Oxidation behavior of TiAl protected by Al and Nb combined ion implantation at high temperature

Abstract

The combined ion implantation of Nb at 1173 K and Al at 973 K on a γ-TiAl based alloy Ti–48Al–1.3Fe–1.1V–0.3B (at.%) was conducted with a dose of 3.0×10 17 ions/cm 2 and at an accelerating voltage of 50 kV for each element with different sequences. The implanted layer was contaminated by C during the Nb implantation at 1173 K. The isothermal oxidation behavior of the above-treated alloys was investigated at 1173 K for 349.2 ks in air using a thermobalance. Auger electron spectroscopy (AES), X-ray diffractometry (XRD) and scanning electron microscopy (SEM) were employed to characterize the modified layer and oxide scale. The Al + Nb implanted alloy shows excellent long-term oxidation resistance due to the formation of a continuous and compact Al 2O 3 oxide scale. The co-existence of Nb and C in conjunction with the Al enrichment in the modified layer could inhibit the inward diffusion of O and prolong the beneficial effect of Nb and thus lead to the formation of the above protective scale. To the contrary, the oxidation rate of the Nb + Al implanted alloy remained very low in the first about 100 ks exposure and then accelerated. It is concluded that the C beneficial effect derived from the Nb and C layer formed during the 1173 K Nb implantation was weakened by the following Al implantation. The rapid consumption of Nb and fast inward diffusion of O finally contributed to the poor long-term oxidation resistance of the Nb + Al implanted alloy.