On the impact toughness of amorphous/crystalline metallic laminates

Abstract

The creation of amorphous/crystalline (A/C) laminated structures offers a promising approach towards the production of damage-tolerant A/C metallic materials. However, constraints in fabrication techniques have resulted in limited explorations into the toughening behavior of bulk A/C laminates. This study scrutinizes the impact toughness of macroscale A/C Ni–P/Ni laminates through instrumented Charpy impact testing. The findings reveal that the thickness of the amorphous Ni–P layer significantly influences the impact toughness of A/C Ni–P/Ni laminates. A/C Ni–P/Ni laminates possessing thin Ni–P layers (1 or 4 μm) demonstrated high impact energy, which was comparable to the monolithic coarse-grained (CG) structure; however, the impact energy decreased with the increasing Ni–P layers thickness. Microstructural characterization of the crack-path profile disclosed that the desired impact toughness in the A/C Ni–P/Ni laminate with a thin Ni–P layer is primarily due to intrinsic toughening induced by plastic deformation ahead of the crack tip, and extrinsic toughening afforded by interface delamination. As the Ni–P layer thickens, brittle interface delamination emerges as the dominant extrinsic toughening source to resist fracture, thereby rendering the A/C Ni–P/Ni laminate vulnerable to impact loading. This work not only elucidates the dependence of toughening mechanism on the Ni–P layer thickness in A/C Ni–P/Ni laminates but also proposes an effective strategy for designing damage-tolerant metallic materials subject to impact loading by incorporating thin, brittle amorphous and thick, ductile crystalline materials to create laminated structures.