The microstructure of metallic alloys, determined by atomic arrangement and composition, is critical to material properties. Conventional dealloying processes degrade these structures by removing atoms. In contrast, the MPI-SusMat team explored how dealloying could be used to create beneficial microstructures. "We aimed to use the dealloying process to remove oxygen from the lattice structure, modulating porosity via the creation and agglomeration of oxygen vacancies," explained Dr. Shaolou Wei, Humboldt research fellow at MPI-SusMat and the study's lead author. "This method opens new pathways for designing lightweight, high-strength materials."
Central to their approach is reactive vapor-phase dealloying, a technique that employs a reactive gas atmosphere to remove oxygen atoms from the lattice. This gas, composed of ammonia, serves dual roles: it acts as a reductant through its hydrogen content and introduces nitrogen to enhance material properties. "This dual role of ammonia - removing oxygen and adding nitrogen - is a key innovation in our approach, since it assigns all atoms from both reaction partners specific roles," said Professor Dierk Raabe, managing director of MPI-SusMat and corresponding author of the study.
1. Oxide dealloying: Removes oxygen to create porosity and simultaneously reduces metal ores with hydrogen.
2. Substitutional alloying: Encourages interdiffusion between metallic elements after oxygen removal.
3. Interstitial alloying: Introduces nitrogen from the vapor phase into the metal lattice.
4. Phase transformation: Activates martensitic transformation to achieve nanoscale structuring.
This method simplifies alloy production and promotes sustainability by starting with oxides and using ammonia or industrial waste emissions as reactive gases. Replacing carbon with hydrogen as a reductant ensures the process is CO2-free, with water as the only byproduct. Thermodynamic modeling has confirmed the feasibility of this approach for metals such as iron, nickel, cobalt, and copper.
Potential applications include lightweight structural components and functional devices such as iron-nitride-based hard magnetic alloys, which could outperform rare-earth magnets. The team also envisions adapting their method to use impure industrial oxides and alternative reactive gases, reducing reliance on rare-earth materials and high-purity feedstocks. Such advancements align with global sustainability goals and could revolutionize alloy production.
By rethinking traditional metallurgical processes, the MPI-SusMat researchers have showcased how sustainability and cutting-edge microstructure engineering can drive significant advances in materials science.
This research was supported by a fellowship for Shaolou Wei from the Alexander von Humboldt Foundation, a European Advanced Research Grant awarded to Dierk Raabe, and a Cooperation Grant from the Max Planck and Fraunhofer Societies.
Research Report:Reactive vapor-phase dealloying-alloying turns oxides into sustainable bulk nano-structured alloys
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