Oxidation of Al-Co Alloys at High Temperatures

In this work, the high temperature oxidation behavior of Al₇₁Co₂₉ and Al₇₆Co₂₄ alloys (concentration in at.%) is presented. The alloys were prepared by controlled arc-melting of Co and Al granules in high purity argon. The as-solidified alloys were found to consist of several different phases, including structurally complex m-Al₁₃Co₄ and Z-Al₃Co phases. The high temperature oxidation behavior of the alloys was studied by simultaneous thermal analysis in flowing synthetic air at 773-1173 K. A protective Al₂O₃ scale was formed on the sample surface. A parabolic rate law was observed. The rate constants of the alloys have been found between 1.63 × 10^-14 and 8.83 × 10^-12 g cm^-4 s^-1. The experimental activation energies of oxidation are 90 and 123 kJ mol^-1 for the Al₇₁Co₂₉ and Al₇₆Co₂₄ alloys, respectively. The oxidation mechanism of the Al-Co alloys is discussed and implications towards practical applications of these alloys at high temperatures are provided.