Self-toughening crystalline Cu/amorphous Cu-Zr nanolaminates: Deformation-induced devitrification

How to defeat the conflict of strength vs. toughness and achieve unprecedented levels of damage tolerance within either metallic crystalline or metallic glassy family is a great challenge for designing structural materials. The combination of glassy with crystalline nanolayers can manifest extraordinarily high toughness, i.e. superior strength in conjunction with high ductility, when the constituent layers approach a critical internal feature size. Three-point bending and uniaxial microcompression tests were performed on Cu/Cu-Zr crystalline/amorphous nanolaminates (C/ANLs) with equal layer thicknesses ∼50 nm to investigate their toughening behaviors. The dislocations absorbed by the amorphous phase not only render defect-free nanocrystals, but also create nanocrystallites in glassy nanolayers. It is revealed that the Cu/Cu-Zr C/ANLs self-toughen via the combination of the extrinsic shielding effect of crystalline/amorphous interfaces on a crack growth accommodated by an extensive shear-band sliding process and the intrinsic deformation-induced devitrification mechanism associated with the brittle-to-ductile transition of glassy nanolayers. The findings indicate that the high damage tolerance potentially accessible to glassy materials can extend beyond the benchmark ranges towards levels previously inaccessible to metallic crystalline-amorphous composites.