High temperature fatigue-creep interactive behavior and life prediction of a TiAl alloy

Abstract

The strain controlled low cycle fatigue (LCF) and creep-fatigue interaction (CFI) tests of a TiAl alloy were conducted at 750 °C in air. The strain ratio, strain amplitude and strain rate were –1, 0.4% and 1 × 10–3 s–1 respectively. The high temperature LCF and CFI stress-strain stable hysteresis loop, cyclic hardening/softening, mean stress relaxation and life were studied and compared in details. Morrow modified method and unified life model developed in the present study were employed to predict the fatigue life for LCF and CFI life of TiAl alloy. Finally, the failure mechanisms between LCF and CFI specimens were compared, and some interesting conclusions were obtained. The results show that: (1) there are obvious differences on stress-strain stable hysteresis loop, cyclic hardening/softening, mean stress relaxation and life between LCF and CFI tests; (2) Morrow modified method is not able to predict the fatigue life for LCF and CFI life for TiAl alloy, however, the predicted fatigue life by the unified life model is located in the scatter band of ± 1.5; (3) the fatigue cracks are initiated from the surface for all of LCF and CFI specimens, and LCF specimens show more transgranular appearance while CFI specimens show obvious mixed appearance of both transgranular and intergranular.

Keywords

• tial alloy
• high temperature
• low cycle fatigue
• fatigue-creep interaction
• life predication