  Advanced g-TiAl based intermetallics Mo-bearing have been developed to obtain
the fine-grained microstructure required for superplastic deformation to be
used during further processing. In the present work we have studied an alloy of
Ti-46Al-1Mo-0.2Si (at%) with two different microstructures, as-cast material
with a coarse grain size above 300 mm, and the hot extruded material exhibiting
a grain size smaller than 20 mm. We have used a mechanical spectrometer
especially developed for high temperature internal friction measurements to
study the defect mobility processes taking place at high temperature. The
internal friction spectra at different frequencies has been studied and
analyzed up to 1360 K in order to characterize the relaxation processes
appearing in this temperature range. A relaxation peak, with a maximum in
between 900 K and 1080 K, depending on the oscillating frequency, has been
attributed to Ti-atoms diffusion by the stress-induced reorientation of
Al-VTi-Al elastic dipoles. The high temperature background in both
microstructural states, as-cast and extruded, has been analyzed, measuring the
apparent activation parameters, in particular the apparent energies of
Ecast(IF) 4.4 +- 0.05 eV and Eext(IF) 4.75 +- 0.05 eV respectively. These
results have been compared to those obtained on the same materials by creep
deformation. We may conclude that the activation parameters obtained by
internal friction analysis, are consistent with the ones measured by creep.
Furthermore, the analysis of the high temperature background allows establish
the difference on creep resistance for both microstructural states
