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

Grain and grain boundary diffusion coefficients in alumina scales on F eCrAl-based ODS alloys have been determined. The boundary diffusion-co efficients have been derived by combining gravimetrically determined g rowth rate data with SEM and TEM analyses of the oxide scale microstru cture. The diffusion coefficients determined have been used as input p arameters for a computer model describing the oxygen isotope exchange between grain and grain boundary in the alumina scale which forms duri ng a two-stage oxidation using O-18-tracers. This comparison of the ca lculated tracer profiles with profiles determined experimentally by SI MS allows the estimation of the lattice diffusion coefficient of oxyge n in the alumina scale.