Strong and tough materials have been crucial for ensuring the survival of the human race since its beginnings thousands of years ago. Today, extreme applications such as those found in aircraft turbines and nuclear reactors demand ever stronger and deformable metals. One candidate for filling this role is nanostructured alloys, which are made up of nanoscale crystallites. These materials often achieve near-theoretical strengths but frequently suffer from limited ductility, unlike alloys with coarser crystallite size. One way to engineer strength and deformability into nanostructured metals is to control interface structures within — the high interface content associated with nanoscale grains makes this strategy viable. We use bimetallic Cu/Nb nanolaminates (hereafter Cu/Nb) as a model system to study the influence of interface structure on mechanical properties in nanocrystalline alloys. While nanolaminates with chemically abrupt 2D interfaces have demonstrated impressive strength and deformability, their ductility is limited due to shear banding. Here, a thin region of the material deforms more than its surroundings, softening the material and causing failure. To mitigate shear banding, we introduce thick 3D interfaces that are chemically, crystallographically, and structurally heterogeneous in all spatial dimensions to heterophase boundaries in Cu/Nb to form 3D Cu/Nb. This material has increased strength and deformability compared to 2D interface counterparts (2D Cu/Nb) under in situ SEM micropillar compression, demonstrating that control of bimaterial interface structure enhances stability under extreme mechanical loading and may be central to designing high-performing materials that can survive extreme conditions.
