Improved plasticity and fracture toughness in metallic glasses via surface crystallization

► A structural gradient metallic glass matrix composite material is synthesized by mechanically crystallizing the metallic glasses. ► Microstructure consists of the numerous isolated crystallite islands in the top surface layer and metallic glass matrix. ► Mechanical properties show a significant improvement in the overall plasticity and fracture toughness. ► Isolated crystallite islands effectively limit the shear bands extension, suppress the shear bands opening, and avoid the crack developing. ► Intrinsic physical origin is explored to illuminate the performance.