Axial-torsional thermomechanical fatigue of a near-γ TiAl-alloy

The uniaxial, torsional and axial-torsional thermomechanical fatigue (TMF) behavior of the near-gamma TiAl-alloy TNB-V5 was investigated. TMF tests were performed at 400-800 degrees C with mechanical strain amplitudes ranging from 0.15% to 0.7%. The tests were conducted thermomechanically in-phase (IP) and out-of-phase (OP). For the same lifetimes, uniaxial IP tests required the highest strain amplitudes, while OP test conditions were most damaging and needed the lowest strain amplitudes. The Mises equivalent mechanical strain amplitudes of pure torsional tests were found in between uniaxial in-phase and out-of-phase tests for the same lifetimes. The non-proportional multiaxial out-of-phase test showed a lower lifetime at the same equivalent mechanical strain amplitude compared to the other types of tests. The microstructure has been characterized applying electron microscopy and microstructural parameters such as fraction of twinned grains, grain size, lamellar distance and dislocation density have been quantified. (C) 2010 Elsevier B.V. All rights reserved.