THE AIR OXIDATION OF 2-PHASE CU-AG ALLOYS AT 650-750-DEGREES-C

The corrosion of three two-phase Cu-Ag alloys containing 25, 50, and 7 5 wt% Ag has been studied at 650 and 750 degrees C. In all cases the a lloys formed external scales of copper oxides. At the same time, an in ternal precipitation of Cu2O within a silver matrix was also produced, with an oxide volume fraction larger for the alloys richer in Cu. Ben eath this mixed layer a region of single-phase solid solution of Cu in silver formed for Cu-50Ag and especially for Cu-75Ag. Silver metal re mained in the metal-consumption zone, acting essentially as an inert m arker, except for a few particles with were incorporated into the grow ing scales. Both pure Cu and the alloys corroded parabolically, but th e rate constants for the alloys decreased with increased Ag content un der constant temperature. The various aspects of the corrosion of thes e alloys are examined by taking into account the possible effects asso ciated with the presence of two metal phases.