Microstructure and Oxidation Kinetics of Intermetallic TiAl after Si- and Mo- Ion-Implantation

Titanium aluminide alloys based on gamma-TiAl have a substantial potential for high temperature application. However, there are still problems concerning the high temperature oxidation behavior. Ion implantation is a promising tool to improve the oxidation resistance without disturbing the mechanical properties. A systematic investigation of the microstructure and phase development of silicon and molybdenum implanted gamma-TiAl is presented. For Si, the fluence is varied from 2.5·10¹⁶ cm^-2 to 8·10¹⁷ cm^-2 at an implantation energy of 1 MeV resulting in a local con-centration of Si between 1 at% and 35 at% at a projected range of 1 µm measured by AES depth profiling. Grazing incidence XRD and transmission electron microscopy show the formation of a buried Ti_5Si3 enriched layer at 650 °C, which acts as a diffusion barrier for oxygen. Long term TGA oxidation tests at 900 °C in air show a positive effect in the beginning of oxi-dation for the fluence of 8·10¹⁷ cm^-2. After a few hours the oxidation kinetic is similar to unimplanted Ti50Al, but the mass gain after 100 h is still 30 % smaller. The influence of the local Si concentration on the oxidation behavior is discussed. Implantation of Mo at 180 keV (2·10¹⁶ cm^-2 and 1·10¹⁷ cm^-2) has only minor influence on the oxidation at 900 °C. After implantation, Mo precipitates are found for the high fluence.