Grain Boundary Segregation of Yttrium in Chromia Scales

Implantation of a Co‐45 weight percent Cr alloy with a high dose of yttrium causes the oxidation rate of the alloy to decrease by about 100 times at 1000°C in pure oxygen. Also, the mechanism of growth of the scale changes from predominant cation diffusion to predominant anion diffusion, both of which occur along grain boundaries in the oxide. Segregation of yttrium ions to grain boundaries in the scales has been measured using EDX analysis in a STEM, and the reduction in oxidation rate and the change in growth mechanism have been attributed to segregation of yttrium at the grain boundaries. Less than 2 volume percent of particles have been found in a scale after 25h of oxidation at 1000°C, and it has been concluded that these particles do not have a significant effect on the oxidation mechanisms.