High Spatial Resolution AEM Observations of Yttrium Segregation in Chromia Scales Growth on Co-45%Cr

摘要

The addition of so-called ''reactive'' elements such as yttrium to alloys enhances the protective nature of Cr sub 2 O sub 3 or Al sub 2 O sub 3 scales. An A.E.M. study has been performed of scales grown at 1000 deg C for 25 h in pure O sub 2 on Co-45%Cr implanted at 70 keV with 2 x 10 sup 16 atoms/cm sup 2 of yttrium. In the unoxidized alloys it was calculated that the maximum concentration of Y was 13.9 wt % at a depth of about 17 nm. SIMS results showed that in the scale the yttrium remained near the outer surface. The grain size of the chromia scale was 200 to 300 nm. No yttrium was found inside featureless grains. Yttrium was found on all the grain boundaries and in some particles within the scale. (ERA citation 12:011613)