EFFECTS OF ACTIVE ELEMENTS Y AND Ce ON HIGH TEMPERATURE OXIDATION OF Fe-25Cr-40Ni ALLOY

摘要

The effects of small amount（≥0.05%）of active elements Y and Ce in Fe-25Cr-40Ni al-loy have been investigated on the kinetics of early stage of high temperature oxidationas well as composition and microsructure of oxide film by ion backscattering and slowpositron beam.The results show that Y and Ce can reduce evidently the high tem-perature oxidation rate of FeCrNi alloy at early stage and can effectively enhance theCr₂O₃ formation and retard the oxide formation of Fe and Ni in the surfacelayer thusthe microstructure of the oxide film is improved.Y and Ce enter the oxide film andconcentrate within several tens nanometres from surface of the outer layer.The mech-anism of oxidation resistance for Ce is different from Y.Ce can decrease the densityof vacancy defects in oxide layer,so the cations are restrained from diffusion outwardthrough vacancies.While Y can control the outward diffusion of cations through va-cancies at the early statge of oxidation（shorter than 12 min）,aften that restrained thecations from diffusion outward along grain boundaries up to 60 min oxidation.