Isothermal high-temperature fatigue behaviour of a near-γ titanium aluminide alloy

Abstract

AbstractThe high-temperature fatigue behaviour of smooth cylindrical specimens of a near-γ-TiAl alloy with duplex microstructure was studied performing total-strain-controlled low-cycle-fatigue tests in the temperature range 500 – 750 °C. The tests were run in air and high vacuum. Mean stress, environmental degradation (oxygen- and hydrogen-induced embrittlement) and plastic strain range were identified to be the most significant parameters affecting damage evolution. The cyclic stress– strain response was found to depend strongly and characteristically on temperature. Below the brittle-to-ductile-transition temperature (TBD) of about 650 °C, cyclic deformation leads to a pronounced initial hardening manifesting itself in an increase of stress amplitude and a decrease of plastic strain range. Conversely, cyclic deformation curves from tests performed aboveTBDshow a marked state of saturation which is established already after few cycles. With increasing temperature, fatigue life decreases in vacuum. However, testing in air not only decreases fatigue life tremendously as compared to vacuum, but also leads to an inverse temperature effect, i. e., the number of cycles to failure increases with temperature.