Change in the surface composition of amorphous FeCrMoPC alloys during air exposure

X-ray photo-electron spectroscopy (XPS) has been used to investigate the oxidation behavior of amorphous Fe8CrxMo13P7C(x = 0, 2, 4, 6) alloys at room temperature. Thicknesses of surface films on these alloys increase continuously throughout air exposure for more than one week. XPS analysis reveals that air oxidation of specimens at ambient temperature results in an increase in concentration of oxidized iron species in surface films due to preferential oxidation of iron. Contrary to iron, concentrations of chromium and molybdenum species in the surface films decrease as oxidation proceeds. The addition of molybdenum to FeCrPC alloys hinders thickening of surface films and retards the decrease in concentrations of chromium and molybdenum in the films. Very little oxidized phosphorus species have been detected in the surface films at all oxidation times.