Effect of Ni Addition on High Temperature Oxidation of Cu- 50Co Alloy

The oxidation of a ternary two-phase Cu-Ni-Co alloy containing approximately 20 mass% Ni and 50 mass% Co, balance Cu (Cu-20Ni-50Co), was studied at 973-1073K in lOlkPa 0 2 .The kinetic curves for the present alloy are irregular and deviate from the parabolic rate law and are composed of three quasiparabolic stages.At variance with the binary two-phase Cu-50Co alloy examined previously, which was unable to form the exclusive external scales of reactive component Co oxides over the alloy surface even after an extended period of oxidation, the present alloy formed an outmost layer composed of a CuO followed by a first dark layer of Co 3 0 4 and then by a slightly lighter innermost layer of CoO.Obviously, the addition of 20 mass% Ni to Cu-50Co alloy enables us to decrease the critical Co content required to form the most stable oxide and complete transformation from a mix internal oxidation composed of the Cu-rich metal phase with Co oxides to the formation of the exclusive external scales of Co oxides under a lower Co content.