Hydrogen permeation through TiAlN-coated Eurofer '97 steel

Any future fusion reactor will require a structurally sound vacuum chamber that is able to withstand the attack of hydrogen produced in the transmutation reactions, while at the same time exhibiting the rapid decay of any induced radioactivity. However, the Eurofer '97 steel, which has already been chosen for the DEMO reactor, although possessing reduced activation, remains very susceptible to hydrogen. In this study we have looked at the effectiveness of thin, TiAlN coatings with respect to the permeability of hydrogen at 400 °C. Our results reveal that the coating forms a columnar structure, with evidence of epitaxy at the substrate-coating interface, and that this coating can produce a permeation reduction factor for hydrogen of up to 20,000. This is substantially higher than any other coating reported for this type of steel. Furthermore, the relatively low costs associated with such films and the breadth of knowledge that already exists about their characteristics suggest that such a combination of a TiAlN coating and the Eurofer '97 steel could be a very promising material for reactor technologies.