Raman investigation of crevice corrosion in nickel-chromium dental alloys containing beryllium

The presence of the small amounts of Be which are often added to the Inconel-type Ni-Cr-Mo dental alloys to improve their castability leads to a dramatic increase of the corrosion processes in the presence of chlorides, with the formation of deep pits full of corrosion products. In this kind of alloys, crevice formation is normally unexpected and it is important to check whether Be is also able to promote crevice development. We showed that the metallurgical heterogeneities of these alloys, which are industrially used as-cast, are responsible for the tremendous increase of localized corrosion. We have proposed a simple configuration to simulate a crevice and to identify by Raman spectroscopy (RS) the corrosion products which are liable to appear, in order to characterize their differences with the products found in pits. This analysis is completed by results obtained using X-rays energy dispersive analysis (XEDS). A growth of spinels to the prejudice of the salts (molybdates, chromates) which are usually found in the pits is observed. (C) 1997 Elsevier Science Ltd.