THE AIR OXIDATION OF 2-PHASE FE-CU ALLOYS AT 600-800-DEGREES-C

The air oxidation of three Fe-Cu alloys containing 25, 50, and 75 wt.% Cu has been studied at 600-800 degrees C. The oxidation followed the parabolic law only approximately with rates lower than those of the pu re constituent metals. The scales were always composed of an inner lay er containing a mixture of copper metal and iron oxide and of an outer oxide layer whose composition depended on the copper content of the a lloy. For the two alloys richer in iron the external layer was compose d mostly of iron oxides with some copper-rich particles which oxidized only in the external-scale zone. For the alloy richest in copper the external layer contained a complex mixture of iron oxides, copper part icles and double Fe-Cu oxides surmounted by an outermost copper-oxide layer. No significant iron depletion was observed in the alloys beneat h the region of internal oxidation. The peculiar scale microstructure observed for these alloys is considered mainly as a consequence of the ir two-phase microstructure and of the limited solubilities of the two components in one another.