Improvement of the high temperature oxidation resistance of Ti50Al via ion-implantation

The TiAl intermetallic compound is very promising for high temperature applications, because of its good high temperature strength and its low density. At temperatures exceeding 800 degrees C, the low oxidation resistance is a limiting factor. It is known. that Cl doping reduces the oxidation strongly even in very low concentrations of about 500 ppm ('microalloy'). In the present investigation ion beam implantation is used to dope the material close to the surface quantitatively. The well-defined depth profile obtained after implantation provided a means to monitor the diffusion of additives during oxidation. Implantation of Cl- ions (1 MeV, 10(15)-10(17) cm(-2)) results in a systematic reduction of the oxidation at 900 degrees C in air for doses greater than or equal to 10(16) cm(-2). AES measurements were performed to investigate the diffusion process during oxidation. A microscopic model will be proposed for the enhanced oxidation resistance. For beneficial effects of Silicon a higher concentration is required ('macroalloy`). Therefore high-dose implantations were carried out (upto 8x10(17) cm(-2)). The change in phase composition, microstructure and the oxidation behaviour will be discussed. (C) 1999 Elsevier Science B.V. All rights reserved.