2001 Volume 42 Issue 7 Pages 1380-1384
In order to investigate the low cycle fatigue behavior of lamellar structured Ti–46.6Al–1.4Mn–2Mo (at%) alloy, total strain range controlled creep-fatigue and continuous fatigue tests (R=−1, strain rate=4×10−3 s−1) were carried out at 800°C. A drastic reduction of fatigue life is observed in creep-fatigue test compared with continuous fatigue test. Microstructural and compositional changes during the creep-fatigue test were investigated using SEM, TEM and AES (auger electron spectroscopy). It was found that this reduction of fatigue life in creep-fatigue test was understood to be due to the additional creep damage occurring during tensile hold time. Recent reports indicate that the lamellar TiAl alloy has a different creep deformation mechanism from general metallic materials. For the lamellar TiAl alloy, it has been reported that creep deformation is controlled not by the self-diffusion assisted dislocation climb but by the dislocation generation due to the α2→γ phase transformation at the lamellar interface. This implies that creep damage induces microstructural phase change during which moving dislocations are generated for the continuous deformation. Therefore, it is very important to investigate the effect of creep deformation on creep-fatigue damage in terms of microstructural change. In the present study, microstructural analysis using SEM, TEM and AES (auger electron spectroscopy) for compositional analysis were conducted. It is found that, under creep-fatigue test, the creep damage causes α2→γ phase transformation at the grain boundary, from which intergranular cracks are initiated to control the creep-fatigue behavior.