Internal friction of gamma-TiAl alloys at high temperature

Intermetallic gamma-TiAl based alloys of engineering interest with respect to high temperature applications are two-phase alloys consisting of gamma-T iAl (ordered face-centered tetragonal structure) and az-Ti,Al (ordered hexa gonal structure). For this investigation a gamma-TiAl based alloy with a co mposition of Ti-46.4 at%Al-4 at% (Cr, Nb, Ta, B) was studied utilizing a lo w frequency subresonance apparatus at frequencies between 0.01 and 10 Hz. A bove 1000 K, the damping increases strongly up to Q(-1)=0.2. The frequency and temperature dependence of the high-temperature background was analysed by applying a Maxwell rheological model far viscoelastic relaxation includi ng a distribution of relaxation limes. The activation enthalpy of H=3.9 eV agrees well with that from creep experiments (H=3.6 eV) carried out at temp eratures between 973 and 1073 K at 200 MPa. The results are discussed in te rms of diffusion controlled dislocation climb. (C) 2000 Elsevier Science S. A. All rights reserved.