Development of High Temperature Coatings on gamma-TiAl

Kurzfassung

γ-TiAl based titanium aluminides are promising candidates for high temperature applica-tions in the field of aircraft and automotive industry due to their low density as well as good mechanical properties. However, γ-TiAl exibits a low oxidation resistance at tem-peratures above 750°C. Therefore, it is necessary to improve the oxidation resistance of that lightweight structural material especially for long-term use. In this study specific protective coatings deposited by magnetron-sputter technique were developed to improve the oxidation behaviour of γ-TiAl by suppressing the formation of titania. Three concepts will be discussed realizing the designated oxidation resistance: 1) increasing the thermodynamic activity of aluminium aiming at the formation of a slow growing continuous alumina scale, 2) decreasing the activity of titanium to reduce the growth of titania, directly, as well as the 3) combination of these both approaches. The oxidation behaviour of the developed coatings will be evaluated by microstructural investigations as well as by analysing the oxidation kinetics. Additionally, the application potential of thermal barrier coatings on γ-TiAl deposited by electron beam physical vapour deposition will be discussed. Coating systems with and without an oxidation protective intermediate layer were investigated focussing on the influence of the ceramic top layer on formation of the thermally grown oxide scale.