Thermodynamische Untersuchungen zur Korrosion von binären und ternären Titanaluminiden
Thermodynamische Untersuchungen zur Korrosion von binären und ternären Titanaluminiden
Titanium aluminide alloys based on Ti$_{3}$Al and TiAl are of particular interest for the development of light weight materials because oftheir low density. These alloys can be used for parts ofthe jet turbine as well as for the airframe. Alloys at high temperatures have to form a protective oxide s...
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Personal Name(s): | Eckert, M. (Corresponding author) |
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Hilpert, K. / Nickel, Hubertus | |
Contributing Institute: |
Publikationen vor 2000; PRE-2000; Retrocat |
Imprint: |
Jülich
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
1997
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Physical Description: |
200 p. |
Document Type: |
Report Book |
Research Program: |
ohne Topic |
Series Title: |
Berichte des Forschungszentrums Jülich
3399 |
Link: |
OpenAccess OpenAccess |
Publikationsportal JuSER |
Titanium aluminide alloys based on Ti$_{3}$Al and TiAl are of particular interest for the development of light weight materials because oftheir low density. These alloys can be used for parts ofthe 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$_{2}$O$_{3}$ 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 beenproposed 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 ofthe Ti-Al system in the temperature range of 1200-1600 K. To determine the influence of a third component on the activities of Ti and Al, these activities were measured in the alloys of the Ti-Al-X (X = Nb, Ta, W, Cr, Au) systems in thetemperature range of 1200-1600 K for the first time. The emphasis was laid on the Ti-Al-Nb system. In addition, phase diagram studies were carried out at temperatures of 1273, 1373, and 1473 K in order to determine the constitution of the alloys investigated by Knudsen effusion mass spectrometry. Also, partial enthalpies and entropies of mixing were determined for the alloys belonging to the $\gamma$-TiAl phase of the Ti-Al and Ti-Al-Nb systems. The solubility behaviour of Nb in the $\gamma$-TiAl phase was modelled by the application of a sublattice model based on the Bragg-Williams approximation. Mixing properties and the siteoccupancies resulted for different compositions and temperatures. |