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Multi-axial thermo-mechanical fatigue of a near-gamma TiAl-alloy
A material family to replace the current superalloys in aeronautical gas turbine engines is considered to be that of gamma Titanium Aluminide (gamma-TiAl) alloys. Structural components in aeronautical gas turbine engines typically experience large variations in temperatures and multiaxial states of stress under non-isothermal conditions. The uniaxial, torsional and bi-axial thermo-mechanical fatigue (TMF) behaviour of this gamma-TiAl alloy have been examined at 400 - 800 degrees C with strain amplitudes from 0.15% to 0.7%. The tests were conducted at both in-phase (IP) and out-of-phase (OP). The effects of TMF on the microstructure were also investigated. For the same equivalent mechanical strain amplitude uniaxial IP tests showed significantly longer lifetimes than pure torsional TMF tests. The non-proportional multiaxial OP test showed the lowest lifetimes at the same equivalent mechanical strain amplitude compared to the other types of tests.