Microstructure and oxidation kinetics of intermetallic TiAl after Si- and Mo- ion implantation

Titanium aluminide alloys based on γ-TiAl have a substantial potential for high-temperature applications. However, there are still problems concerning the high-temperature oxidation behavior. Ion implantation is a promising tool for improving the oxidation resistance without disturbing the mechanical properties. A systematic investigation of the microstructure and phase development of silicon- and molybdenum-implanted γ-TiAl is presented. For Si, the fluence is varied from 2.5×1016 to 8×1017 cm−2 at an implantation energy of 1 MeV resulting in a local concentration of Si between 1 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 Ti5Si3 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 oxidation for the fluence of 8×1017 Si cm−2. After a few hours the oxidation kinetics 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 and 1×1017 cm−2) has only a minor influence on the oxidation at 900°C. After implantation, Mo precipitates are found for the high fluence.