A15 superconductors: An alternative to niobium for RF cavities

Since the international committee for future accelerators recommended that the linear collider design should be based on the superconducting technology, the scientific world interest is now focused on further developments of new resonant cavities fabrication technics and cost reduction. Besides the attempt to improve the Nb sputtered on Cu accelerating structures performances, it is important to pursue research on new materials. The goal will be the achievement of superconducting cavities working better than the Nb ones at 4.2 K. Among the possible candidates, A15 compounds appear to be the most promising. Three of them were chosen: Mo–Re system which shows the A15 phase far from the stoichiometric composition (Mo3Re), V3Si that has a really high RRR value, Nb3Sn that is the only A15 compound already used for a resonant accelerating structure [G. Muller, P. Kneisel, D. Mansen, H. Piel, J. Pouryamout, R.W. Roeth, in: Proceedings of the 5th EPAC, London, 1985, p. 2085] and we obtained some interesting preliminary results. We are setting up a 6 GHz cavities measurement system: it is very simple, fast to use and it will give us the opportunity to make such small resonators become our samples

Protection from oxidation of second and third generation TiAl intermetallic alloys by magnetron sputtering deposition of a TiAl/TiAlN coating

A two-layer TiAl/TiAlN coating was deposited by High Power Impulse Magnetron Sputtering on the surface of three TiAl intermetallic alloys for improving their oxidation resistance. The effectiveness of the surface coatings was tested in a facility designed for simulating the service conditions of turbine engines components. The response of uncoated and coated samples was compared during thermal cycling up to 1000 °C under oxidizing environment. The growth of oxide layers and the degradation of the coatings were investigated by X-ray Diffraction, Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy and X-ray Photoelectron Spectroscopy. The surface coating was found to greatly improve the oxidation resistance of Ti-47Al-2Cr-8Nb and Ti-43.5Al-4Nb-1Mo alloys, while more limited benefits were observed for the Ti-48Al-2Nb-0.7Cr-0.3Si alloy. The different performance of the same coating deposited on different substrates has been tentatively attributed to the different alloying elements present in the intermetallic substrate, and that can diffuse towards the protective coating and the growing oxide layer