Influence of implantation of Al, Si, Cr or Mo ions on the oxidation behaviour of TiAl under thermal cycle conditions

TiAl specimens measuring 15×10×2 in mm were implanted with Al, Si, Cr or Mo ions of a dose of 1021 or 1.2×1021 (for Cr only) 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 X-ray diffractometry (XRD), Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The implantation of Al or Si is effective to decrease the oxidation rate during the first near parabolic period of 130 ks, after which the implantation of Al results in breakaway oxidation, while the implantation of Si gives low oxidation rate for at least up to 800 ks. The implantation of Cr accelerates the oxidation during the initial period and then the partial scale spallation takes place leading to occasional mass losses. The implantation of Mo results in very slow oxidation rate for up to 1500 ks when the experiment was terminated. The same effect was obtained for the implantation of Mo under conditions of 40 keV and 2×1021 ions m−2. The excellent oxidation resistance obtained by the implantation of Si or Mo is attributable to the formation of virtually Al2O3 scales during the initial oxidation periods.