Anodic behaviour of Al-refractory metal amorphous alloys

In order to understand the anodic behaviour of Al-Mo and Al-W amorphous all oys in the berate buffer electrolyte, samples of these alloys were polarize d galvanostatically. The resultant anodic films were thicker than the passi ve films formed during potentiodynamic polarization enabling detailed exami nation of the films and alloy substrates by surface analytical methods. AES investigations suggest that the anodic films formed at low and moderate vo ltages on Al-Mo or Al-W amorphous alloys consist of ill-oxide, whereas refr actory metals remain unoxidized and enriched at the film/substrate interfac e. Molybdenum and tungsten act as 'dissolution moderators', restraining the substrate dissolution process at the film/substrate interface. However, af ter anodization at high voltages (50 V), AES revealed the presence of an ox idized refractory metal in the inner part of the anodic film. Based on thes e results of growth of thick anodic films, the role of Mo and W in enhancin g the pitting corrosion resistance is discussed. (C) 1999 Elsevier Science S.A. All rights reserved.