The cyclic deformation and fatigue behavior of the γ-TiAl alloy TNB-V5 is evaluated under thermomechanical load for three different microstructures. For this purpose, strain-controlled thermomechanical fatigue (TMF) tests were carried out with different temperature-strain cycles, different temperature ranges from 400 °C to 800 °C (673 K to 1073 K), and with two different strain ranges to set a fatigue-life relation. Cyclic deformation curves, stress-strain hysteresis loops, and fatigue lives of the tests are presented. The microstructures near-gamma (NG) and duplex (DP) show comparable fatigue lives under all test parameters. The microstructure fully-lamellar (FL) offers longer fatigue lives at the same loading conditions. For a general life prediction, the damage parameter of Smith, Watson, and Topper, PSWTvs fatigue life, is well suitable, if the testing and the application temperature ranges, respectively, include temperatures above the ductile-brittle transition (approximately 750 °C). In the completely brittle material behavior regime the quality of the lifetime prediction is unacceptable. The damage parameter PHL by Haibach and Lehrke shows a comparable correlation to the fatigue life as PSWT. The results are discussed with microstructural investigations.
