ELECTROCHEMICAL STUDIES OF THE INFLUENCE OF BERYLLIUM ON THE CORROSION-RESISTANCE OF NI-25CR-1OMO CAST ALLOYS FOR DENTAL APPLICATIONS

Whereas addition of beryllium into Ni-based dental alloys can improve their casting properties, its effect on the corrosion behavior may be deleterious. The influence of beryllium addition on the corrosion resi stance of Ni-25Cr-10Mo cast dental alloys has been investigated by dif ferent electrochemical techniques in artificial saliva and by measurin g the rate of dissolution through atomic absorption spectroscopy analy sis of the medium. The corrosion attack has also been examined by scan ning electron microscopy. The coherent results obtained from the diffe rent techniques indicate that a low beryllium content [below 0.6 weigh t percent (w/o)] has no significant influence when the alloy is expose d to artificial saliva, whereas higher beryllium content results in ne gative effects on the corrosion resistance of the alloy. Hence, despit e high content of chromium and molybdenum, the nickel-based dental all oy is susceptible to localized corrosion attack such as pitting and cr evice corrosion when the alloy contains higher levels of beryllium. Th is is due to the high heterogeneity of the alloys, i.e., the formation of an intermetallic NiBe phase in the eutectic structure which is sus ceptible to corrosion attack.