Tungsten crystal lattice distorted by deuterium plasma.

Tungsten's Breaking Point: New Insights into Hydrogen Embrittlement

Reese Marlowe in Tech & Innovation August 2025 • 5 min read.

"Nanoindentation tests reveal how deuterium plasma exposure affects the mechanical properties of tungsten, offering critical insights for fusion energy applications and material science. Embrittlement may be improved by material exposure time."

Tungsten (W) stands as a pivotal material in the construction of ITER's divertor, a component vital for handling extreme heat and particle fluxes within fusion reactors. Its selection is primarily due to its remarkable thermal conductivity, exceptionally high melting point, and minimal erosion rate. These properties make tungsten an ideal candidate for withstanding the intense conditions inside a fusion reactor, where temperatures can soar to millions of degrees Celsius.

Another critical advantage of tungsten is its low tritium retention. Tritium, a radioactive isotope of hydrogen, poses safety and operational challenges in fusion reactors. Tungsten's ability to limit the absorption and retention of tritium is essential for maintaining the safety and efficiency of fusion operations, reducing the risk of radioactive leaks and simplifying waste management.

However, experiments have revealed that under severe loading conditions, such as exposure to high fluxes of deuterium, helium, and neutron particles, tungsten can undergo significant surface modifications. These alterations can lead to a dramatic degradation of the material's thermal and mechanical properties, potentially compromising its structural integrity and performance within the reactor. Recent studies using linear plasma devices to expose tungsten to deuterium under transient heat loads have shown severe surface damage, underscoring the impact of hydrogen embrittlement on tungsten.

Unveiling the Effects of Deuterium Plasma on Tungsten

Tungsten crystal lattice distorted by deuterium plasma.

Hydrogen embrittlement is a well-recognized phenomenon that affects many metals, where the presence of hydrogen can reduce strength and ductility, increasing the likelihood of failure. While extensively studied in materials like steel, the effects of hydrogen embrittlement on tungsten in hydrogen-rich environments have not been as thoroughly investigated. Recent research has begun to focus on how deuterium plasma exposure affects the mechanical properties of tungsten, employing nanoindentation techniques to probe near-surface changes.

Nanoindentation is a highly sensitive method for assessing the mechanical properties of materials at the nanoscale. By pressing a small indenter tip into the surface of a material and measuring the force and depth of penetration, scientists can determine properties such as hardness and elastic modulus. This technique is particularly useful for studying surface modifications caused by plasma exposure, which typically occur within a few micrometers of the surface.

Several studies have produced contradictory results regarding the hardness of tungsten after deuterium plasma exposure. To clarify these discrepancies, researchers conducted nanoindentation tests on both exposed and unexposed tungsten samples at varying desorption times. Here's what they found:

A decrease in the pop-in load, indicating easier dislocation nucleation.
An increase in hardness in the exposed tungsten sample.
Grain orientation had no significant impact on the pop-in load.
After a desorption time of 168 hours, both pop-in load and hardness began to revert towards the reference state.

The reduction in pop-in load is explained by the defactant theory, which suggests that the presence of deuterium facilitates dislocation nucleation, making it easier for dislocations to form and move within the tungsten lattice. The increase in hardness is attributed to two possible mechanisms: the defactant theory and hydrogen pinning of dislocations. These mechanisms suggest that deuterium atoms may either promote the formation of more dislocations or impede their movement, both of which can lead to increased hardness.

Implications and Future Directions

This research provides critical insights into the effects of deuterium plasma on the mechanical properties of tungsten, a key material in fusion reactors. Understanding these effects is vital for predicting the long-term performance and durability of tungsten components in fusion environments. The observed recovery of mechanical properties after extended desorption times suggests that the impact of deuterium exposure under these conditions may not cause irreversible damage, providing a glimmer of hope for mitigating embrittlement. Future studies should focus on exploring these mechanisms in greater detail and developing strategies to enhance the resistance of tungsten to hydrogen embrittlement, ensuring the reliable operation of fusion reactors.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1557/jmr.2018.305, Alternate LINK

Title: Hydrogen Embrittlement Of Tungsten Induced By Deuterium Plasma: Insights From Nanoindentation Tests

Subject: Mechanical Engineering

Journal: Journal of Materials Research

Publisher: Springer Science and Business Media LLC

Authors: Xufei Fang, Arkadi Kreter, Marcin Rasinski, Christoph Kirchlechner, Steffen Brinckmann, Christian Linsmeier, Gerhard Dehm

Published: 2018-09-04

Everything You Need To Know

Why is tungsten chosen as a key material for the divertor in fusion reactors like ITER?

Tungsten is used in the ITER divertor due to its high thermal conductivity, high melting point, and low erosion rate, which allow it to withstand the extreme heat and particle fluxes inside a fusion reactor. Additionally, tungsten's low tritium retention is crucial for maintaining safety and reducing radioactive leaks, making it ideal for fusion applications.

How does hydrogen embrittlement specifically impact the structural integrity of tungsten in fusion environments?

Hydrogen embrittlement affects tungsten by reducing its strength and ductility, increasing the likelihood of material failure under stress. This occurs due to the presence of hydrogen isotopes like deuterium, which can alter the mechanical properties of tungsten, making it more susceptible to cracking and degradation, especially under the severe conditions found in fusion reactors.

What is nanoindentation, and how does it help in understanding the effects of plasma exposure on tungsten?

Nanoindentation is used to measure the mechanical properties of tungsten at the nanoscale. This technique involves pressing a small indenter tip into the material's surface and measuring the force and depth of penetration. It helps in determining properties like hardness and elastic modulus, providing insights into how deuterium plasma exposure alters tungsten's near-surface characteristics, which is crucial for assessing its durability in fusion environments.

In what specific ways does deuterium plasma exposure alter the mechanical properties of tungsten, according to recent research?

Deuterium plasma exposure affects the mechanical properties of tungsten by decreasing the pop-in load, which indicates easier dislocation nucleation, and increasing hardness. The defactant theory explains the reduction in pop-in load by suggesting deuterium facilitates dislocation nucleation, while increased hardness results from deuterium either promoting dislocation formation or impeding their movement. The effects of this exposure on tungsten are significant for fusion reactor materials.

What implications does the observed recovery of tungsten's mechanical properties have for mitigating embrittlement in fusion reactors?

The recovery of tungsten's mechanical properties after extended desorption times suggests that the impact of deuterium exposure under specific conditions may not cause irreversible damage. This offers potential strategies for mitigating embrittlement in fusion reactors. Future research should focus on understanding these mechanisms in greater detail to enhance tungsten's resistance to hydrogen embrittlement, ensuring reliable operation of fusion reactors. Strategies that can be implemented could include protective coatings.