Microstructure evolution and oxidation resistance properties of oxide dispersion strengthened FeCrAl alloys at 1100 °C

Oxide dispersion strengthened (ODS) FeCrAl alloys were prepared by mechanical alloying (MA) and spark plasma sintering (SPS) technology. To reveal the high temperature oxidation properties, ODS FeCrAl alloys were exposed to dry air for various times (1h, 4h, 10h, 20h, 45h, 70h, and 100h) at 1100 °C to investigate the microstructure evolution. The results illustrated that a flat and adherent alumina scale was gradually thickened on the alloy substrate with the increase of the oxidation time. In particular, it was observed that large-size reactive element (RE) oxides were inclined to be associated with cavities close to the gas interface and these cavities were progressive evolution to be larger-size pores with longer exposure time, while tiny RE oxides were not dispersed with cavities after 100h oxidation. In addition, α-Al2O3 with a double-scale structure were mainly composed of inner columnar grains and outer equiaxed grains, as well, the growth of α-Al2O3 scales illustrated that the oxidation rate decreased with oxidation reaction proceeding. For one thing, Ti segregation along grain boundaries (GBs) near the gas interface decreased the outward diffusion of the Al ions to weaken the oxidation rate. Furthermore, the gradual coarsening of columnar grains near the alloy substrate implied a longer diffusion path of O atoms, thereby accounting for slower oxidation process. To sum up, ODS FeCrAl alloys with thinner oxide thickness demonstrated the superior oxidation resistance than other materials, which would make it one of the promising candidate structural materials applicated in accident-tolerant fuel (ATF) cladding materials.