EFFECTS OF TEMPERATURE AND ENVIRONMENT INTERACTIONS ON FATIGUE CRACK PROPAGATION IN A Ti ALLOY

Titanium alloys are well known as candidates for aeronautical applications in turbine engines because they remain efficient at moderately elevated temperatures. The permanent need to increase the operating temperature requires intensive testing on the fatigue crack propagation behavior of new generation alloys. These alloys are still at an early stage of development and are intended to push the maximum application temperature up to 500 C. As they will be exposed in turbine engines to long term elevated temperatures, oxidation effects must be also taken into account. The upper-use temperature for the usual titanium alloys is about 300 C. Increasing the operating temperature of the material leads to increased environmental influence. Cycling in air can result in significant rapid degradation of the material due to embrittlement at the crack tip as a result of reaction with active species. The present paper deals with a study on fatigue crack propagation (FCP) in a Ti alloy tested in ambient air at temperatures ranging from 300 C to 500 C.