The effect of aluminum ion implantation on the oxidation of an Fe-6 at.% Al alloy at 1173 K

Abstract

Samples of an Fe-6 at.% Al alloy were implanted with doses of 5×10¹⁶−3×10¹⁷ Al⁺ ions/cm² at 100 kV, and subsequently oxidized at 1173 K in O₂ gas at 27 kPa. By comparison with the behavior of unimplanted specimens, no effect on oxidation was observed if the dose of implant was less than 1×10¹⁷ Al⁺ ions/cm². At doses of 1×10¹⁷ Al⁺ ions/cm² or higher, a change in the oxide scaling morphology was effected from a duplex α-Fe₂O₃-α-Al₂O₃ scale to an α-Al₂O₃-enriched film with a dispersion of α-Fe₂O₃ nodules. Oxygen uptake by the high-dose samples was due principally to nodule formation and weight gains after 45 hr were lower by 50–70% as compared with the unimplanted material. Nucleation and growth of the nodules occurred only within the first 5 hr of reaction, but their presence acted as an upper limit on the benefits provided by implantation of aluminum. Nodule formation was shown to be characteristic of the oxidation properties of the alloy material, not an extraneous feature introduced by the implantation process itself. Surface preparation prior to implantation had little effect on oxidation: high-dose electropolished samples behaved similarly to mechanically polished samples when implanted to comparable doses.