Internal crack initiation in high cycle fatigued Ti–15V–3Cr–3Al–3Sn alloys

In the present study, an internal fatigue crack initiation (IFCI) phenomenon in metastable beta Ti–15V–3Cr–3Al–3Sn (Ti–15–3) alloys with various heat treatment conditions was examined. As-solutionized Ti–15–3 alloy was aged in the temperature range between 350 and 500 °C for various duration of time, and each specimen was fatigued at an R ratio of 0.1 and a frequency of 80 Hz. It was found that an IFCI occurred in single phase and metastable beta Ti–15–3 alloys for a wide variety of heat treatment and loading conditions. The operating mechanism for the IFCI in beta Ti–15–3 alloys appeared to be varied depending on the microstructure as a result of different aging practices. The IFCI mechanisms for beta Ti–15–3 alloys were discussed based on the detailed SEM fractographic examinations and EDS analyses.