Microstructure degradation in high temperature fatigue of TiAl alloy

Low cycle fatigue properties of lamellar TiAl with 8 at.% Nb were studied at four temperatures: room temperature, 700, 750 and 800 degrees C. Up to 750 degrees C, stable cyclic behaviour is observed while cyclic softening is characteristic for 800 degrees C. The strength of the alloy is still high even at 800 degrees C. The TEM observation did not reveal any substantial changes in the microstructure due to the cycling at RT. At 750 degrees C, the lamellar structure was in some places destroyed by cyclic plastic straining and pure gamma-phase islands with high density of dislocation debris were formed. At 800 degrees C, the domains without lamellar structure cover about 10% of volume and are almost dislocation free. The destruction of lamellar microstructure and possible annealing of dislocation debris is the reason for marked cyclic softening at 800 degrees C. (C) 2013 Elsevier Ltd. All rights reserved.