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How can tungsten be both brittle and tough?

Have you ever wondered, while observing the composite materials showcased in some of our recent posts (post #1, post #3, post #4), how an element like tungsten can exhibit both brittleness and flexibility at the same time? It seems contradictory, doesn’t it? Comparisons to reinforced concrete may be misleading, as the reinforcing material typically differs from the surrounding matrix. However, in tungsten fiber-reinforced composites, both the fiber and matrix are composed of tungsten. This raises the question: why are tungsten fibers ductile while the matrix remains brittle? Today’s image of the week provides a fresh perspective on our composite from the initial post. It reveals the distinct structures of the fiber and matrix, manipulated through potassium doping and wire drawing techniques. Potassium doping involves adding small amounts of potassium to the tungsten, which creates structural defects in its crystal lattice. These defects facilitate dislocation movement within the lattice, enhancing ductility during wire drawing. Several decades of experience in manufacturing incandescent light-bulb wires by our industrial partners, such as Osram GmbH, have paved the way for such innovative solutions and even allow the integration of tungsten fiber-reinforcements.

If you would like to learn more, here are some publications on this topic that provide nice background information:

Advanced materials for a damage resilient divertor concept for DEMO: Powder-metallurgical tungsten-fibre reinforced tungsten; Fusion Engineering and Design Volume 124, November 2017, Pages 964-968

Development of advanced high heat flux and plasma-facing materials; Ch. Linsmeier et al 2017 Nucl. Fusion 57 092007

Scanning electron microscope (SEM) image of mechanically tested yarn-based tungsten fiber-reinforced tungsten. Tungsten filaments were supplied by Osram GmbH, image taken by Alexander Lau, FZJ.
Alexander Lau, Doctoral researcher IEK, Materials and Components, Institut für Energie- und Klimaforschung, Forschungszentrum Juelich GmbH, picture courtesy of Alexander Lau.
Alexander Lau, Doctoral researcher IEK, Materials and Components, Institut für Energie- und Klimaforschung, Forschungszentrum Juelich GmbH. Picture courtesy of Alexander Lau.

“This image is clearly one of my favourites in our portfolio. It tells you so many details about the varying grain structure of tungsten fibers compared to bulk tungsten and also provides a perfect example of so-called pseudo-ductile mechanisms such as necking behaviour. Zooming into the fascinating structure with our analysis techniques simply makes a lot of fun. You learn more and more about the materials and how they behave under varying conditions.”

– Alexander Lau

Find Alexander Lau on LinkedIn and X: @LauAlexander164.


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