A Ti-46.5 Al-4 (Cr, Nb, Ta, B) alloy (at.%) with different microstructures
(fine-grained primary annealed or coarse-grained fully lamellar) was examin
ed both by mechanical-loss (internal-friction) and creep experiments. The m
echanical-loss spectra (0.01-10 Hz), ranging from 300 up to 1300 K, show tw
o phenomena: (i) A loss peak at about 900 K (0.01 Hz) which occurs only in
samples with a lamellar microstructure. The activation enthalpy, determined
from the frequency shift, is 3.0 eV. The Debye-type peak is related to the
rmally activated reversible local movement of dislocation segments which ar
e pinned at the lamellae interfaces and within gamma lamellae. (ii) A high-
temperature damping background above 1000 K which is controlled by an activ
ation enthalpy of 3.8 to 3.9 eV. This value agrees well with the activation
enthalpy determined by creep tests and is in the range of values reported
for self-diffusion of Al. These results indicate that both properties (high
-temperature, background and creep) are controlled by volume diffusion-assi
sted climb of dislocations.