleness of bulk metallic glasses by combining high strength with enhanced plasticity. The mechanical performance of these materials is strongly governed by the crystalline-amorphous interfaces (CAIs), yet the underlying strengthening and toughening mechanisms remain poorly understood. Here, we employ large-scale molecular dynamics simulations to investigate the compressive deformation of C/A nanopillars composed of alternating equal-thickness crystalline Cu and amorphous Cu₅₀Zr₅₀ layers. The simulations reveal a nonmonotonic size effect, with the yield strength peaking at a critical layer thickness. As the layer thickness decreases, the dominant deformation mechanism shifts from shear localization in the amorphous layers to cooperative plasticity across both phases. At ultrathin layers (∼1-2 nm), shear transformation zone (STZ) activation and dislocation nucleation become dominant, enabling plastic strain to traverse interfaces and form sample-spanning shear bands. A theoretical model is proposed to explain the size-dependent strength by incorporating both amorphous and crystalline contributions. These findings provide atomic-scale insights into interface-mediated plasticity and offer guidance for designing C/A nanolaminates with superior mechanical properties.