The perfect material for a fusion reactor is still to be found. EUROfusion’s Finnish Research Unit recently published a major breakthrough in material science – and it came by accident. High-entropy alloys, a combination of different metals, appear to be much more resistant towards radiation than pure ones.

“We heard about a project being carried out by Oak Ridge National Laboratory. They were testing hybrid metals under radiation influence” explains Kai Nordlund, materials physicist from the University of Helsinki. High-entropy alloys are a mixture of metal elements under roughly equal concentration.

Out of curiosity

The concept behind the creation of these alloys is ten years old and was first proposed by metallurgists. Some three years ago, Yanwen Zhang at Oak Ridge National Laboratory in Tennessee, co-Author of the study, initially used irradiation to process these new metal alloys, and shared the information with her colleagues Kai and Flyura Djurabekova in Finland. “Amazingly enough, prior to this no one had ever tried to mix several different elements using roughly equal compositions. So, we decided, out of curiosity, to test the samples for our purposes”, says the expert.

Beams of gold

Which combination would be the most resistant? The scientists ran experiments and simulations while using different mixtures with nickel. They then tested the new metals under reactor conditions. Apparently, high-entropy alloys, a complete new class of material, could become the new super material for nuclear power plants. But there is still a long way to go.

A high-entropy alloy captured using a scanning electron microscope. Picture: Sheng Guo

A high-entropy alloy captured using a scanning electron microscope. Picture: Sheng Guo

The high-alloy needle in the haystack

To date, the labs at Oak Ridge and the University of Helsinki have just combined two, three or four elements. “There are already millions of possible mixtures assuming you only use 20 regular metals in five different combinations”, says Kai. It is important now that many groups study the properties of the different material mixes by employing simulations. These experiments should be sufficient to find the high alloy needle in the haystack, the material mix which will be capable of surviving the radiation. “If good results keep coming up, then this ought to be incorporated into the EUROfusion programme”, adds the material physicist.

Used in DEMO diagnostics?

In order to become a feasible material in a nuclear plant, the new metal still has to undergo a very strict licensing procedure. Hence, it will take some time until high-entropy alloys will be permitted to enter a fusion plant. “My guess is that they will be used in small parts of the reactor first, maybe initially in some diagnostics of DEMO”, pictures Kai.