Oxidation of Al-Co Alloys at High Temperatures

In this work, the high temperature oxidation behavior of Al(71)Co(29) and Al(76)Co(24) 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-Al(13)Co(4) and Z-Al(3)Co 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 Al(2)O(3) 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 Al(71)Co(29) and Al(76)Co(24) 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.