Significance of crystallographic grain orientation for oxide scale formation on FeCrAl ODS alloys studied by AFM and MCs+-SIMS

Abstract

Single crystalline specimens were prepared by spark erosion of large grains in an extremely coarse textured bar of an FeCrAl based ODS alloy. These flat single crystalline specimens were studied in respect to oxidation behaviour at 800°C and 1,000°C in air. Initially the oxide scales appeared to grow by outward diffusion of aluminium but subsequently scale growth proceeded by grain boundary oxygen diffusion. The composition, grain size and growth rate of the transient oxide appeared to be dependent on the crystallographic orientation of the alloy. After the inward diffusion of oxygen had become dominant, the oxides on specimens with different crystallographic orientations showed clear differences in their growth rates. Correlation of SIMS results with quantitative grain size analysis performed by AFM showed that the different oxide growth rates, which pertained during longer exposure times, were related to differences in the oxide grain size and therefore the density of oxygen diffusion paths with different crystallographic orientations.