DETERMINATION OF LATTICE AND GRAIN-BOUNDARY DIFFUSION-COEFFICIENTS IN PROTECTIVE ALUMINA SCALES ON HIGH-TEMPERATURE ALLOYS USING SEM, TEM AND SIMS

Grain and grain boundary diffusion coefficients in alumina scales on FeCrAl-based ODS alloys have been determined. The boundary diffusion-coefficients have been derived by combining gravimetrically determined growth rate data with SEM and TEM analyses of the oxide scale microstructure. The diffusion coefficients determined have been used as input parameters for a computer model describing the oxygen isotope exchange between grain and grain boundary in the alumina scale which forms during a two-stage oxidation using O-18-tracers. This comparison of the calculated tracer profiles with profiles determined experimentally by SIMS allows the estimation of the lattice diffusion coefficient of oxygen in the alumina scale.