Multi-principal element alloys have the potential to show excellent passivation behavior. However, the detailed compositional and crystal structure design of these alloys requires a high-throughput strategy. We used combinatorial thin-film libraries of single-phase (FeCoNi)1-x-yCrxAly alloys and compared their passivation behaviors to corresponding bulk alloys. Our results demonstrate that the detailed passivation behaviors of thin-films and bulk alloys are different which is related to both nanoscale porosity within the thin-films and grain boundary dissolution. Nevertheless, we found that comparisons made among suitably designed sets of thin-film alloys can be used to determine the best corrosion performing bulk alloy composition.
Abstract Demands for effective high‐temperature electrical conductors continue to increase with the rapid adoption of electric vehicles. However, the use of conventional copper‐based conductors is limited to relatively low temperatures due to their poor oxidation resistance and microstructural instability. Here, a highly conductive and thermally stable nickel‐graphene‐copper (NiGCu) wire that combines the advantages of graphene and its metallic components is developed. The NiGCu wire consists of a conductive copper core, an oxidation‐resistant nickel shell, and axially continuous graphene embedded between them. The experiments on 10–80 µm diameter NiGCu wires demonstrate substantial enhancements in electrical properties and thermal stability across a variety of metrics. For instance, the smallest NiGCu wires have a 61.2% higher current density limit, 307.6% higher conductivity, and an order of magnitude smaller change in resistivity compared to conventional Ni‐coated Cu counterparts after annealing at 650 °C. By performing both innovative experiments and simulations using different sizes of NiGCu wires, the diffusion coefficients of metals are quantified, for the first time to the best knowledge, through continuous graphene. These results indicate that the dramatic improvement in thermo‐electrical properties is enabled by the embedded graphene layer which reduces NiCu interdiffusion by ≈10 4 times at 550 °C and 650 °C.
Nickel-Graphene-Copper Composite Wire In article number 2214220, Wonmo Kang, and co-workers develop a highly conductive and thermally stable nickel-graphene-copper (NiGCu) wire that combines the advantages of graphene and its metallic components. Using 10 μm-diameter NiGCu wires, demonstrating 307.6% higher electrical conductivity and 61.2% higher current density limit, compared to the conventional NiCu approach, after thermal annealing at 650 °C.
Heterostructured materials (e.g., metals with multimodal microstructures) offer the promise of unprecedented functionality and performance by avoiding trade-offs between competing properties such as strength and ductility. However, methods to reproducibly synthesize heterostructured materials with explicit microstructural control are still elusive, and therefore optimizing their mechanical and functional properties via microstructural engineering is presently infeasible. Here, we describe a broadly applicable method to synthesize metallic films with precisely defined multimodal microstructures. This method enables explicit control of the size, volume fraction, and spatial connectivity of fine and coarse grains by exploiting two distinct forms of film growth (epitaxial and Volmer–Weber) simultaneously. We fabricated Cu and Fe films with bimodal and multimodal microstructures using this method and investigated their mechanical properties, which reveals a hitherto unknown breakdown in the strength–ductility synergy produced by such microstructures at small sample dimensions. Our approach enables systematic design of multimodal microstructures to tailor the mechanical properties of metallic materials and provides a platform to create functional thin films and 2D materials with prescribed phase morphologies and microstructures.
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