Internal friction measurements of gamma-TiAl

Single-phase gamma-TiAl polycrystals were prepared by extrusion. The compou nd possesses an Al content of 54.1 at. % and interstitial impurities typica l for technical-purity materials. Owing to dislocation pinning by theses im purities and precipitates, internal friction measurements show no relaxatio n between room temperature and 950 K. At 1100 K a relaxation maximum is obs erved with an activation enthalpy of H-eff-=(2.97 +/- 0.1) eV and a pre-exp onential factor of tau(0) = 2.5 x 10(-16+/-1) s, which can be attributed to the reorientation of structural defects. Above 1200 K the damping shows a frequency-dependent strong increase with temperature, which is characterist ic for diffusion-controlled climb of dislocations. (C) 1999 Elsevier Scienc e Ltd. All rights reserved.