Protection of γ-based TiAl against high temperature oxidation using ion implantation of chlorine

The effect of ion beam implantation and plasma immersion ion implantation of chlorine on the high temperature oxidation of titanium aluminides above 800 degrees C in air was investigated. Thermogravimetric oxidation tests (TGA) were performed to examine the long term protection. Depth profiling with Auger electron spectroscopy (AES) was used to investigate Cl diffusion and oxide formation during the first stage of oxidation. A microscopic model of the 'Cl-effect' will be discussed. A systematic variation of the implantation energy and fluence shows that there is a narrow regime of Cl concentration for optimum protective effect. The time to form a protective Al2O3 layer depends on the local Cl concentration. The oxidation rate after this incubation time is reduced by about two orders of magnitude compared to untreated Ti50Al and is nearly independent of the fluence. The implantation energy is not a sensitive parameter because the implanted chlorine profile changes very quickly during high temperature oxidation. (C) 2000 Elsevier Science S.A. All rights reserved.