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A New Alloy Material That Overcomes Hydrogen Embrittlement Through a “Soft Outside, Strong Inside” Strategy

From left: Professor Hyoung Seop Kim of the Graduate Institute of Ferrous & Eco Materials Technology (GIFT) and the Department of Materials Science and Engineering at POSTECH, and Rae-eon Kim, Ph.D. student in the Department of Eco Materials Science at POSTECH. Courtesy of POSTECH.

A new materials design strategy has been proposed to overcome the hydrogen embrittlement of high-strength metals, one of the major challenges in realizing a hydrogen-based economy.

POSTECH announced on the 27th that a research team led by Professor Hyoung Seop Kim of GIFT and the Department of Materials Science and Engineering has developed a high-strength alloy design strategy that effectively overcomes hydrogen embrittlement. The findings were published online on March 6 (local time) in the international journal Corrosion Science.

Hydrogen embrittlement refers to a phenomenon in which hydrogen that penetrates a metal accumulates within its internal structure, reducing ductility and triggering cracks. High-strength metals are generally more susceptible to hydrogen embrittlement, making it a critical challenge in developing structural materials for use in hydrogen environments.

This presents a dilemma for the development of hydrogen storage tanks and pipeline infrastructure: metals must be both strong and highly resistant to hydrogen.

Metallic materials are typically designed with a hard surface and a softer interior. 

The research team reversed this conventional structure by developing a high-entropy alloy with a soft but hydrogen-resistant recrystallized microstructure at the surface and a cold-rolled microstructure in the interior to enhance strength.

This represents a “reverse-gradient” structural design strategy that turns the conventional approach upside down. 

High-entropy alloys are materials designed by incorporating multiple elements simultaneously to increase configurational disorder, or entropy.

The key concept of the design is a hydrogen-resistant surface layer that withstands the external environment and prevents hydrogen from penetrating into the interior through structural shielding, without requiring additional coatings or protective layers.

In other words, the material is designed to trap or disperse hydrogen simply through the strategic arrangement of its internal microstructures.

The combination of the two distinct microstructures also improved ductility, the ability of a material to undergo deformation without fracturing, as the two regions interacted and deformed together.

The newly developed alloy demonstrated a yield strength 2.4 times higher than that of a conventionally heat-treated alloy. Yield strength refers to the minimum stress at which permanent deformation begins.

The findings are significant in demonstrating that hydrogen embrittlement can be mitigated without relying on surface coatings or complicated post-processing techniques.

The technology is expected to have applications ranging from hydrogen infrastructure to the development of high-strength structural materials for extreme environments.

Rae-eon Kim, a Ph.D. student in the Department of Eco Materials Science at POSTECH and the first author of the paper, explained, “We confirmed that the reverse-gradient design, inspired by naturally occurring hierarchical structures, can overcome not only the trade-off between strength and ductility but also environmental embrittlement issues such as hydrogen embrittlement.”

Professor Kim stated, “Beyond conventional approaches that rely on surface coatings to address hydrogen embrittlement, we have proposed a new design principle in which the microstructure itself actively shields the material from hydrogen. This approach has broad potential for the design of next-generation alloys for hydrogen storage and transportation.”