Abstract
ABSTRACTAn intermetallic Ti-46Al-9Nb (at%) alloy with different microstructures (near gamma, duplex, and fully lamellar) was studied by internal friction measurements at 300 K to 1280 K using different frequency ranges: (I) 0.01 Hz to 10 Hz and (II) around 2 kHz. The loss spectra in range I show (i) a loss peak of Debye type at T ≈ 1000 K which is only present in duplex and fully lamellar samples; (ii) a high-temperature damping background above ≈ 1100 K. The activation enthalpies determined from the frequency shift are H = 2.9 eV for the loss peak and H = 4.1–4.3 eV for the high-temperature damping background. The activation enthalpies for the visco-elastic high-temperature damping background agree well with values obtained from creep experiments and are in the range of those determined for self-diffusion of Al in TiAl. These results indicate that both properties (high-temperature damping background and creep) are controlled by volume diffusion-assisted climb of dislocations. The loss peak is assigned to diffusion-controlled local glide of dislocation segments which, as indicated by transmission electron microscopy observations, are pinned at lamella interfaces.
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