Oxidation of powder metallurgical Ag-Cr alloys in 1 atm O-2 at 700-800 degrees C

The oxidation of three Ag-Cr alloys with a nominal content of 17, 35 and 69 wt% Cr prepared by powder metallurgy has been studied in 1 atm of pure O-2 at 700 and 800 degrees C. As a consequence of their two-phase nature, thes e alloys form composite scales containing complex mixtures of chromia, a do uble Ag-Cr oxide and silver metal. The alloys more dilute in chromium under go a complex internal oxidation of chromium associated with the formation o f a layer of silver metal on top of the scale. The large chromium particles in the region of internal oxidation are not completely oxidized due to the slow rate of chromia growth. A continuous layer of chromia forms only on t he alloy containing 69 wt% Cr, but it is surmounted by an external layer of the double oxide. The internal oxidation of chromium is suppressed in this alloy, which corrodes significantly more slowly than those more dilute in chromium.