Effect of microstructure and relaxation behavior on the high temperature low cycle fatigue of near-α-Ti-1100

The influence of lamellar or bi-modal microstructures on high temperature LCF behavior in Ti-1100 was investigated at 600°C. Under various creep-fatigue conditions, as the hold-time increases, the fatigue lives of specimens of both lamellar and bi-modal structures reduce compared with those of continuous cycling of the same specimens. It is understood that longer hold-time results in severe creep damage accumulation due to stress relaxation, leading to reduced fatigue life. Specimens with a bi-modal structure show about double the values of relaxed stress normalized with tensile peak stress of specimens with lamellar structure in the same test conditions, resulting in a higher reduction rate of fatigue life. In addition, as hold-time extends, the difference in total hysteresis loop energy between lamellar and bi-modal structures becomes smaller. Therefore, it can be said that creep damage resulting from stress relaxation during hold-time is more detrimental in bi-modal than in lamellar structures.