Characterization of less common nitrides as potential permeation barriers

In a fusion reactor, the transport of hydrogen isotopes (primarily tritium) has to be controlled, from the point of view of fuel balance and retention in the reactor components, which can result in material degradation and spreading of radioactivity. To suppress this, tritium permeation barriers are developed. Suitable materials for the permeation barriers are those with low hydrogen isotope permeability - primarily ceramic materials, such as oxides, carbides and nitrides. In this study, coatings of six less common nitrides prepared by physical vapor deposition - namely AICrN, CrN, Cr2N, CrWN, WN and ZrN - were investigated. Besides basic characterization (elemental and phase composition, surface morphology and coating thickness), hydrogen permeation, adhesion, residual stress and thermal expansion were evaluated. All coatings were dense, crack-free and well adherent. The permeation reduction factor which was determined at 400 degrees C and 1 bar ranged from (similar to)10(2) to(similar to)5x 10(3) , the best performance being achieved by the ZrN coating. As these materials seem not to be investigated as hydrogen permeation barriers, they have a very high potential to be further improved.