Mechanical loss (internal friction) and creep experiments were carried out on specimens of a Ti-46.5at.%Al-4at.%(Cr,Nb,Ta,B) alloy with differently spaced fully lamellar microstructures. The creep tests were performed in a temperature range of 970 K to 1070 K at 175 MPa. For the mechanical loss measurements a low frequency subresonance torsion apparatus was applied, operating in the frequency range of 0.01 Hz to 10 Hz. The mechanical spectra show two phenomena: (i) A loss peak of Debye-type at 900 K (0.01 Hz) which is controlled by an activation enthalpy of 3.0 eV. The loss peak is related to thermally activated (reversible) motion of dislocation segments which are pinned at the lamellae interface and within gamma lamellae. (ii) A viscoelastic high temperature background above 1000 K with an activation enthalpy of 3.8 eV. This value agrees well with the activation enthalpy of 3.6 eV from creep experiments. Both high temperature background as well as creep are assigned to diffusion controlled climb of dislocations.
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We thank Prof. Dr. E. Arzt for helpful discussions and Plansee Aktiengesellschaft (Reutte, Austria) for providing sample material.
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Weller, M., Chatterjee, A., Haneczok, G. et al. Mechanical Properties of γ-TiAl Based Alloys at Elevated Temperatures. MRS Online Proceedings Library 646, 92–97 (2000). https://doi.org/10.1557/PROC-646-N7.7.1