Making brittle material pseudo-ductile: tungsten-fibre-reinforced tungsten

IPP has developed a new resistant composite material: tungsten-fibre-reinforced tungsten. It consists of pure tungsten with coated tungsten wires embedded.

Its combination of unique properties makes tungsten a promising candidate for use on directly plasma-facing components in a future fusion power plant. However, its inherent brittleness and corresponding lack of damage tolerance considerably limit its use.

A possible approach to a solution is to incorporate in the material structures with local stress redistribution, thus producing a kind of toughness, viz. increased resistance to failure. This externally introduced, enhanced toughness or “pseudo-ductility” can be achieved by, for instance, incorporating embedded fibres which can bridge or deflect cracks, or plastically deform. Ceramic-fibre-reinforced ceramics are an example of successful implementation of this concept.

Cross-section of tungsten-fibre-reinforced tungsten composite: The material was  produced by a newly developed technique, chemical vapour infiltration of tungsten. The circular structures with diametres of about 150 µm are cross-sections of the tungsten fibres.

In the frame of the project “Plasma-Wall Interaction” this idea was applied to tungsten. The metal is reinforced with coated long fibres from drawn tungsten wires. Samples of the new material have already been produced on a laboratory scale. Tomographic investigations with high-energy synchrotron radiation demonstrated that the mechanisms of toughness increase work in principle, and that the stability to embrittlement increases indeed. Bending tests on larger samples showed stable crack propagation, doubling of the load-bearing capability, and therefore doubling of the toughness. The results of these investigations showed that the idea of tungsten-fibre reinforcement of tungsten is basically applicable (“proof of principle”).

As next step after this “proof of principle”, it is currently being investigated whether tungsten-fibre-reinforced tungsten can be applied in a fusion reactor (“proof of concept”) and thus contribute to solving the power exhaust problem. The important aspects here are optimisation of the production process allowing larger and reproducible samples to be produced. Then an extensive material qualification can be carried out. This work is being conducted in close cooperation with the plasma physics division of the Institute of Energy and Climate Research at Forschungszentrum Jülich. These activities are complemented by intensive investigations of the basic materials science of this new material. An important concern of the work is the promotion of young scientists.

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