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

The effect of ion beam implantation and plasma immersion ion implantation o f chlorine on the high temperature oxidation of titanium aluminides above 8 00 degrees C in air was investigated. Thermogravimetric oxidation tests (TG A) 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 o f the 'Cl-effect' will be discussed. A systematic variation of the implanta tion energy and fluence shows that there is a narrow regime of Cl concentra tion for optimum protective effect. The time to form a protective Al2O3 lay er depends on the local Cl concentration. The oxidation rate after this inc ubation time is reduced by about two orders of magnitude compared to untrea ted Ti50Al and is nearly independent of the fluence. The implantation energ y is not a sensitive parameter because the implanted chlorine profile chang es very quickly during high temperature oxidation. (C) 2000 Elsevier Scienc e S.A. All rights reserved.