Scientists transform dealloying into durable lightweight alloy design

Researchers at the Max Planck Institute for Sustainable Materials (MPI-SusMat) have transformed dealloying, traditionally considered a corrosive and destructive process, into a revolutionary method for creating lightweight, high-strength alloys. By combining dealloying and alloying in a single step, the team developed nanoporous martensitic alloys using reactive gases like ammonia, which simultaneously remove oxygen and introduce nitrogen into the material’s structure.

This sustainable approach, published in Scientific advancesoffers energy-efficient alloy production with potential applications ranging from lightweight components to advanced functional materials, such as alternatives to rare earth magnets.

Alloying, the art of mixing metals with other elements, has long been a cornerstone of materials science and metallurgy, creating materials with customized properties. In contrast, dealloying is primarily known as a corrosive process that degrades materials over time by selectively removing elements, thereby weakening their structure. Today, researchers have transformed these two seemingly opposing processes into an innovative concept of harmonic synthesis.

The microstructure of metal alloys is defined by the arrangement of atoms within a lattice, with their position and chemical composition being essential to the properties of the material. Traditional dealloying naturally removes atoms from this network, causing degradation. But the MPI-SusMat team asked a revolutionary question: what if we could harness dealloying to create beneficial microstructures?

“We aimed to use the dealloying process to remove oxygen from the network structure, modulating porosity via the creation and agglomeration of oxygen vacancies,” explains Dr Shaolou Wei, Humboldt researcher at MPI-SusMat and first author of the publication. “This method opens new avenues for designing lightweight, high-strength materials.”

At the heart of their approach is reactive vapor dealloying, a technique that removes oxygen atoms from the lattice structure using a reactive gas atmosphere. In this process, the atmosphere “draws in” oxygen, selectively extracting it from the host network. Thus, the atmosphere consists of ammonia, which acts both as a reducer (via its hydrogen content) and as an interstitial nitrogen donor, filling empty spaces in the network to improve material properties.

“This dual role of ammonia (removal of oxygen and addition of nitrogen) constitutes a key innovation in our approach, because it assigns all atoms of the two reaction partners specific roles,” says Professor Dierk Raabe , managing director of MPI-SusMat and corresponding author of the study. .

Four crucial metallurgical processes in one step

The team’s breakthrough lies in the integration of four crucial metallurgical processes into a single reactor stage:

1. Oxide Dealloying: Removing oxygen from the lattice to create excessive porosity while simultaneously reducing metal ores with hydrogen.
2. Substitutional alloy: encourages solid-state interdiffusion between metallic elements upon or after complete removal of oxygen.
3. Interstitial alloying: introduction of nitrogen from the vapor phase into the host network of won metals.
4. Phase transformation: activation of thermally induced martensitic transformation, the most viable route for nanostructuring.

This synthesis strategy not only simplifies alloy production, but also offers a sustainable approach by using oxides as raw materials and reactive gases such as ammonia or even waste emissions from industrial processes. By using hydrogen as a reducing agent and energy carrier instead of carbon, the entire dealloying-alloying process is CO₂-free and the only byproduct is water. Thermodynamic modeling demonstrates the feasibility of this technique for metals such as iron, nickel, cobalt and copper.

Lightweight, durable design through microstructural engineering

The resulting nanostructured porous martensitic alloys are lighter and stronger, thanks to precise control of the microstructure from the millimeter down to the atomic scale. Traditionally, achieving such porosity required time- and energy-intensive processes. In contrast, the new strategy accelerates the formation of porosity while allowing the simultaneous introduction of interstitial elements like nitrogen that improve the strength and functionality of the material.

Future applications could range from lightweight structural components to functional devices such as hard magnetic alloys based on iron nitride, which could outperform rare earth magnets in performance. Looking ahead, the researchers plan to expand their approach to the use of impure industrial oxides and alternative reactive gases. This could revolutionize alloy production by reducing reliance on rare earth materials and high-purity raw materials, thereby aligning with global sustainability goals.

Through this innovative dealloying-alloying strategy, the MPI-SusMat team demonstrated how rethinking traditional processes can generate transformative advances in materials science. By combining durability and cutting-edge microstructural engineering, they are paving the way for a new era of alloy design.