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From left: Professor Hyoung Seop Kim of POSTECH’s Department of Eco-Friendly Materials and Department of Materials Science and Engineering; Raeeon Kim, Ph.D. student in the Department of Eco-Friendly Materials; and Jumi Choi, master’s student. Courtesy of POSTECH.

A Korean research team has proposed a new approach to addressing the long-standing dilemma of hydrogen embrittlement, in which increasing the strength of metals can make them more vulnerable to hydrogen penetration and subsequent degradation.

The technology is expected to offer a new solution for designing metallic structures used in hydrogen storage and transportation infrastructure, as well as cryogenic equipment.

A research team led by Professor Hyoung Seop Kim of POSTECH’s Department of Eco-Friendly Materials and Department of Materials Science and Engineering has successfully enhanced both the strength and resistance to hydrogen embrittlement of metals by combining cryogenic processing with heat treatment, POSTECH announced on August 31.

The findings were published online on December 1 last year in the international journal Materials Research Letters.

As hydrogen gains attention as a next-generation clean energy source for achieving carbon neutrality, ensuring the safety and durability of hydrogen infrastructure, including storage vessels and pipelines, has become increasingly important.

However, a major challenge is that increasing the strength of metallic materials can also make them more susceptible to hydrogen embrittlement.

Hydrogen embrittlement occurs when hydrogen atoms penetrate a metal and weaken its structure, potentially leading to cracks and failure.

Conventionally, microscopic defects are intentionally introduced into metals to prevent the layers of metal atoms from slipping past one another, thereby increasing strength. 

However, these microscopic spaces can also provide pathways for hydrogen to penetrate and become sites where cracks initiate.

The research team focused on a structure known as a “nanotwin.” Nanotwins are symmetrical structures formed within a crystal at intervals of just a few nanometers, where 1 nanometer is one-billionth of a meter.

Nanotwins can increase the strength of metals by effectively blocking the movement of dislocations while preventing hydrogen from accumulating. 

However, a key challenge has been that the process of creating nanotwins can simultaneously introduce defects that make the material vulnerable to hydrogen embrittlement.

The researchers applied mechanical stress to a high-entropy alloy at an extremely low temperature of −196°C, generating a dense network of nanotwins. 

They then heated the material to approximately 500°C. As a result, the nanotwins that contribute to the material’s strength remained, while defects responsible for hydrogen embrittlement were significantly reduced.

High-entropy alloys are materials composed of multiple elements in relatively high concentrations, increasing the degree of disorder, or entropy, within the material.

The newly developed alloy exhibited a 2.2-fold increase in yield strength compared with conventional alloys, while the depth of the surface layer damaged by hydrogen penetration and embrittlement was significantly reduced.

Yield strength refers to the minimum stress at which a material begins to undergo permanent deformation.

If commercialized, the newly developed alloy is expected to contribute to improving the safety and durability of hydrogen storage vessels, pipelines, and cryogenic structures.

Professor Kim said, “We have demonstrated that cryogenic nanotwin engineering can overcome the long-standing trade-off between the strength of metallic materials and their resistance to hydrogen embrittlement. We expect this approach to provide a new direction for the design of next-generation structural materials, including those used in hydrogen storage and transportation infrastructure.”

Reference: https://doi.org/10.1080/21663831.2025.2596162