Air oxidation of an Fe₄₈Cr₁₅C₁₅MO ₁₄B₆Er₂ bulk metallic glass at 600-725°C

The oxidation behavior of an Fe₄₈Cr₁₅C ₁₅Mo₁₄B₆Er₂ bulk metallic glass (Fe-BMG) was studied over the temperature range of 600-725°C in dry air. The oxidation kinetics of the glassy alloy followed a two-stage parabolic rate law at T ≤ 650°C, while the single-stage linear rate was observed at higher temperatures (T ≥ 675°C). The oxidation rates of the Fe-BMG at T ≤ 625°C were much lower than those of the commercial 304 stainless steel (304 SS), revealing the excellent oxidation resistance of the amorphous alloy. A continuous, thin layer of chromium oxide (Cr₂O₃) containing some iron was formed at T ≤ 650°C, while typical hump iron oxides intermixed with minor amounts of Cr₂O₃ and MoO ₂ were observed at T ≥ 675°C. In addition, a substrate phase transformation from the amorphous structure to Fe-Cr and FeCrMo crystalline phases was detected after the oxidation. Very likely, the formation of the non-protective Fe₃O₄ and MoO₂ breaks the scale integrity and allows the rapid cation/anion transportation, resulting in the fast linear-kinetics behavior of the Fe-BMG at T ≥ 675°C. © 2007 The Japan Institute of Metals.