Thermodynamische Untersuchungen zur Korrosion von binaeren und ternaeren Titanaluminiden

Titanium aluminide alloys based on Ti_3Al and TiAl are of particular interest for the development of light weight materials because of their low density. These alloys can be used for parts of the jet turbine as well as for the airframe. Alloys at high temperatures have to form a protective oxide scale on their surface. Instead of the formation of a protective alumina scale titanium aluminides show the rapid growth of mixed oxides of TiO_2 and Al_2O_3 on their surface which is detrimental. It is reported in the literature, that Ta, W, Cr, and especially Nb improve the oxidation resistance of titanium aluminides. Various mechanisms have been proposed to explain this improvement. One explanation bases on the increase of the thermodynamic activity of aluminium relative to that of titanium in the alloys which would then favour the formation of a stable alumina scale. Fundamental thermochemical data have to be available for the alloys considered, in order to check this explanation. Vaporization studies by Knudsen effusion mass spectrometry were carried out for the determination of these thermochemical data. The thermodynamic activities of Ti and Al were determined for the first time for the complete composition range of the Ti-Al system in the temperature range of 1200-1600 K. (orig.)Dissertation submitted by M. EckertSIGLEAvailable from TIB Hannover: RA 831(3399) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman