Ti2AlNb-Coated Refractory Alloys for Generation IV Nuclear Reactor Construction

No material of construction is currently approved for use at the high temperatures found in proposed Generation IV nuclear reactors. The Generation IV helium-cooled designs will operate at 800-1000°C, temperatures far above those of their Generation III forbearers. At these temperatures, normal steels lose most of their strength, and oxidation attacks even stainless ferritic steels. Even at the lower temperatures of the Generation IV sodium-cooled reactors, materials are needed that can resist liquid metals and withstand temperatures that might arise during an upset or accident. This project will investigate a well-known refractory alloy for this application, niobium-1%zirconium (Nb-1%Zr), a material that is know to have much higher creep strength than any steel, and that is known to show less short-term afterheat than most other material choices. Oxidation resistance will be added to this alloy by coating it with Ti2AlNb (atomic composition 50a%Ti, 21a%Al, 29a%Nb), which is known to be oxidation resistant. In addition, this material should adhere to Nb-1%Zr because it has the same atomic structure and the same average atomic density. A hypersonic, cold spray coating technique will be used to apply the T2i2AlNb in a way that should create an adherent coat with less oxygen or hydrogen impurities than other spray coatings. Phase I will demonstrate that the hypersonic cold-spray coating produces an adherent Ti2AlNb coat, that the coated material retains the good stress-strain behavior of the individual materials, and that the coat delivers oxidation and hydrogen-embrittlement resistance at 400 and 900°C. Commercial Applications and other Benefits as described by the awardee: In addition to the application to Generation IV nuclear power reactor use, the commercialization of other coated products should result from this project. Such coating would be attractive choices for tank armor, turbine blades, light-weight aircraft components, and prosthetic implants.