Study of the reactive element effect in ODS iron-base alumina formers

Iron aluminide (Fe₃Al) and FeCrAl compositions were dispersed with 15 different oxides in order to study the effect of oxygen-active dopants on the high-temperature growth and adhesion of α-Al₂O₃ scales. In these model-type, oxide dispersion strengthened (ODS) systems, the chemical effects of various cation dopants were compared to the base-line effect of an Al₂O₃ dispersion. By conducting isothermal and cyclic oxidation tests and by characterizing the oxidation product, effects on scale adhesion, growth rate and microstructure were evaluated. The dopants were categorized based on their effectiveness in modifying the alumina scale. An Al₂O₃ dispersion yielded some improvement in oxidation behavior apparently by strengthening the relatively weak substrate. However, the type of improvements in adhesion and the change in growth mechanism associated with the addition of reactive elements such as Y were not achieved. In general, due to the weaker substrate and the inherently faster interfacial void formation, the dispersions were less effective in ODS Fe₃Al than in ODS FeCrAl.