Influence of temperature on the low cycle fatigue behaviour of a gamma-titanium-aluminide alloy

In this study, the influence of temperature on the low cycle fatigue behaviour of a cast alloy Ti- 48Al- 2Cr- 2Nb (atomic %) with a lamellar structure is examined. Two temperatures are considered: room temperature and 750°C, which is close to the brittle-to-ductile transition. Fatigue tests are conducted at different total-strain-amplitude values ranging from ±0.2% to 0.8% in air. The strain ratio (R_{ε{closed, reversed}} = ε{closed, reversed}_min/ε{closed, reversed}_max) values of -1 and 0 are used. All tests are carried out at a strain rate of 10³ s¹. For a same total-strain-amplitude, fatigue lives are nearly similar at room temperature and at 750°C. However the cyclic stress-strain behaviour at elevated temperature is different from that observed at room temperature: indeed a strain hardening is observed at room temperature during the whole life while at 750°C a stabilization of the stress amplitude is rapidly reached. A Bauschinger effect is detected at room temperature as well as at elevated temperature.