Air-oxidation behavior of a [(Co ₅₀Cr ₁₅Mo ₁₄C ₁₅B ₆)97.5Er2.5]93Fe7 bulk-metallic glass at 873 K to 973 K (60°C to 70°C)

The oxidation behavior of a [(Co50Cr15Mo14C15B6)97.5Er2.5]93Fe7 bulk-metallic glass (Co7- BMG) was studied over the temperature range of 873 K to 973 K (60°C to 70°C) in dry air. The oxidation kinetics of the Co7-BMG generally followed the parabolic-rate law, as its oxidation rates increased with temperature. The scaling rate of the Co7-BMG was significantly lower than that of pure Co, which indicates a better oxidation resistance for the amorphous alloy. The scales formed on the Co7-BMG consisted mostly of CoMoO4 and Co3O4, as well as minor amounts of CoO, Cr2O3, and uncorroded Co3B. The formation of CoMoO4 and Cr2O3 is responsible for the lower oxidation rates of the glassy alloy with respect to those of pure Co. In addition, the presence of Co3B further indicated that the crystallization of the amorphous substrate during the oxidation was taken place.