Yttrium diffusion in a chromia scale grown on a Ni-30 wt% Cr alloy

Abstract

Abstract Diffusion coefficients of yttrium in chromia (Cr2O3) scales grown on a Ni-30 wt% Cr alloy by high-temperature oxidation have been determined in the temperature range 800–1000°C in air. A thin yttrium-containing film on the oxide surface was produced by the deposition of a liquid solution of YCl3, and, after a diffusion treatment, the penetration profiles were established by secondary-ion mass spectrometry. The apparent diffusion coefficients were calculated from the thin-film solution of Fick's equation and, at the same time, the bulk and grain-boundary diffusion coefficients were obtained according to a model recently proposed in Orsay, in which the oxide surface roughness and the relationship between bulk, grain-boundary and apparent diffusion coefficients was considered. The results showed that yttrium diffusion in Cr2O3 scales obeys the relationships for bulk diffusion and for grain-boundary diffusion. The difference between the values for bulk and grain-boundary diffusion coefficients is abo...