Influence of niobium ion implantation on the oxidation behaviour of TiAl under thermal cycle conditions

TiAl specimens measuring 15×10×2 mm were implanted with Nb ions of varying doses between 1.2×1021 and 1018 ions·m−2 at an acceleration voltage of 50 keV. Their oxidation resistance was assessed by cyclic oxidation tests with temperature varying between room temperature and 1200 K in a flow of purified oxygen under atmospheric pressure. The holding time at temperature was 72 ks (20 h) or 3.6 ks (1 h). Conventional metallographic examinations were performed for implanted specimens and oxidised specimens using glancing angle XRD, AES, SIMS, SEM and EDS. The doses of 1.2×1021 and 1020 ions·m−2 result in the formation of very protective scales very rich in Al2O3, although less protective scales are formed on the specimen edges for the latter dose owing to the geometric condition. The excellent oxidation resistance obtained is attributable to the formation of Al2O3 layers in the scale during the initial stages of oxidation. On the other hand, implantation with doses smaller than those is ineffective for improving oxidation resistance. The oxidation kinetics is nearly linear with occasional mass losses due to the repeated partial spallation of scales. The implantation of Ar ions of 1.2×1021 ions⋅m−2 significantly enhances the oxidation.