Air-oxidation of a Co-based amorphous ribbon at 400–600 °C

The oxidation behavior of a commercial Co69B12Si12Fe4Mo2Ni1 amorphous ribbon (Co6-AR) was studied over the temperature range of 400–600 °C in dry air. The results showed that virtually no oxidation occurred at 400 °C. On the other hand, the oxidation kinetics of the Co6-AR alloy at 450–600 °C generally followed a multi-stage parabolic-rate law, and the parabolic-rate constants (kp values) tend to increase with increasing temperature. It was found that the oxidation rates of the glassy alloy are slower than those of pure Co, indicative of a better oxidation resistance. An exclusive scale of CoO was observed after the oxidation of the glassy alloy in the temperature range of interest, and several crystalline phases formed on the substrate beneath the scale, consisting of pure Co (both FCC and HCP structures), Co3B, Co2Si, CoFe, and Co2B (absent at 450 °C), which indicated the occurrence of crystallization.