Oxidation of the Three-Phase Alloy Cu-20Ni-20Cr AT 973-1073 Κ in 101 kPa O2

The oxidation of a ternary Cu-Ni-Cr alloy containing approximately 20 wt% Ni and 20 wt% Cr (Cu-20Ni-20Cr) and composed of a mixture of three phases has been studied in 101 kPa (1 atm) O-2 at 973-1073 K. The alloy matrix was composed of the phase with the largest copper and lowest chromium content, while the other two phases, much richer in chromium, formed a dispersion of isolated particles. By high temperature oxidation this alloy formed complex external scales containing mixtures of the oxides of the various components and double oxides plus an irregular inner region composed of a mixture of alloy and oxides, which did not correspond to the classical structure of the zones of internal oxidation, while the alloy/scale interface was very irregular. This behavior differs from that of another two ternary Cu-Ni-Cr alloys with similar chromium content but richer in nickel and containing only one or two phases, which formed protective continuous chromia scales after rather short initial oxidation periods. The lack of formation of continuous chromia layers for Cu-20Ni-20Cr is attributed to the limitations of the diffusion of the alloy components in the metal substrate imposed by its multiphase nature.