Air Oxidation of an Fe48Cr15C15Mo14B6Er2 Bulk Metallic Glass at 600–725°C

The oxidation behavior of an Fe48Cr15C15Mo14B6Er2 bulk metallic glass (Fe-BMG) was studied over the temperature range of 600-725 degrees C in dry air. The oxidation kinetics of the glassy alloy followed a two-stage parabolic rate law at T <= 650 degrees C, while the single-stage linear rate was observed at higher temperatures (T >= 675 degrees C). The oxidation rates of the Fe-BMG at T <= 625 degrees 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 degrees C, while typical hump iron oxides intermixed with minor amounts, of Cr2O3 and MoO2 were observed at T >= 675 degrees 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 degrees C.