Thermomechanical fatigue behaviour of a third generation γ-TiAl intermetallic alloy

Thermomechanical fatigue (TMF) tests with loading conditions involving a combined thermal and mechanical strain cycle were carried out on a third generation γ-TiAl alloy with fine duplex microstructure. The experiments were conducted at a total strain amplitude of 0.6% in out-of-phase (OP) and in-phase (IP) modes. The temperature range was kept constant at 250 °C and the maximum temperatures applied were 700, 750 and 800 °C. The TMF results revealed that thermomechanical loading conditions must be considered as very crucial for the design of components made of γ-TiAl alloys. In particular, out-of-phase loading conditions reduce fatigue life tremendously as compared to the corresponding isothermal conditions. The very short out-of-phase loading life can be attributed to an accelerated oxidation-induced crack initiation during tension in the low-temperature part of the TMF cycle and is a consequence of the formation of an embrittled zone at the surface during the high-temperature part of the loading cycle.