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 Cu 50 Zr 50 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.